Earlier Gen III LS heads, such as those found on LS1, LS6, and various Q Series truck engines, feature tall intake ports referred to as “cathedral” ports. The cathedral-roof shape at the top accommodates the fuel-injector path. The LS2 engine also features cathedral-port heads but is technically considered a Gen IV engine due to the change in cam sensor location. We’ll limit our discussion to Gen IV heads with rectangular intake ports.

In the Gen IV versions of this later generation of LS engines, we’re dealing with two separate cylinder head castings. The LS3, LS9, and L92 all use essentially the same cylinder head foundation, featuring a four-digit identification number, which is at the top of the head just outside the valve cover rail. The casting number for the LS3 head is 0821. The LS9 head features no such casting number; rather, the designation “LS9” is lightly engraved on the lower left of the exhaust side of the head. The LS7 cylinder head is unique, with identification number 8452.

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Gen IV “rectangular”-port cylinder heads include the LS7, LS3, L92, and LS9 variants. Basic differences include intake port dimensions, rocker arm mounting pedestals, and combustion chamber volumes.

All Gen III heads feature tall and narrow cathedral intake ports. This includes LS1, LS6, and LQ truck variants. The LS2 also features cathedral-port heads, although it’s considered a Gen IV engine primarily because the cam timing sensor was moved from the rear of the block to the front timing cover. The cathedral-port design is generally noted for better low-end torque, while the Gen IV rectangular ports are generally known for superior midrange and top-end performance. Cathedral ports measure about 1 inch in width and about 3.125 inches in overall height.

The LS3, LS9, and L92 heads are “as-cast” heads, with intake and exhaust ports and combustion chambers shaped during the precision casting process. The LS7 cylinder head features intake and exhaust ports and combustion chambers with a more refined dimensional and surface finish that is CNC-machined.

Intake port dimensions also vary between the LS3, LS9, and L92 and the LS7 head versions. The intake ports on the head used for the LS3, LS9, and L92 are 1.250 inches wide x 2.550 inches tall, while the intake ports on the LS7 head are 1.350 inches wide x 2.40 inches tall.

The LS7 cylinder head was offered in 2007–2009 Corvette Z06 models. Identifying an LS7 head versus the LS3, LS9, and L92 heads is fairly easy. The LS3, LS9, and L92 heads feature flat rocker pedestals (to accept separate rocker arm rails), and the ports and chambers feature a cast finish. The LS7 head features individual rocker arm radiused stands and all ports and chambers display a machined surface.

From left to right: LS7, LS3, and LS9 cylinder heads. Notice the taller intake ports on the LS3 and LS9 heads.

Shown here is a cutaway view of an L92 head. The intake port runner design differs slightly among the various head versions, but all are very similar in shape.

The LS3 cylinder head has become very popular, in part because of the improved flow of the Gen IV rectangular-port design and its relatively attractive street price. General Motors made a lot of LS3 engines along with its truck counterpart, the L92, and as a result these heads are available in great numbers in salvage yards. Even brand-new head prices have become very reasonable; hence their popularity.

Shown left to right: LS7, LS3, and LS9 heads. Combustion chamber volumes differ among the three variants. The LS7, L92, and LS9 feature 70-cc chambers, while the LS3 has 68.4-cc chambers.

Note that while stock cylinder heads feature a four-boltper-cylinder-head bolt layout, GM LSX versions are offered with a six-bolt-per-cylinder layout. Aftermarket heads are also available in four- or six-bolt versions.

LS7

LS7 cylinder heads feature a larger combustion chamber and wider valve layout. Because of this, LS7 heads cannot be installed onto blocks that feature a cylinder bore size of under 4.100 inches, as valves may contact the top edges of the cylinder bores. LS7 heads may only be installed onto blocks that feature a 4.100-inch or larger cylinder bore diameter. Unlikeother factory LS heads, LS7 factory heads are fully CNC-machined at the combustion chambers and ports. Beneficial porting work may involve only port matching the intake ports and/or the intake manifold ports to remove any potential flow obstructions. Due to the LS7 unique intake manifold deck, only intake manifolds designed for the LS7 heads may be utilized due to port match and manifold bolt pattern.

LS7 heads are casting number 8452 and feature slightly raised ports, altered valve angle, and larger titanium intake valves. Exhaust valves are sodium filled and have been known to cause failures. A popular remedy is a change to stainless-steel exhaust valves. Approximate flow bench results at .600-inch lift are about 370-cfm intake and about 240-cfm exhaust.

LS7 intake port deck view. Note the shorter intake port height compared to LS3, LS9, and L92.

The LS7 heads feature fully CNC-machined combustion chambers with 70 cc of volume.

LS3

The LS3 factory head features lightweight hollow steel intake and solid-stem exhaust valves. In stock form, flow bench results have shown flow rates of 296 cfm intake and 208 cfm exhaust, at full valve lift of about .600-plus. This head is intended for blocks that feature a minimum cylinder bore diameter of 4.00 inches.

The LS3 cylinder head has 260-cc intake runners and 92-cc exhaust ports. In addition, it has a combustion chamber volume of about 68.4 cc. These heads fit any LS engine with cylinder bores of 4.000 inches or larger. It also features 2.165-inch hollow-stem intake valves and 1.59-inch solid-stem exhaust valves.

Shown here is an LS3 combustion chamber with 68.4 cc of volume. All factory production LS heads feature an as-cast combustion chamber except for the LS7, which has CNC-machined chambers.

L92

L92 heads are essentially the same casting as the LS3 heads. The difference is the weight of the intake valves: L92 heads feature solid valves and the LS3 has lighter, hollow-stem valves. L92 and LS3 heads flow pretty well in stock form, but they can benefit from porting by opening up the throats a bit and reducing the big rocker bolt bosses in the runners and massaging the exhaust ports. This is best done on CNC for more precise and repeatable results. CNC porting also requires much less time as opposed to hand porting. Performing a good valve job is more critical, making sure that the seats are concentric and that the valves are sunk into the seat at the same depth.

The L92 combustion chamber features 70 cc of volume.

LS9

The factory LS9 cylinder head was designed for higher dynamic compression to suit a supercharger application. This head features a stronger, more-dense alloy along with beefier webbing reinforcements, again to better handle forced induction pressures. Like the LS7 head, the LS9 features a lightweight titanium intake and hollow sodium-filled exhaust valves. To promote air/fuel mixture efficiency, a “swirl wing” is designed into the intake valve boss at the base of each intake runner. The valve guide boss casting features a pronounced vertical riser, or “wing,” that promotes a swirl effect before the air/fuel charge reaches the valve. In stock form, full-lift flow has been documented at 270 cfm at the intake and 201 cfm at the exhaust ports. CNC port machining that removes the swirl wing has been reported to increase flow to 322 cfm intake and 218 cfm exhaust.

The LS9 CNC-ported cylinder heads have enhanced webbing and a stronger deck for greater rigidity and minimal distortion. The A356T6 alloy also withstands higher-performance service, and in stock trim it is supercharged.

LS9 cylinder head castings are factory etched with an “LS9” designation on the lower left of the exhaust side, under the spark plug port.

The LS3, LS9, and L92 all use essentially the same cylinder head foundation, featuring the four-digit identification number (top of head just outside the valve cover rail) 5364. The LS7 cylinder head is unique, with identification number 8452.

The LS9 and L92 heads feature flat rocker pedestals (to accept separate rocker arm rails). The ports and chambers feature a cast finish. TheLS7 head features individual rocker arm radiused stands and all ports and chambers display a machined surface.

All factory LS heads, including Gen III and Gen IV, are equipped with tapered, or “beehive,” valve springs instead of traditional parallel-wound springs. The beehive spring design, which features an oval wire instead of a round wire, features progressively smaller coils from bottom to top. This was intended to reduce retainer mass and diminish valve spring harmonics/frequencies. However, opinions among performance engine builders vary, opting to choose either beehiveor parallel-wound-style springs. Installed height on LS7 heads is 1.960 inches with 310 pounds at 1.370 inches open pressure. LS3 and LS9 springs feature an installed height of 1.800 inches and 1.250 inches at 295 pounds.

In addition, the LS3, LS9, and L92 heads are originally equipped with the tapered “beehive” valve springs, while the LS7 head features “straight” valve springs without the beehive taper.

An LS9 combustion chamber with 70 cc of combustion chamber volume. The heads come with production lightweight titanium intake valves and sodium-filled exhaust valves.

LS9 cylinder head, deck view. The heads are rotocast from strong A356T6 aluminum alloy, so the molten alloy is equally distributed in the mold for greater density and strength.

Unlike the LS1, LS6, and LS2 heads that feature the tall, skinny cathedral intake ports, the LS3, LS9, L92, and LS7 heads feature a conventional rectangular-shaped intake port. Intake port dimensions also vary between the two head versions. The intake ports on the head used for the LS3, LS9, and L92 are 1.250 inches wide x 2.550 inches tall, while the intake ports on the LS7 head are 1.35 inches wide x 2.40 inches tall.

Cylinder Head Interchangeability

When mixing and matching heads and blocks, the rule of thumb is that you cannot use a cylinder head that features a valve layout that is too large for the bore diameter in the block. For instance, you cannot run an LS7, LS3, or LS9 head on a Gen III block because the valves will contact the edges of the bores. The LS7 head requires the use of 4.100-inch-or-larger bores; theLS3 and LS9 heads require 4.000-inch bores or larger. An exception is the LS2 block, which will accept LS3 or LS9 heads.

While all production-based LS heads and blocks feature a four-bolt design, dedicated performance blocks and heads feature a six-bolt design, where an additional head bolt is added at the inboard and outboard locations, inline with the bore centerline. The added two bolts per cylinder provide extra strength for high cylinder pressures. Blocks that feature this six-bolt design include GM’s LSX block, as well as offerings from various performance aftermarket makers, such as Dart.

You need to pay attention to the block’s bore diameter. Running a cylinder head intended for a larger bore size can result in valves crashing into the block. For instance, you cannot install an LS3, LS9, or LS7 head on an LS1, LS6, or LS2 block (at least not without some creative deck/bore notching to clear the valves).

• LS1 and LS6 blocks will accept only LS1, LS6, and LS2 heads.
• LS2 blocks can use LS1, LS6, or LS2 heads, as well as L92-style heads, which include LS3 and LS9 heads.
• LS3 and LS9 blocks can use LS1, LS6, LS2, LS3, or LS9 heads.
• The LS7 blocks can accept any LS head.

All production LS blocks except the LS3 and LS9 feature a 4-bolt-per-cylinder head bolt layout, for a total of 10 head bolts per head. All these heads use 11-mm x 2.0 thread except the LS9, which features 12-mm x 1.75 thread. However, the GM LSX race block, LS3, and LS9, along with a host of aftermarket race blocks, feature a 6-bolt design, with 18 bolts total per head. Two additional bolts per cylinder, one inboard and one outboard of the bore centerline, are added. This provides added head securing and rigidity for high-cylinder-pressure applications.

Regarding head-to-block swaps, the four-bolt heads or the six-bolt heads can be installed on either four-bolt or six-bolt blocks. Installing a four-bolt head to a six-bolt block simply won’t provide the added cylinder head clamping available with the six-bolt head. Also, while a six-bolt head can be installed to a production four-bolt block, you simply won’t be taking advantage of the added bolt locations offered by six-bolt heads. Appearance-wise, the outboard four-bolt bosses simply hang over the block deck but won’t cause an issue. If a six-bolt head is installed on a four-bolt block and you don’t like the looks of the extra bosses on the exhaust side of the heads, these bosses can be milled off, but this is not necessary.

This Tech Tip is From the Full Book, LS GEN IV ENGINES 2005 – PRESENT: HOW TO BUILD MAX PERFORMANCE .

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

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Shown here is an example of a six-bolt head, from Trick Flow. Aftermarket head makers offer LS heads in both four-bolt and six-bolt designs. Six-bolt block and head combinations require a special head bolt or head stud kit and head gasket designed for the six-bolt platform.

A six-bolt head can be mounted to a factory four-bolt block, even though you would not be taking full advantage of the head’s six-bolt design. The outer bolt bosses would simply hang out past the block deck. If this is the case, the extra outboard bosses may be milled off if so desired. This would occur only if you happened to get a good deal on a pair of six-bolt heads that you wished to use on your factory block.

Water Temp Holes

All LS heads feature a 12-mm x 1.5 female-threaded hole on the left of the exhaust side, intended for a water temperature sender. The sender is traditionally mounted to the left-hand head, but don’t forget to plug the hole on the right-hand head. If you’re dealing with a new or used head, this plug will already be in place with any luck. If the plug is missing, you can handle this in one of two ways: purchase a GM plug PN 11610259 for about $5, or simply use a 12-mm x 1.5 bolt with a shank length of about 20 mm along with an aluminum or copper crush washer. If the heads have been reconditioned, this plug on the right head might have been accidentally lost or ignored. It’s easy to forget, so make sure to plug this unused water hole; otherwise you’ll have a coolant-squirting mess when you start the engine.

Each head features a 12-mm x 1.5 threaded hole on the left area of the exhaust side. These holes are open to the cooling. The water temperature sender installs to the left-side head.

An example of a water hole plug on the right-side cylinder head, using a common 12-mm x 1.5 bolt and crush washer.

Rocker Arm Pedestal Rails

Two different rocker arm pedestal rail versions are used. One rail is designed for use on the LS1, LS6, and LS2. The other is designed for the L92, LS3, L99, and LS9.

The rail for the LS1, LS6, and LS2 features the pedestals centered (height-wise) on the rail. Each edge of the rail’s length is straight. The rail for the L92, LS3, L99, and LS9 locates the pedestals a bit offset, with one side of each pedestal extended out (one edge of the rail features individual pedestal bulges, or radiuses, that protrude out from the edge).

Gen IV rocker arms for L92, LS3, and LS9 applications feature an offset intake rocker and a straight exhaust rocker, both with 1.7:1 ratio.

Cast-in rocker pedestals are integral to the LS7 heads. The radiused pockets allow rockers to be directly bolted to the heads without the need for a separate rocker mounting rail.

The rail for the LS1, LS6, and LS2 features each cylinder’s pair of pedestals located 1.901 inches on center from each other. The rail for the L92, LS3, L99, and LS9 features the pedestal centers located 2.227 inches apart (center of hole to center of hole). The part numbers on the rails are 12552203 for the LS1, LS6, and LS2 rails and 12600936 for the L92, LS3, L99, and LS9 rails. The LS7 cylinder heads feature individual radiused rocker stands as an integral aspect of the casting and do not require the use of a separate rocker arm mounting rail. Rockers bolt directly to the LS7 heads without the need for a separate rail.

As an example of a pair of performance aftermarket rockers for LS Gen IV applications that require offset intake rockers, this underside view shows the slight offset of the intake rocker (left) at both the pushrod cup and roller valve ends. The offset intake rockers are necessary because of the larger valve diameters used in Gen IV applications.

A comparison of the rocker pedestal design on the LS7 head (left) and LS2/LS3/L99/LS9 head versions. Note that the LS7 rocker pedestals are part of the casting, allowing the rocker arms to bolt onto the head with no need for a mounting rail. The other style features flat pedestals, onto which a separate rocker arm mounting rail is installed. The rail is sandwiched between the head and rockers.

Factory original Gen III and Gen IV heads feature separate rocker mounting rails that allow mounting OEM rockers except for LS7 heads, which do not require a mounting rail. Note that Gen III and Gen IV rails seen here at the bottom are different; the Gen IV rails feature a different rocker arm mount spacing.

This view shows the underside of the rocker rails. Gen III rails have about the same amount of material above and below the holes, while Gen IV rails feature protrusions with the bolt holes slightly offset from the center length.

Aftermarket Performance Heads

Stock LS cylinder heads provide superior breathing compared to Gen I small-block Chevy heads. Since the introduction of the LS engine, cylinder head architecture has improved, and the original cathedral intake port design has evolved to rectangular-port designs, with the LS3/L92 heads currently leading the pack in terms of performance attributes. Thanks to performance aftermarket manufacturers, even furtherhorsepower gains are to be had. In some cases, gains of roughly 100 hp over stock have been realized because of changes in runner design, valve angle, port height variations, precision CNC-machined chambers and ports, capabilities to accommodate larger/taller aftermarket rockers and springs, increased deck thickness for added rigidity, and more. When you want to extend the power, torque, and RPM envelope, upgrading to aftermarket heads is definitely a move to consider.

Several companies offer aftermarket performance LS heads, including examples from Trick Flow, Dart, Mast Motorsports, Air Flow Research (AFR), Edelbrock, Racing Head Service (RHS), Bill Mitchell Products (BMP), and World Products. A wide array of configurations is available, including those with cathedral-port intakes (Gen III and LS2) as well as those with rectangular-port intakes (LS3, LS7, and L92). Heads are available in bare form and fully assembled, and as-cast or CNC-machined. Choices also abound in terms of intake port volume, combustion chamber volume, and both four-bolt-per-cylinder and six-bolt-per-cylinder formats.

Selecting a Cylinder Head

With all the variations in LS cylinder head platforms, choosing the head that’s right for your build can seem daunting at first. The first two considerations involve the type of intake manifold port and the piston bore size of your block. There are three types of factory intake ports: cathedral, square port, and raised square port. The cathedral-port design was featured on Gen III engines LS1, LS6, and LS2, as well as Vortec 4.8L, 5.3L, LQ4, and LQ9 iron blocks. The squareport, which is actually a rectangular port, is featured on factory L92, LS3, L99, L76, LS9, and LY6 engines. The raised square port was found on LS7 and GM LSX engines.

All three port designs flow well and produce good power. The cathedral port offers decent torque and is slightly more streetable, with the square-port designs offering higher peak horsepower at higher RPM, more suited for competition use. For the street, cathedral or square is acceptable for moderate power builds. For optimum power at higher engine speed, the square port is preferred. Naturally, the intake manifold must feature the same type of port to match the head.

The piston bore size is a critical factor. The 3.89-inch bore found on LS1 and LS6 engines will accept only cylinder heads that were intended for LS1, LS6, or LS2 applications. Using heads designed for a larger bore size runs the very real risk of valves contacting the edges of the cylinder bore. LS2 and LQ9 blocks feature a 4.000-inch bore and accept heads designed for LS1, LS6, LQ9, L92, LS3, and LS9 engines.

Other considerations involved in selecting the best cylinder head for your application include the weight of the vehicle, camshaft, intake manifold, exhaust system, transmission, gear ratio, drive tire diameter, and intended use. Aftermarket cylinder head manufacturers offer all three port designs, but with a range of intake and exhaust port volumes beyond what the factory heads provide. It’s best to discuss your build with the head maker for help in choosing a head. For instance, steeper gearing and/or high camshaft lift will likely require larger port volumes.

Trick Flow’s GenX 255 head is designed for six-bolt-per-cylinder block applications. Note the “extra” outboard bolt bosses.

The GenX 255 head features rectangular intake ports, CNC-finished. Airflow tests with a bore size of 4.065 inches are impressive. At .400-inch lift, intake flow was rated at 294 cfm and exhaust flow at 215 cfm. At .600-inch lift, intake flow was 363 cfm, with exhaust flow at 252 cfm. At a whopping .700-inch lift, flow rose to 383 and 258 cfm respectively.

Trick Flow

Trick Flow’s line of LS heads offers a dizzying array of cylinder head configurations in LS1, LS6, and LS2 cathedral-port and Gen IV rectangular-port designs. Offerings include as-cast and CNC-machined versions, in both bare and fully assembled configurations in a wide range of intake port volumes.

One example is its GenX 255 head for LS3 applications, PN TFS-3261T003-C01.

Dart

Dart offers both LS1-based (cathedral-port intakes) and Gen IV LS3–compatible versions, as well as a dedicated racing head. Its LS1-, LS6-, and LS2-based designs include the Pro 1 15-degree head in three different versions: 205-, 225-, and 250-ccintake runners. The Gen IV Pro 1 LS3–style head offers 280-cc intake runners and a six-bolt-per-cylinder fastener layout. Targeted at serious drag race applications, the Gen IV LS3–compatible Race Series rectangular-port head features 10-degree valve angles and a whopping 280-cc intake runner volume. The competition-only heads are unique, featuring 10-degree canted valves, with intake and exhaust valve locations reversed, and huge oval-port 368-cc intake runners. Dart’s line is designed for bore sizes of 4.125 inches or larger and for six-bolt-per-cylinder blocks.

Dart begins its offerings with the Pro 1 205-cc or 225-cc LS1, LS6, and LS2 head, equipped with beehive springs and cathedral intake ports. (Photo Courtesy Dart)

Dart’s Gen IV LS3–style head is intended for 4.125-inch bores or larger and accommodates six-bolt-per-cylinder blocks. Valve angle is 10 degrees, with canted valves. Intake and exhaust valve locations are reversed. It features 368-cc intake runners with oval ports. This is a serious race-only drag head. (Photo Courtesy Dart)

The Pro 1 LS3 head features a six-bolt-per-cylinder format, with 280-cc intake runners and rectangular intake ports. (Photo Courtesy Dart)

Air Flow Research (AFR)

AFR’s Mongoose line includes both cathedral-port-design LS1 and rectangular-port-design LS3. All heads are 100-percent port and chamber CNC-machined and include titanium retainers. The Gen III LS1 line offers intake runner volumes of 210, 215, 230, and 245 cc. All feature 15-degree valves.

AFR’s LSX Mongoose line of cylinder heads offers a selection of cathedral-port LS1 and LS2 heads, including intake runner volumes of 210, 215, 230, and 245 cc. Pictured here is the 215-cc version. (Photo Courtesy AFR)

The LS3-style head features 12-degree valves and 260-cc intake runner volume. It has 69-cc combustion chambers with 2.165-inch intake valves and 1.600-inch exhaust valves, dual 1.270-inch valve springs rated at 155 pounds at the seat, 8-mm bronze valve guides, and ductile iron valve seats.

MAST Motorsports

Mast’s Black Label line of LS heads offers both cathedral-port and rectangular-port heads. All Black Label heads feature a deck thickness of .750 inch. Mast offers a wide range of configurations.

In the LS1 and LS2 cathedral-port family, the following are available:

• LS1/LS2 225 cc for 3.890+ bore
• LS1/LS2 245 cc for 4.000+ bore
• LS1/LS2 275 cc for 4.125+ bore
• LS1/LS2 295 cc for 4.125+ bore

In the LS3 style range, the following are available:

• LS3 240 cc for 3.890+ bore
• LS3 280 cc for 4.125+ bore
• LS3 LSA 255 cc for 4.000+ bore

In the LS7 style, offerings include the following:

• LS7 265 cc for 4.000+ bore
•  LS7 285 cc for 4.125+ bore
• LS7 305 cc for 4.125+ bore

In addition to the cathedral- and rectangular-port versions, Mast also offers an “all-out” race-only cylinder head called the Str8jacket Head, in a medium format for bore sizes of 4.000 inches or larger and the large for bores of 4.125 and larger. Both versions feature 47-cc combustion chambers and inline 11-degree valve layout. The medium bore head is equipped with 2.250-inch intake valves and 1.570-inch exhaust valves. The large bore head uses 2.300-inch intake valves and 1.600-inch exhaust valves. Valve spring options are based on specific lift requirements. Valves are offered in either titanium/ titanium or titanium/solid stainlesssteel packages.

Edelbrock

Edelbrock offers cathedral port heads for LS1, LS6, and LS2 Gen III and IV applications and a Gen IV LS3–style head. The LS3 head is offered to fit stock LS blocks with a four-bolt-per-cylinder layout or LSX-style blocks with six bolts per cylinder. The LS1, LS6, and LS2 head is offered with an intake runner volume of 215 cc, while the LS3 head features 230 cc.

Racing Head Service (RHS)

RHS’s Pro Elite line of LS heads includes a hefty array of LS7-style versions, with one even applicable to small-bore LS1/LS2 blocks. Rather than featuring the traditional cathedral intake ports found on other LS1/ LS2 heads, the small-bore LS7 head features LS7-style rectangular intake ports, providing a power upgrade that allows earlier engines to take advantage of the PS7 head design. This small-bore head features 260-cc intake runners that are raised .220 inch for a straighter shot to the cylinder.

In addition to the small-bore version, seven versions of the LS7 larger-bore heads are available, all with 29-cc intake runner volume. Differences are chamber volumes, types of valves and springs, and applications for hydraulic or solid lifters.

All heads in the Pro Elite series feature a six-bolt pattern, which allows installation in either four-bolt or six-bolt blocks. Heads are available bare or fully assembled.

Bill Mitchell Products (BMP)

Bill Mitchell Products (BMP) offers a killer LS7X head featuring hardened seats; bronze valve guides; spring seats machined for 1.560-inch springs (can be machined for 1.625-inch); Manley stainless-steel valves; 2.250-inch intake valves and 1.625-inch exhaust valves; CNC porting; 12-degree valve angle; flat-machined rocker pedestals that accept T&D rocker system 2351; 285-cc or 296-cc rectangular-port intake runners; 106-cc or 112-cc exhaust runners; 64-cc combustion chambers as cast, or 74-cc CNC; and a valve cover rail raised .300 inch for added rocker clearance. The head features a six-bolt head bolt pattern, allowing installation to four- or six-bolt blocks.

BMP’s LS7X head is offered with either 285-cc or 296-cc intake runner volume, and with either as-cast 64-cc combustion chambers or CNC’d 74-cc chambers. The rocker rail pedestals feature radiused pockets to accept a T&D rocker system. (Photo Courtesy BMP)

Written by Mike Mavrigian and republished with permission of CarTech Inc

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 Camshaft Terminology

A brief explanation of camshaft terminology and specifications follows here, citing information provided by Lunati as the examples.

Nose

The camshaft lobe nose is the highest point that provides maximum valve lift, between the opening and closing ramps of the lobe.

High-performance roller lifters are available individually to use with OEM plastic lifter guides or as tie-bar-connected pairs that eliminate the need for the plastic lifter guides. The only downside of using tie-bar roller lifters is that during a camshaft change, the lifters must be removed in order to reach the cam. The plastic lifter guides allow you to pop the lifters up and away from the cam lobes without the need to remove the lifters. With the rocker arms and pushrods removed, by rotating the crankshaft twice, the lifters are pushed up into the “locking” position where they are slightly gripped by the guides, holding the lifters up and out of the way. However, not having that feature is a small price to pay for the advantage of the extremely durable tie-bar roller lifters that are available in today’s aftermarket.

Base Circle

The base circle, also referred to as the lobe heel, is the lowest point of the lobe. This is the point at which the valve is in the fully closed position and the point at which valve lash adjustments are made. When measuring for a custom pushrod length, the lifter is at its lowest point, where pushrod length is measured between the lift cup and rocker arm.

Symmetrical Lobes

Lobes that are symmetric are machined with mirror-image/identical opening and closing ramps on each side of the lobe.

Asymmetrical Lobes

Asymmetrical lobes are machined differently at the opening versus closing ramps. Typically, an asymmetric lobe provides a faster/higher-velocity opening ramp and a slower-velocity closing ramp. This allows the valve to close with less impact force.

Lift

Lift refers to how far the valve is raised from its seat when completely open. Note that lobe lift and valve lift differ. Lobe lift refers to the distance from the base circle to the lobe peak. Valve lift considers both lobe lift and rocker arm ratio. Valve lift is easily calculated by simply multiplying the lobe lift by the rocker arm ratio. For example, if the cam features a lobe lift of .377 inch and is coupled with a rocker arm ratio of 1.7:1, the effective valve lift is .641 inch. If a 1.8:1 rocker arm ratio is used with the same cam, the effective valve lift is 0.678 inch.

The intake and exhaust valves need to open to let air/fuel in and exhaust out of the cylinders. Opening the valves quicker and farther usually will increase engine output. Increasing valve lift without increasing duration can yield more power without much change to the nature of the power curve. However, an increase in valve lift almost always is accompanied by an increase in duration because the lobe ramps are limited in their shape, which is directly related to the type of lifters being used, such as flat tappet or roller.

While many cams may feature more lift on the exhaust side than the intake side, this is primarily done to help compensate for less-than-efficient exhaust ports. Today’s high-performance LS heads feature improved flow, so you’ll see cams available with more intake lift to help draw more mixture into the chambers.

Duration

Duration represents the angle in crankshaft degrees that the valve stays off its seat during the lifting cycle of the camshaft lobe. Increasing duration keeps the valve open longer and can increase high-RPM power. This also increases the RPM range where the engine produces power. Increasing duration without a change in the lobe separation angle (LSA) will result in increased valve overlap.

When you view cam specifications, advertised duration and duration at .050 inch will be listed. This is the angle in crankshaft degrees that the lifter is lifted more than a predetermined amount off its seat. Because advertised duration can vary depending on cam makers, based on a predetermined point chosen by the cam maker, an industry standard of listing duration at .050 inch allows direct comparison of duration across all brands. Duration at .050 is a measurement of the movement of the lifter, in crankshaft degrees, from the point where it first lifts .050 inch from the base circle on the opening ramp side of the cam lobe to the point where it ends up being .050 inch from the base circle on the closing ramp’s side of the lobe. This is the industry standard and is a good value to use to compare camshafts from different manufacturers.

Lobe Separation

Lobe separation, referred to as LSA, is the angle in camshaft degrees between the maximum lift points of the intake and exhaust valves. Lobe separation affects valve overlap, which affects the nature of the power curve, idle quality, and idle vacuum. LSA can be measured using a dial indicator and a degree wheel, but it is usually calculated by dividing the sum of the intake centerline and the exhaust centerline by two. In very general terms, a low LSA, let’s say from 106 to 108 degrees, for example, may produce a rougher idle and lower engine vacuum at idle and move the power band to the mid-to-high RPM range. A larger LSA, let’s say in the 112- to 114-degree range, would produce a smoother idle and more engine vacuum at idle and would move the torque curve to the lower RPM range for quicker response and a broader RPM band.

Overlap

Overlap refers to the angle in crankshaft degrees that both the intake and exhaust valves are open. This occurs at the end of the exhaust stroke and the beginning of the intake stroke. Increasing lift or duration and/or decreasing lobe separation increases overlap. At high engine speeds, valve overlap allows the rush of exhaust gasses out of the exhaust valve to help pull the fresh air/fuel mixture into the cylinder through the intake valve. Increased engine speed enhances this effect. Increasing overlap increases top-end power and reduces low-speed power and idle quality. Overlap can be calculated by adding the exhaust closing and the intake opening points. For example, a camshaft with an exhaust closing point at 4 degrees after top dead center (ATDC) and an intake opening point at 8 degrees before top dead center (BTDC) has 12 degrees of overlap. Decreasing the lobe separation by only a few degrees can have a huge effect on the overlap area.

Camshaft lobe separation, referred to as LSA, is the angle in camshaft degrees between the maximum lift points of the intake and exhaust valves. Lobe separation affects valve overlap, which affects the nature of the power curve, idle quality, and idle vacuum. LSA can be measured using a dial indicator and a degree wheel, but it is usually calculated by dividing the sum of the intake centerline and the exhaust centerline by two. (Photo Courtesy Lunati)

The camshaft centerline is the point halfway between the intake and exhaust centerlines. The intake centerline is the highest point of lift on the intake lobe, expressed in crankshaft degrees after top dead center (ATDC). The exhaust centerline is the highest lift point on the exhaust lobe, expressed in crankshaft degrees before top dead center (BTDC). (Photo Courtesy Lunati)

Centerline

The intake centerline is the highest point of lift on the intake lobe, expressed in crankshaft degrees after top dead center (ATDC). The exhaust centerline is the highest lift point on the exhaust lobe, expressed in crankshaft degrees before top dead center (BTDC). The camshaft centerline is the point halfway between the intake and exhaust centerlines.

Cam Advance and Retard

Advancing or retarding the camshaft moves the engine’s torque band around the RPM scale by moving the valve events farther ahead of or behind the movement of the piston. Typically, a racer will experiment with advancing or retarding a camshaft from the “straight up” location. In general terms, advancing a cam will improve low-end power and response, while retarding a cam biases the torque band to favor high-end power.

Advancing or retarding the camshaft moves the engine’s torque band around the RPM scale by moving the valve events farther ahead or behind the movement of the piston. With the use of an adjustable aftermarket cam timing gear set, you’re able to advance the cam to improve low-end power and response, or retard cam timing in favor of high-end power.

Advancing the cam position begins the intake event sooner, opens the intake sooner, builds more low-end torque, decreases piston-to-intake valve clearance, and increases piston-to-exhaust valve clearance. Conversely, retarding the cam position delays the intake event and opens the intake valve later, builds more high-end power, increases piston-to-intake valve clearance, and decreases piston-to-exhaust valve clearance.

Factory Camshafts

Listed here are specifications for stock production camshafts in Gen IV engines. All factory LS engines feature hydraulic roller lifters and roller camshafts.

Active Fuel Management (AFM)

Some LS engines feature active fuel management (AFM) involving either displacement on demand (DOD) or variable valve timing (VVT). DOD essentially shuts off specific cylinders via oil-pressure/ spring-controlled/spring-assist special lifters when engine demand is low. VVT works by adjusting valve timing depending on engine RPM: retarding valve timing at high RPM and advancing timing at low RPM. The goal of either system is, in theory, to gain fuel economy. In reality, for a high-performance build, it’s best to delete these systems to obtain maximum power potential. To delete an active fuel management system and take advantage of a high-performance aftermarket camshaft, active fuel management delete kits are readily available, both for DOD and VVT systems.

DOD System

A DOD system disables half of the cylinders (1-4-6-7) under cruising or low-load conditions by collapsing the lifters in those cylinder locations and by cutting the spark for the same cylinders. When demand increases, the lifters are activated and “normal” lifter performance returns. The system is operated by the engine control unit (ECU) and four solenoids located in the upper valley, attached to the valley plate assembly known as a lifter lower manifold assembly (LLMA). The solenoids provide pressurized oil to the special roller lifters. The system is tuned to a specific factory camshaft, with the lobe profiles between the AFM and non-AFM cylinders different because of different valve lash requirements. Upgrading to a high-performance camshaft requires not only the new camshaft, but also replacing the special AFM lifters and lifter retainers, replacing the valley cover, eliminating the four solenoids, and plugging the oil delivery towers in the valley. In addition, the ECU must be reflashed/recalibrated. Plugging the oil towers is outlined in chapter 2.

DOD lifters feature “assist” springs. When the engine is under light load, the ECU signals a cutoff of oil supply to the select DOD lifters, allowing those lifters to collapse so that the intake and exhaust valves in the DOD locations close, shutting off firing to the four select cylinders. The spring on the DOD lifters maintains just enough pressure to the pushrod to prevent the pushrods from loosening and falling out. The DOD lifters feature a notched anti-rotation design that differs from standard LS lifters, requiring a different DOD-specific plastic roller guide tray.

While DOD or VVT factory cams might feature a single-bolt cam gear and cam, most aftermarket performance cams feature a three-bolt design. Because of this, part of deleting AFM involves obtaining a new 4X cam gear that features a three-bolt design.

DOD roller lifters retain the same .750-inch-diameter roller as standard LS roller lifters.

Using a DOD camshaft along with a DOD delete kit won’t work; it will result in a misfiring engine. A non-DOD camshaft is required.

VVT System

The VVT AFM system operates by the ECU monitoring valve timing through the camshaft position sensor. The ECU sends a signal to a solenoid that’s mounted to the timing cover. The solenoid controls oil flow through a control valve built into the single camshaft bolt, operating a camshaft phaser actuator on the timing cover that rotates to advance or retard the camshaft.

A DOD delete kit, required for installing a non-DOD camshaft, includes a set of standard LS, non-DOD lifters, lifter guides, valley cover, new OEM-style head bolts, head gaskets, PVC hose, and PCV plug. This example is Trick Flow’s PN 30678503. (Photo Courtesy Trick Flow Specialties)

VVT was first employed in select 6.0L and 6.2L LS engines. The front-mounted actuator controls the amount of intake and exhaust valve overlap. The engine’s ECU commands the actuator to advance or retard the camshaft. The VVT camshaft features an internal oil passage that sends oil to the actuator. The actuator uses oil hydraulic pressure to change the camshaft timing. An actuator magnet is mounted to the front face of the timing cover, connected to 12 volts. When the solenoid is energized, the electromagnetic force on the magnet positions the spool valve of the solenoid. During engine operation, the ECU adjusts cam timing within a range of about 7 degrees of advance to about 55 degrees of retard.

An example of a VVT delete kit from Trick Flow Specialties, PN 30678505. A new timing cover (type LS2/LS3) featuring the camshaft phaser actuator is included to replace the VVT cover. (Photo Courtesy Trick Flow Specialties)

The VVT system features a single-bolt camshaft. The cam bolt incorporates an internal spool valve with an internal check ball and filter. Pressurized oil that runs through the cam is sent through the spool valve to control the timing actuator. The valve spool directs oil out of advance/retard oil ports to the actuator.

The VVT system doesn’t like high-performance cams, which limit valve lift and duration. Also, higher valve spring pressures required for a high-performance cam can overwhelm the actuator. Just get rid of the VVT. Deleting a VVT system is slightly less intrusive or complex than performing a DOD delete. Deleting VVT only requires swapping out the cam gear, timing cover, cam position sensor, and cam gear bolts, in addition to the performance camshaft of choice. The ECU will also need to be recalibrated for non-VVT operation. A VVT delete kit will be necessary when removing the active fuel management VVT system from a Gen IV engine.

The nose of the VVT cam bolt/spool valve features a face protrusion that contacts the magnet of the timing cover cam position actuator.

The cam position actuator magnet mounts to the exterior of the timing cover. The power connector is positioned at about seven o’clock when mounted.

The rear of the cam position actuator magnet places the electromagnet facing the VVT cam bolt/spool valve nose.

Typical delete kits include a three-bolt 4X cam timing gear, timing chain damper, LS2/LS3 timing cover, eight timing cover bolts, timing cover gasket, timing cover front seal, cam position sensor, cam sensor harness bracket, cam sensor harness, three ARP camshaft bolts, and water pump gaskets. The cam sensor features a three-pin connector, as opposed to the five-pin VVT connector. To use the new sensor, you need to remove the wires from the three-pin connector and reuse theoriginal five-pin connector, or you can simply swap the cam sensor from the existing VVT cover to the new cover. Some kits also include a new camshaft retainer plate and crankshaft bolt.

A VVT camshaft features an internal oil passage that allows pressurized oil to be delivered to the cam bolt/spool valve. The majority of aftermarket performance camshafts feature a three-bolt design, so a three-bolt cam timing sprocket is needed to accommodate the new performance cam.

Gen IV LS3 and LS7 engine packages offer tremendous power potential due to the larger displacement and superior-flowing cylinder heads, but the weak spot involves the camshaft. Factory cams are designed to provide a compromise between power, torque, idle quality, and fuel mileage. Substantial power gains can be had by simply changing cam profile, by as much as a whopping 70 hp. Keep in mind that factory valve springs are mated to the factory cams. When increasing valve lift and extending the RPM range, higher-rated valve springs must accompany a cam swap.

As far as AFM systems are concerned, whether DOD or VVT, just eliminate this nonsense. Each system involves added components that increase the potential for parts failures, and they limit performance potential. If you’re after optimum performance for the street or track, just delete the AFM and get back to basics that allow you to take advantage of LS power potential. However, if your primary goal is to improve fuel economy instead of maximizing power, just buy a Prius hybrid and blend into the crowd of non-car folks.

Intake and Exhaust Difference

While some cam makers choose to use the same lift at intake and exhaust locations, some prefer to use a bit less lift at the exhaust to promote better exhaust scavenging. Exhaust valves are smaller than intake valves, so we have less exhaust volume than intake volume. Exhaust exits the cylinder head based on piston displacement, cylinder pressure, and header pull-out scavenging. By running less lift at the exhaust valve than at the intake, the exhaust can speed up, creating more vacuum and exiting faster. If exhaust volume is too large, it can reverse, which is detrimental to power.

The use of electronic fuel injection (EFI) in LS engine applications is obviously commonplace, but if you decide to run a carburetor setup, you have two basic choices in terms of duration and lobe separation. If you run a carburetor with a cam that has a shorter duration and tighter lobe separation, the engine will be “snappier,” building peak power more quickly but also losing it more quickly. However, by running a longer duration and wider lobe separation, you broaden the power curve for better midrange and top end.

Camshaft Firing Order

In certain racing applications, a special firing order camshaft (SFO) can be used as a tuning aid, allowing the competition engine builder to further address combustion heat and crankshaft disturbance (harmonic) issues. The goal in changing firing order is to create a smoother-running engine, more-even fuel distribution, and enhanced crankshaft and main bearing durability. In the process, horsepower gains may be achieved as well (no guarantees here, but in most cases a slight power increase does result).

The traditional firing order for Chevy small-block and big-block engines has always been 1-8-4-3-6-5-72, which is determined by the crankshaft rod pin layout. Each cylinder has a “companion” in the firing order. This companion cylinder will reach top dead center (TDC) at the same time as its counterpart, one on the power stroke and one on the exhaust stroke. These cylinders are paired as 1 and 6, 2 and 3, 4 and 7, and 5 and 8; these can be interchanged in the firing order without altering the crankshaft. Some builders report seeing no power improvement, and other builders claim to have achieved power gains by switching cylinders 4 and 7 to create a new firing order of 1-8-7-3-6-5-4-2. This can enhance fuel distribution, especially in open plenum–type intake manifolds, and reportedly can result in an added 5 to 10 hp.

For example, Pro Stock drag engines typically take advantage of a 4/7 swap. Swapping number-7 and number-4 cylinders in the firing order eliminates the fuel distribution and heat problems caused by cylinders number-5 and number-7 firing in succession. With the revised firing order, the two end cylinders do not have to fight for fuel from the manifold plenum. The result, in many cases, is a measurable power increase(typically 8 to 10 hp) and a smoother, cooler-running engine.

Playing with special firing orders isn’t limited to the advanced race engine builder. General Motors adopted a special firing order in its Gen III and IV LS engine series, which feature a 4/7 and 2/3 swap for the same reasons: to smooth out the harmonics in the pursuit of greater engine durability and to potentially generate more power. In the early development of the LS, GM’s analysis showed that main journal number-4 had peak leads that were significantly higher than in main number-2. By changing the firing order to 1-8-7-2-6-5-4-3, the peak loading on main number-4 was reduced and the peak loading on number-2 went up. Overall, the loading among the main journal locations showed improved balance. In turn, the oil film between main bearings and main journals was better balanced at all main locations.

The primary reason to alter cylinder firing order is to achieve a smoother-running engine that delivers a more lineal acceleration ramp with less harmonic effect and crank deflection on the crankshaft and its main bearings. The goal of swapping firing order positions is to reduce crankshaft harmonic effects caused by two adjacent cylinders firing in succession (companion cylinders). By strategically relocating these companions, it’s possible for the engine to idle and run smoother, to reduce isolated hot spots (cylinder-to-adjacent-cylinder walls), and to even out fuel distribution, primarily in applications that feature a single-plane intake manifold, and even more noticeably in tunnel ram intake manifold applications.

With a fuel injection setup, a lean cylinder can be richened (via the engine controller) to eliminate detonation, so firing order changes may not be as beneficial in an injected engine because fuel is delivered on an individual-cylinder basis. However, the LS firing order takes advantage of a 7/4 and 3/2 swap as an additional tuning aid, to produce an even smoother acceleration profile and to benefit crank and bearing life.

Hydraulic or Solid

Hydraulic camshafts are designed to use hydraulic roller lifters. Once valve lash is set, no further lash adjustments should be needed. Hydraulic lifters provide smooth response and the hydraulic valve inside the lifter compensates for harmonics and for thermal expansion and contraction and dampens shock to the cam and valvetrain, making them ideal for street use.

Solid roller cams and lifters are intended for maximum performance and allow the use of more aggressive cam profiles. Solid cam and lifter combinations also better withstand higher valve spring pressures. When valve lash is set to the tight side of around .010 to .012 inch, solids also offer superior throttle response. The limitations, or drawbacks, if you will, involved with solid lifters include a higher price tag; the need for periodic valve lash adjustment due to variations of heat and thermal dynamics; increased noise, especially during cold starts; and poor suitability for extended low-RPM operation. Yes, a solid roller cam can be used in street applications, but routine checking and adjustment of valve lash is mandatory, something that many street enthusiasts may not be willing to perform. In short, for a street application, go with hydraulic. For racing use, go with solids. Aftermarket cam makers offer a wide range of profiles for LS applications in both hydraulic and solid formats.

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Examples of extreme-duty race-level lifters include those offered by Comp, Lunati, Morel, and Gatorman (formerly Crane, available through Howards Cams), and for extreme-duty solid rollers, a brand called BAM.

Cam Gears

All Gen IV camshaft gears feature a 4X reluctor lug pickup design, for front-mounted camshaft position sensor location. On Gen III engines the camshaft position sensor was mounted at the top rear of the block. This is an easy way to identify a Gen III versus a Gen IV engine.

Gen IV cam gears feature a three-bolt hole pattern for cam attachment except the 2007 LS2 and 2008 LS3 and LS9, which feature a single-bolt mount.

The three-bolt 4X cam gear is designed for a front-of-block-mounted camshaft position sensor. Note the timing notch, which aligns at six o’clock in relation to the crank gear at twelve o’clock, with the number-1 piston at TDC with the number-1 valves closed. All LS cam gears feature this timing reference notch.

Aftermarket performance cam makers offer LS cam kits that include either OEM-style LS roller lifters, as shown here, or lifters that are tied together in pairs via a link bar. The LS lifters that copy the factory lifter dimensions and basic design allow the use of the original plastic lifter guides, whereas linked lifters eliminate the need for the plastic guides. Aftermarket cam makers such as Crane, Lunati, Comp, Bullet, and others offer an extremely wide selection of cam profiles for any LS application, from mild street to extreme race applications.

All Gen IV cam gears mount to the camshaft with a three-bolt attachment. The exceptions are the 2007 LS2 and 2008 and later LS3 and LS9 applications that feature a single center-bolt gear-to-cam mounting. However, aftermarket cams and cam gears are available for LS3 and LS9 applications that feature a three-bolt design.

The three-bolt Gen IV cam gear, featuring a 4X lug for Gen IV camshaft position sensor pickup, is available as PN 12586481 (shown at left). Three-bolt 1X cam gears, PN 12576407, were used only in 2005 LS2 Corvette and 2005–2006 LS2 GTO/SSR applications.

All Gen IV engines feature the camshaft position sensor up front, at the timing cover. The camshaft position sensor part number for Gen IV 4X cam gears is 12591720. This cam position sensor applies to LS2, LS7, LS3, and LS9 applications. If you need a camshaft position sensor harness (doing a swap, etc.), the GM part number is 12627501.

An easy way to identify a Gen III versus a Gen IV is the location of the camshaft position sensor. If the sensor is mounted at the timing cover, it’s a Gen IV engine.

Lifters and Lifter Guides

In an LS engine build, you have two choices of lifters: OEM or aftermarket. OEM-style lifters must be guided within an OEM plastic guide. Aftermarket performance lifters are connected in pairs via a pivoting tie-bar link.

Factory plastic lifter guides provide a register feature: the lifters have opposing flats on the upper body that register into flats in the plastic guides. This style is certainly adequate to maintain the lifter roller bearings in plane with the cam lobes. While flat-tappet lifters are designed to rotate in their bores during operation, roller lifters must remain in a fixed plane to allow the roller bearings to roll against the cam lobes. If the lifter rotates a bit, the rollers may tend to skip and chatter along with cam lobes. A superior approach is to use high-quality aftermarket roller lifters that are tied together in pairs with a pivoting link bar. This style provides a much more precise design that keeps the lifter rollers in plane with the cam lobes.

Over time, age and wear to the plastic guides may allow the lifters to slightly rotate out of plane; perhaps not enough to destroy a cam but enough to reduce efficiency and the long-term durability of both the lifter roller and the cam lobe. For maximum performance and durability, linked tie-bar lifters are a superior choice, especially when you’re chasing maximum performance and sustained high engine speeds. In short, if you’re planning to slam the engine for all it’s worth, get rid of the factory plastic guides and factory-style lifters and upgrade to tie-bar roller lifters.

If you’re using the OEM plastic lifter guides, be aware that excess oil tends to puddle at the floor of each lifter’s location. For faster oil drainback, drill about a 5/16-inch diameter hole at the outboard side of the guide, just above the floor at each lifter location. The outboard side is the one that faces the exhaust side of the engine. After drilling the holes, carefully deburr to remove any plastic fragments, then wash and clean to make sure that the guide is free of debris.

If you’re using aftermarket roller lifters that are connected in pairs with a tie bar, you have no need for the OEM plastic lifter guides. The purpose of using OEM guides or tie-bar lifters is to maintain the lifter rollers in plane with the camshaft lobes. Unlike flat-tappet lifters that are designed to rotate during operation, roller lifters must be locked in plane to prevent rotation, allowing the lifter roller tips to roll against the lobes. If a roller lifter rotates in its bore, the lifter will crash and scrub against the lobe, resulting in very quick and catastrophic damage to both the lifter and cam lobe.

CAMSHAFTS AND LIFTERS

Note that due to the design of the LS block and cylinder heads, lifters may be installed or removed only with the cylinder heads and head gaskets removed. Unlike early generation small-block engines that allow lifter access by removing the intake manifold, gaining access to LS lifters requires removal of the heads and head gaskets.

High-performance roller lifters are available individually to use with OEM plastic lifter guides or as tie-bar-connected pairs that eliminate the need for the plastic lifter guides. The only downside of using tie-bar roller lifters is that during a camshaft change, the lifters must be removed in order to reach the cam. The plastic lifter guides allow you to pop the lifters up and away from the cam lobes without the need to remove the lifters. With the rocker arms and pushrods removed, by rotating the crankshaft twice, the lifters are pushed up into the “locking” position where they are slightly gripped by the guides, holding the lifters up and out of the way. However, not having that feature is a small price to pay for the advantage of the extremely durable tie-bar roller lifters that are available in today’s aftermarket.

When securing the OEM plastic lifter guides, the OEM 6-mm x 1.0 bolts must be used; they feature a shoulder under the bolt head that properly registers the lifter guide to the block. These bolts are tightened at 106 in-lbs. Applying a drop of Loctite 242 blue thread locker isn’t a bad idea.

Lifters guides, also referred to as lifter buckets or lifter trays, tend to collect excess oil at the outboard sides. It’s a good idea to drill a 5/16-inch hole at the lower outboard side of each bank to allow better drainback.

While factory LS cams may feature a single-bolt or three-bolt connection of the cam gear to the cam, the majority of aftermarket performance cams feature the three-bolt design.

Pictured here is a factory roller lifter from a 5.3L engine (left) and an aftermarket roller lifter for the same application. The performance lifter features a more robust roller bearing and heavy-duty bearing axle. Also notice the difference in overall length.

Install the camshaft retainer plate with new screws. ARP retainer plate screws are highly recommended. Apply a drop of medium-strength thread locker to each screw’s threads, and tighten to 18 ft-lbs.

Many performance builders prefer bronze lifter bushings, which provide superior lubricity for the lifter bodies. Installation requires overboring the lifter bores, press-fitting the bronze bushings, and machining the bushing inside diameters to provide lifter bore oil clearance, which is usually in the .0015-inch to .0018-inch range. Machining the lifter bores and sizing the bushing inside diameters should not be performed with abrasive honing stones, as this may result in inconsistent inside diameters along the length of the bushings. The preferred method is to machine with the appropriate cutters, either using a specialty fixture to obtain the correct geometry and bore angle or with the use of a CNC-machining center. This photo shows bronze lifter bushings installed in a World Products Motown II LS block, but the same practice applies to conventional LS blocks.

An aftermarket lifter may feature a deeper pushrod cup location. This is one more example of why it’s important to measure for pushrod length instead of assuming that factory-length pushrods will suffice.

High-quality aftermarket performance roller lifters feature stronger roller bearings and are available with larger-diameter rollers that help to increase duration. High-performance lifter rollers are designed to accommodate higher valve spring pressures and higher engine speeds while maintaining durability. The example shown here is a roller lifter from Morel, a firm that also supplies roller lifters to several performance aftermarket cam and valvetrain manufacturers.

Depending on the height of the boss, a V-style tie-bar link may be necessary to provide clearance.

Roller lifters that feature a tie-bar link are available with either a straight link or a V-shaped link. The V-shaped link is available to provide added clearance between the link and the block’s bosses in the lifter valley.

Roller lifters that are connected by a tie-bar link are able to cycle vertically in their bores, and the links are better than the OEM plastic lifter guides at preventing lifter rotation.

  Written by Mike Mavrigian and republished with permission of CarTech Inc

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In 2013, General Motors released the Gen V platform, which will eventually replace the LS-series engine in all platforms. The Gen V shares the look of the III/IV series, but in reality, it is all new. The biggest advance­ment in the LT-series is the use of direct injection, where the fuel is sprayed directly into the com­bustion chamber at high pressure (2,175 psi for the LT1), which aids in fuel economy and overall performance through better fuel atomization. Direct injection also makes cylinder deactivation more efficient, further increasing fuel economy. The 2014 LT1 Corvette can get as good as 29 miles per gal­lon (mpg). Other advancements include piston oiling jets, active fuel management, and continu­ously variable valve timing.

Because of the direct-injection method, the intake valves must be cleaned regularly—some sug­gest every 5,000 to 10,000 miles. This is performed with a spray-in additive while the engine is run­ning. If this is not done, the intake valves get gunked up, caus­ing serious drivability issues. This is the nature of direct injection.

The LT5 engine has a sec­ond set of injectors in the intake above the intake valves. This eliminates the need for the clean­ing agent, but all other LT-series engines need this process. A rule of thumb is to clean them at every oil change to make sure that you don’t forget. It is a required service at least every 25,000 miles, which is three oil changes because Gen V engines have a recommended oil-change interval of 7,500 miles. This is preventative maintenance to eliminate the larger expense of a top-end rebuild.

LT Car Engines

Chevrolet Performance cur­rently has three crate versions of the Gen V: a naturally aspirated 6.2L 460-hp LT1 (the engine installed in the base-model C7 Corvette), the supercharged 6.2L 650-hp LT4 (the engine in the Z06 version of the C7 Corvette), and the LT376, the newest LT-series crate engine that is essentially a hopped-up naturally aspirated LT1 with GM’s high-lift LT1 Hot Cam and CNC-ported heads, gen­erating 535 hp on a base tune. The LT1 for Camaros is rated at 455 hp.

Most swappers procure factory-installed engines. These powerplants have been installed in GM trucks and SUVs begin­ning in 2014 (1500 series only) as well as Corvettes and Camaros. The 4.3L LV3 Ecotec V-6 is the 6-cylinder variant of the LT-series, which is available in 1500-series GM trucks as well.

6.2L LT1

Making 460 hp without a supercharger is not easy, and to do so while hitting 29 mpg is even harder, but the LT1 does exactly that. The 4.06-inch bore combined with the 3.62-inch stroke creates an 11.5:1 compres­sion ratio, which makes efficient use of the fuel pumped through the direct-injection nozzles. A forged crank, hypereutectic pis­tons, and forged powdered metal rods yield light weight and dura­bility. The heads are conven­tional aluminum castings and feature lightweight sodium-filled valves. There two oiling systems available: a wet sump and a dry sump.

6.2L LT4

To pump up the output of the LT1, General Motors dropped a supercharger onto the 6.2L block to make 650 hp. To make that work long-term, some changes were made to the rotating assem­bly. The crank is the same, but the rods were slightly redesigned to increase strength in key areas. The pistons in the LT4 are forged, and the combustion chamber was opened up, decreasing the com­pression ratio to a boost-friendly 10.0:1. The heads are rotocast, making them stronger and better at handling higher heat ranges. The valves are solid titanium, and the oiling system is a dry-sump design, same as the LT5, and is an option on the LT1.

6.2L LT5

In late 2017, General Motors announced the release of the new­est version of the Gen V LT-series engine: the LT5. This is a super­charged V-8 that is similar to the LT4, except this monster motor uses a higher-output supercharger and a redesigned crankshaft and new fuel injection system to gen­erate 750 hp and 715 ft-lbs of torque. The most powerful GM production engine is slated for installation in the 2019 Corvette ZR1. The oiling system is dry sump only.

Gen V Truck Engines

Beginning in 2014, all GMC/ Chevrolet trucks, vans, and full-size SUVs with V-8 gaso­line engines came with Gen V engines. There are currently three truck versions: the LV3 4.3L (LT-based V-6), the L83 5.3L V-8, and the L86 6.2L V-8. The V-6 is an LT-series engine, essentially a V-8 with two cylinders cut off. The V-8s are the most common for trucks and SUVs.

4.3L LV3

A V-6 in a swap book? Some might balk at the idea of swap­ping a V-6 when they could swap in a V-8, but consider the merits of the 6-banger before writing it off. For starters, it is an LT engine with two cylinders lopped off, just like the previ­ous 4.3L V-6, which was based on the second-gen model (also named LT1, coincidentally). The LV3 features 11.0:1 compression with 99.6-mm bore on a 92-mm stroke, maxing the RPM at 5,800. It uses a forged steel crank with powdered metal connecting rods and caps, just like the rest of the Gen V LT family.

With 285 hp and 305 ft-lbs of torque, this diminutive power­plant has the potential to make 400 hp with minor upgrades. It could easily reach 350 hp with just a simple tune. The V-6 plat­form has a smaller block, which provides more options for swap projects. Fitting this 6-cylinder into say an MGB is much easier than the V-8 version, and it can make almost as much power. The fuel economy on the LV3 is 18 city, 24 highway in trucks that weigh upward of 6,000 pounds. Drop that into a 2,500-pound Euro sports car, and the economy will be substantially better.

5.3L L83

This engine features a 3.78- inch bore, 3.62-inch stroke, and 11.0:1 compression ratio. These engines make 355 hp and 383 ft-lbs of torque with gas, while E85 produces 376 hp and 416 ft-lbs. Readily available from most salvage yards, these engines are not yet in demand because they are so new. Prices are currently under $2,000 for a complete L83, and the ECM and fuel-pump modules are inexpensive too. Once these models begin wearing out engines and the swap market picks up, the prices will go up. An LT-based engine will be cheaper than an LS Vortec, and the LTs have fewer miles.

In 2014, the LT1 stormed onto the scene in the Corvette. This 460-hp beast features direct injection, where the fuel is sprayed directly into the combustion chamber, ensuring adequate combustion. The science behind how this works is fascinating. There was a lot of interest in swapping these engines, but the fueling system kept the swaps from taking hold at first. (Photo Courtesy General Motors)

General Motors quickly released the LT4, a super­charged version of the LT1. Basic changes were lower-compression heads (down from 11.5 to 10:1) and a big supercharger. The LT4 is good for 650 hp in stock tune. (Photo Courtesy General Motors)

Because everyone needs more horsepower, General Motors created the LT5. This beast adds 100 more ponies over the LT4, for a total 750 hp and 715 ft-lbs of torque. The last C7 Corvette, the ZR1, received this engine in 2019, and it is now available as a stand-alone crate engine. (Photo Courtesy General Motors)

While most would dismiss a V-6, the LT series has a V-6 in the lineup, and it is pretty impressive in its own right. It is 285 hp stock; a tune would easily take it to 350; add a turbo, and it could probably get into the 500s. Plus, it is small and lightweight, so it can fit in cars where a V-8 won’t. This engine is found in GM trucks and vans. (Photo Courtesy General Motors)

General Motors rolled out the LT series right away in all trucks and SUVs with the L83 5.3L V-8. Having 355 hp and extremely good fuel economy make this a great engine for a swap. There are tons of them out there in low-mileage wrecked trucks. (Photo Courtesy General Motors)

You can’t leave all the fun to the cars, so General Motors dropped the L86 6.2L V-8 into the high-end Denali and High Country truck models, and in 2018, the company began offering them in the high-end SUVs as well. At 420 hp with pull well into triple digits, these 6.2L L86s can do impressive things in a 6,500-pound truck. Capa­ble of low-14-second quarter-mile times and a blistering 5.4-second 0–60 time, the L86 6.2L engines are more than capable. They are harder to find, and cost more, but they are worth every penny. (Photo Courtesy General Motors)

6.2L L86

The L86 is a modified LT1 that makes 420 hp and 460 ft-lbs of torque. The LT1 and L86 are very similar down to the compression ratio of 11.5:1. If you want any of the larger 6.2L Gen V engines, you are going to pay for it, but not as much as a 6L LS will cost. Current prices are in the $2,500 to $5,000 range for an L86 from a low-mileage wreck.

Fuel economy from the L86 is quite impressive as well. GM trucks with this engine often see 22–25 mpg on the highway, which is incredible for trucks weighing in at 6,000-plus pounds. In my personal 2015 GMC Denali 1500, a 25-mile best of 34.7 mpg was recorded. This was under perfect conditions and in a slight down­hill stretch, but it happened, and it was spectacular. The physical differences between the LT1 and the L86 are: the intake (the L86 intake is larger and makes more torque), the exhaust system, and there is the optional dry-sump oiling system for LT1s. The extra 40 hp comes from tuning and the intake. They even share the same camshaft.

Engine-Swap Projects

The goal of this book is to assist in an LT-series engine swap. Whether swapping a 1969 Chevy truck, a 1970 Chevelle, or a 1999 Miata, the information in this book will help you achieve your goals. Performance is typi­cally the number one goal of any engine swap, and the LT-series offers that in spades. As these engines become more popular, the aftermarket is rapidly pro­ducing more performance com­ponents. Spicing up an LT engine is almost as easy as ordering the parts themselves.

The main concerns for LT swaps are fitting the oil pan, acces­sory drive, power steering, and fuel system. Another issue is the exhaust (mainly headers or man­ifolds) because the head design for LT engines is different from the LS series, and there are simply not very many options for swaps, so you need to get a little creative. Luckily, there are more options now than there were six months ago, so by the time you read this book, there will be even more options available for your LT swap.

This Tech Tip is From the Full Book, HOW TO SWAP GM LT-SERIES ENGINES INTO ALMOST ANYTHING. For a comprehensive guide on this entire subject you can visit this link:

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Locating an LT engine is as simple as ordering a crate engine from a dealer, parts house, or local salvage yard. There are distinct differences between the car and truck engines. All truck engines have a longer crank pulley, which is because the truck engines use an engine-mounted belt-driven vacuum pump for the brake assist. Additionally, the truck engines use a driver-side biased water pump (all LT pumps are off­set), while the car engines use a passenger-side offset pulley. This is not a big deal for most appli­cations, but the accessory drives can’t be interchanged without swapping all of it.

Swapping Problems

The LT-platform has tons of potential for increased perfor­mance, but there are some caveats that must be addressed for swaps. The main issues are the fuel sys­tem and the lack of a power steering pump. Both of these are addressed at length in the pages of this book, but it is something that you need to know going into planning an LT swap.

Nearly every new vehicle uses electric power steering. This reduces drag on the engine and gives the manufacturer the abil­ity to tune the steering assist based on vehicle speed. There are options for aftermarket elec­tric power steering, such as with American Powertrain, otherwise an aftermarket accessory drive can be used on an LT engine to have traditional power steering. This is the main reason that Gen­eral Motors is not using the LT engine in the larger 2500- and 3500-series trucks. These vehicles use a hydroboost for the braking system, and they simply need to have a power steering pump to provide the hydraulic pressure for the hydroboost.

The fuel system is the other major departure from the tradi­tional swap. LT engines are direct-injected, which uses a PWM fuel pump without a return line to feed the engine with up to 76 psi of fuel pressure. From there, the engine further increases the fuel pressure with a mechanical fuel pump. The chassis or tank pump is therefore a lift pump, essentially moving the fuel from the tank to the engine. The complexities of the fuel sys­tem are addressed in chapter 8.

Outside of these two areas, an LT swap is fairly simple. There are some notable differences from other engine platforms, but that is to be expected. The rest of this book deals with how to perform a swap and covers most of the details. While every car and swap are different, there are quite a few common aspects.
Swapping an LT engine into just about anything is not the most complicated automotive endeavor. An average swapping project is fairly easy if it is care­fully conceived, researched, and planned. The Gen V LT engine shares a similar footprint with the original small-block Chevy. The general rule of thumb is that if a small-block fits, an LT will fit as well, with some minor adjust­ments of course. Engine position, oil pan, and accessory drives are the most common physical fit­ment issues.

Unlike previous fuel-injected engines, there is no carbureted option for LT-series engines. The nature of direct injection pre­vents the possibility of using a carburetor. This means that every LT swap requires using an electronic control module (ECM) and sensors. In most cases, you must carefully modify the wiring harness, plugs, and wiring, or purchase the correct aftermarket components for plugging in the particular engine to a specific car. Chevrolet Performance, Howell EFI, HP Tuners, and many others offer products and tuning that make swapping the electronics much easier. In the end, you get a more efficient powerplant with the ability to tune it better and faster.

one of the most affordable ways of procuring a GM LT-series engine is through a salvage yard. Because these engines are so new, the demand is quite low, but people wreck trucks every single day. When a new truck is totaled, it goes to a salvage yard. While body panels and interior pieces are in demand for repairs, the drivetrains are so new that there just are not very many on the road with enough miles on them to break down. In fact, many of these vehicles are still under warranty. This means the market is in the prime position to buy low-mileage LT-series engines at a substantial savings. Within the next five years, the price of these engines will go up considerably.

If you have never purchased a salvage engine, you may be a little leery of the process. While you can certainly be taken advantage of, the more you research, the better off you will be. There are several keys to successfully buying a salvage engine: knowing where to buy, knowing what you are buying, and finding what parts are available.

Where to Buy

Knowing who you are buying from is just as important as knowing what you want. The internet is a glorious tool for helping weed out the undesirable salvage yards that take advantage of their customers. Salvage yards often have a reputation for being sleazy, and those certainly still exist, but the more-reputable yards get better reviews online, helping you make a more informed decision on where to buy. There are some salvage yard networks, such as LKQ, that link qual- ity yards together so that you can find the parts you need from all over the country.

Then there is the pull-a-part-style yard, where you remove the parts that you need. These yards are usually less expensive.

However, you need to research the parts, find the vehicle, and remove the parts using your own tools. Some yards pro- vide cherry pickers or forklifts to remove large parts, such as engines, while others do not. That is the caveat emptor of salvage yards: research the yard and ask questions.

Know What You Are Purchasing

Purchasing a used engine means dealing with a shop or salvage yard that has dismantled a vehicle. When it comes to engines, most yards want to get the job done as quickly as possible and break the vehicle down to as many sellable parts as possible. This means that for most engines, the wiring harness gets chopped along with the fluid lines. Most yards remove the peripheral components, including the throttle body, alternator, starter, and air-conditioner compressor. Some yards strip engines to the long-block, meaning no intake, exhaust manifolds, or water pump as well. It pays to ask what comes with the engine when you are researching your purchase. You might pay an extra hundred or two for a complete engine, but buying the peripheral components can cost thousands in the end.

If at all possible, get the ECM and throttle pedal from the same vehicle. It is not absolutely critical, but it is nice to know everything is already paired together.

Get the Vehicle Information

Because there are some key differences in the engines themselves, you need to know where your engine came from. While the original vehicle’s vehicle identification number (VIN) is not as important, get the year, make, and model of the vehicle, along with the original mileage. There are small differences between year, make, and model for each engine, and you need that information readily available for future service.

Parts That Are Available Buying a used engine, whether it is from a salvage yard or a private seller, typically means you are getting part of the package but not the complete package. With LT engines, you need the engine, throttle body, throttle pedal, ECM, wire harness, fuel control module, and accessories. If you can source this all from the same vehicle, that is perfect, but if not, you need to match the components from a similar vehicle and engine.

A V-6 throttle body is different from the 5.3L L83, and the 6.2L L86/LT1/4/5 engines use a different throttle body than the smaller Gen V engines. You can convert to the larger throttle body, but swapping a 5.3L throttle body to a 6.2L will decrease performance. The ECM, fuel modules, and wiring harnesses are the same for the truck engines.

As with any purchase, the more you can research on the seller and the parts you are buying, the better off you will be. Keep in mind that any used engine is just that—used. There are no warranties from General Motors, but many salvage yards offer short-term warranties and even extended warranties that can be a great benefit, which is just one more aspect to consider when shopping for a used LT engine.

When ordering a crate engine, this is what you get: a big box on a pallet. You will need a forklift or pallet jack. This LT1 crate engine was ordered with the complete ECM control package and was installed in the 1971 Buick GS seen in this book.

Inside the crate is a brand-new $8,500 to $10,000 engine, all shiny and clean. Don’t want to spend that much? There are other options. Want to spend more? The LT5 is now available as a crate engine, and you can also order a complete drivetrain with the ECM, transmission, and all the controllers, harnesses, and other components needed for the drivetrain itself. This does not include the fuel system, mounts, or accessories.

This is what $1,500 will get from just about any larger salvage yard: an engine without any accessories or wires. We scored this one from LKQ, a national chain of salvage yards, for $1,575 with free shipping because it was local. You don’t get the throttle body, and usually you don’t get the exhaust manifolds either. We were lucky. This take-out engine found its new home in a 1987 Camaro built for this book.

Salvage yards leave the harness plugs attached. Most of the time you can’t get a salvage harness, because it takes too long to strip it out, so they just chop the wires. We have tried requesting a used harness, but they always tell us they won’t do it. This varies yard to yard. All the sensors are there.

Written by Jefferson Bryant and republished with permission of CarTech Inc

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Boost is really nothing more than a power multiplier. When I add boost from a turbo to a typical 430-hp LS3, it is important to understand that the NA LS is already running under boost, which comes courtesy of the atmosphere and equates to 14.5 psi at sea level. This atmospheric pressure obviously changes (as does the power output) with alterations in things such as elevation, temperature, and humidity, but the mechanics do not. As the piston races downward with the intake valve open, the external positive atmospheric pressure forces air into the negative pressure created by the piston.

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This scenario creates plenty of power potential as you increase the external pressure applied to the engine above atmospheric. If an LS3 produces 430 hp at an atmospheric pressure of 14.5 psi, then you can theoretically double the power out­put (to 860 hp) if you supply an additional 14.5 psi of boost pressure. In truth, there are a number of rea­sons why this power/boost formula doesn’t always work, but it is none­theless a good indicator of potential power from a turbo engine.

Another great thing about the formula is that it can be applied at any given boost level. If you apply just 7.25 psi (.5 bar or 50-percent atmospheric pressure), you get a corresponding 50-percent increase in power (430 to 645 hp). The same goes for running 10 psi (430 x 1.689 = 727 hp), or even 2 bar (29 psi), where your 430-hp LS3 becomes a 1,290-hp monster. This example illustrates the importance of combining a powerful NA combination with boost because the power gains are simply multiplied by the original output. The more you start with, the more you finish with. Having more power to start with also allows you to reach any given power level at a lower boost level.

Although the boosted power output is a function of the origi­nal power multiplied by the boost (actually pressure ratio), know that all boost is not created equal. The advantage turbochargers have over superchargers is that very little power is required to drive the compressor of the turbo. The impeller or rotors of a supercharger are driven directly off the crankshaft. This mechanical cou­pling can provide immediate boost response, especially with positive dis­placement superchargers. However, as with the power steering, A/C, and alternator, the parasitic losses asso­ciated with driving the supercharger reduce the power output offered by the engine. This means that for nearly any given boost level, the turbo should produce more power than a comparable supercharger.

This power differential increases with boost (and flow), but know that 10 psi from a supercharger does not produce the same power curve or output as 10 psi from a turbo. The sacrifice for this efficiency can be boost response, but proper sizing can produce amazing results because factory turbo engines are able to pro­vide peak boost pressure as low as 1,800 rpm (lower than you would want for almost any performance application).

Turbos have offered this type of performance since their inception, but one of the major reasons for a sudden surge in popularity is avail­ability. Like it or not, the advent of affordable, offshore products has helped create the current turbo craze. Before the China connection, turbo kits were few and far between, pri­marily because of their expense. The average Joe could not or would not spend $5,000 to $6,000 on a turbo kit, but thanks to knock-off turbos, intercoolers, and the associated cou­plers and tubing, turbo pricing has dropped dramatically.

Obviously it pays to shop wisely, but putting together your own turbo kit can be done for less than half of what it cost not long ago and even less if you shop around. With $300 to $400 turbos, $125 intercoolers, and aluminum tubing bends read­ily available, it is possible to piece together a DIY turbo system for less than $1,000 if you start with fac­tory exhaust manifolds. This type of kit is not going to put a scare in the Street Outlaw boys, but it is capable of boosting the power of an LS by 50 to 100 percent or more.

Another area where supercharg­ers and turbochargers sometimes dif­fer is in the intake manifold design. Turbos and centrifugal superchargers tend to use the factory (or equiv­alent) long-runner intake design. Positive displacement supercharg­ers often replace the factory mani­fold to mount the blower. Primarily for packaging reasons, the super­charger is combined with some type of ultra short-runner intake because it is often difficult to get the super­charger, intercooler, and intake man­ifold under the hood of your average Camaro or Corvette.

There is some merit to the fact that the immediate boost response overcomes the torque losses (from charge filling) associated with opti­mized runner length, but using long-runner intakes is one advantage turbos (and centrifugal supercharg­ers) have over positive displacement superchargers. As indicated in Chap­ter 1, runner length is one of the major factors that shape the entire power curve. Even on turbo appli­cations, selecting the correct runner length tunes the combination to the desired engine speed. If you want your turbo LS3 or LS7 to run well up to 6,500 rpm, stick with a stock, FAST, or MSD Atomic intakes. If you are looking to elevate engine speeds, short-runner intakes such as the Hol­ley Hi-Ram can push power produc­tion on a turbo engine past 7,000 rpm.

When it comes to turbochargers, size really does matter. Like cam timing and intake manifold design, turbos should be selected to maximize power over a given RPM range, balancing response rate with ultimate boost and power potential.

The heat generated by turbo systems needs to be managed properly. Make sure to shield components positioned near the exhaust system.

Whether running a supercharger or turbocharger, intercooling is an effec­tive way to improve power and elimi­nate harmful detonation.

Because they control the boost pres­sure supplied to the engine, make sure to purchase quality waste gates such as this unit from Turbo Smart.

Test 1: Effect of Ignition Timing on a Turbo 4.8/LS3 Hybrid

Nothing wakes up an NA engine like a small dose of boost. The critical element when running boost is actually making sure the air/fuel and timing values are correct because a turbo engine runs thousands of trouble-free miles when treated to the proper tune. Typically, turbo engines require additional fuel and a slightly richer mixture than its NA counterpart. For maximum (safe) operation, an NA engine is typically tuned to achieve an air/fuel ratio near 13.0:1. By contrast, a turbo engine runs its best and is safer with a richer air/fuel ratio closer to 11.5:1. It is possible to run the turbo engine leaner than 11.5:1, but this is an effective air/fuel mixture for safe operation.

In terms of ignition timing, an NA engine runs best with more total timing than a forced-induction application. A good strategy is to have a drop of 1/2 to 1 degree of total timing per pound of boost. For the 6-psi application, this means a decrease of 3 to 6 degrees of total timing, but the actual amount is dependent on available octane.

To illustrate the power gains offered through changes in timing on a turbo LS, I installed a single Precision turbo on an LS3 equipped with a 4.8 crank. The turbo kit used a set of JBA headers feeding a custom Y-pipe equipped with a T4 turbo flange. The package also included a Turbo Smart wastegate, air-to-air intercooler, and 114-octane Rocket Brand race fuel. Set to run just 6 psi, the combination of the intercooler, safe air/fuel mixture, and race fuel allowed me to safely dial up the ignition timing.

Running 18 degrees of total timing, the turbo LS produced 539 hp and 502 ft-lbs of torque. Stepping up to 20 degrees resulted in 551 hp and 507 ft-lbs; 22 degrees brought 557 hp and 517 ft-lbs. The final test at 24 degrees resulted in 575 hp and 523 ft-lbs of torque. Each step up in timing brought additional power, but there is a limit to how far you can go with the available octane, and the timing increased peak torque less than peak power (less timing is required at the torque peak than the horsepower peak).

Precision supplied a 67-mm turbo for this low-boost test.

Optimizing ignition timing is important for an NA LS application, but it is critical on a turbo engine.

Increasing the total timing from 18 to 24 degrees increased the power output of the turbo LS from 539 to 575 hp. This shows the importance of ignition timing on a turbo application, but don’t get greedy or you will just as quickly ruin a perfectly good engine.

The change in ignition timing offered serious power gains on the turbo hybrid engine (actually all turbo engines). The additional ignition timing was more beneficial at higher engine speeds (typical for timing), but the torque gains were sizable as well. Care must be taken not to add too much timing because detonation can rear its ugly (and destructive) head. Running just 6 psi on race fuel and with an efficient intercooler allowed me to maximize timing on this turbo engine.

Test 2: 6.0 LS3 Hybrid: NA vs Single Turbo at 6.8 and 9.8 psi

This test involved turbocharging and applying boost to an LS hybrid. The hybrid was built by combining a 6.0 bottom end with an LS3 top end. The 6.0 short-block was boost-ready thanks to a forged rotating assembly that included a SCAT crank, K1 (6.125) rods, and JE Asymmetrical pistons. I combined a flat-top piston with the 70-cc combustion chambers for this turbo combination. The 6.0 hybrid was assembled using Fel-Pro MLS head gaskets and ARP head studs. Although I ran a number of cams on this combination, this test was run with a stock LS2 cam. The stock LS3 heads were treated to a valve spring upgrade from BTR. I also ran 75-pound FAST injectors, the stock LS3 intake, and a FAST (manual) throttle body.

In essence, this 6.0 was an LQ9 or LS2 equipped with high-flow LS3 heads. Run on the dyno with a Holley HP Management system, long-tube headers, and a Meziere electric water pump, the LS produced 480 hp at 6,000 rpm and 472 ft-lbs of torque at 4,800 rpm. After adding the single turbo kit that included a Precision turbo (PN PT6766), CX Racing ATW intercooler, and Turbo Smart wastegate, I applied boost to the hybrid. Running 6.2 psi (6.8 psi at the torque peak), the turbo-hybrid produced 615 hp and 619 ft-lbs of torque. After stepping up to 9.8 psi, the power output jumped to 718 hp and 687 ft-lbs of torque. The increase in boost improved power production through the entire rev range.

This hybrid started life as a 6.0 truck engine but was upgraded with JE pistons, K1 rods, and a SCAT crank. For this test I retained the stock LS2 cam.

The changes in ignition timing increased the power output of the turbo test engine by 36 hp.

This test shows that even small amount of boost can have a dramatic effect on power production. Equipped with a 6.0 short-block, stock LS2 cam, and LS3 heads, the NA hybrid produced 480 hp at 6,000 rpm (as high as I revved it during the test). After adding the single Precision turbo, power jumped first to 615 hp at 6.2 psi (6.8 psi came at the torque peak) then to 718 hp at 9.8 psi. There was still more power to be had from the turbo, but this test wasn’t designed to max out the engine or turbo.

The torque gains offered by the single turbo were impressive. Although the engine dyno artificially loaded the engine to provide a better boost curve than you might see on the street or strip, adding 6.8 psi (actually just 6.2 psi at the peak) of boost increased torque production from 472 ft-lbs to 619 ft-lbs. Adding another 3 psi pushed the torque peak to 687 ft-lbs.

Test 3: Turbo Cam: LS9 vs BTR Stage II 4.8/LS3 Hybrid

The right cam is critical for any LS turbo application, including the short-stroke hybrid used for this test. Typical LS3 applications combine a 4.065-inch bore with a 3.622-inch stroke. This 6.2 combination works well and accommodates turbocharging. The combination used for this test replaced the stock 3.622-inch stroke with a smaller 3.267-inch stroke from a 4.8. With the exception of the smallest (4.8) and largest (7.0) engines in the family, all other LS engines (5.3, 5.7, 6.0, and 6.2) share the same stroke crank. The 4.8 shared the block with the 5.3, but the reduced displacement came from a shorter stroke. For this test, I combined the 4.8 crank with custom Lunati rods and forged JE pistons then stuffed it all inside an LS3 aluminum block. I then topped it off with a set of TS Gen X 255 heads and Holley Hi-Ram intake.

The turbo system consisted of a single 76-mm turbo from Precision Turbo fed by a pair of DNA turbo manifolds into a custom Y-pipe. Controlling the boost was a pair of Turbo Smart waste gates. Boost was fed through an air-to-water intercooler from CX Racing. This test was a comparison between the most powerful factory cam (LS9) and a Stage II turbo cam from BTR. The boost was limited to a maximum of 9 psi using just the waste-gate springs (no controller).

Run with an LS9 cam, the short-stroke turbo engine produced 701 hp and 598 ft-lbs of torque. The boost curve (on the spring) started at 8.5 psi, rose to a maximum of 9.4 psi, then dropped to 8.0 psi. After swapping in the BTR Stage II cam, the power output jumped to 733 hp and 621 ft-lbs of torque. The boost curve started at 8.2 psi, rose to 8.9 psi, then dropped to 8.0 psi. The BTR turbo cam improved peak power and offered more than 60 ft-lbs lower in the rev range.

Feeding the short-stroke turbo engine was a Holley High-Ram intake and TFS Gen X 255 heads.

What looks like an LS3 with forged pistons was actually a 4.8/LS3 hybrid. The aluminum LS3 block was stuffed with a 4.8 crank, custom Lunati rods, and JE forged pistons to produce a (high-RPM) short-stroke LS3.

The great thing about the BTR turbo cam was not just that it added 34 hp, but that it improved the power output through the entire rev range. More peak power is good, but more power everywhere is even better!

We all love big horsepower gains but torque is more meaningful in real-world street driving. In addition to adding 34 hp, the Stage II BTR cam dramatically improved torque production over the LS9 cam. Down low, the BTR cam offered as much as 62 ft-lbs of torque, which is a sure indication that the BTR guys understand the needs of a turbo LS engine.

Test 4: Turbo Sizing: Big vs Small 76-mm

Turbocharging has been around since the birth of the internal combustion engine because it is a tried-and-true method of improving the power output. The basic concept is to force-feed the engine more air than it would ingest of its own accord. This air contains power-producing oxygen molecules, which when combined with fuel, ignite to provide the downward force on the crank. More air equals more oxygen, which in turn equates to engine power. Of course, this assumes the turbo is sized correctly for the intended application and desired power level. This also assumes you have sufficient fuel flow to meet the needs of the engine, something I neglected to do on this test (the results nonetheless demonstrate proper turbo sizing).

The 417 stroker test engine featured forged internals from Speedmaster and JE, along with an aluminum LS3 block from Gandrud Chevrolet. Topping the stroker was a FAST LSXR intake and throttle body, but I could only get my hands on a set of 60-pound injectors in time for testing. This ultimately limited the maximum power output, but the effect of turbo sizing was still clearly evident.

The 417 stroker was configured with a single turbo kit that consisted of a pair of tubular headers feeding a common Y-pipe. The Y-pipe was equipped with a pair of 45-mm Turbo Smart waste gates to control boost. The Y-pipe also featured a T4 turbo flange to readily accept a T4 turbo.

For this test, I ran a pair of T4 76-mm turbos, one from CX Racing and one from Precision Turbo. Although both advertised at 76 mm, the Precision unit was capable of supporting as much as 1,200 hp, and the CX turbo topped out under 800 hp. It bears mentioning that there was a substantial price difference between the two turbos ($450 to $1,800).

Run with the smaller CX turbo feeding an air-to-water intercooler, the turbo managed to produce just 7.3 psi at the power peak of 761 hp. The boost pressure rose as high as 9.9 psi early on, but fell off rapidly as it ran out of flow. The larger Precision turbo suffered no problem, but available fuel flow limited boost to just 12.5 psi, whereas the turbo stroker produced 913 hp and 925 ft-lbs of torque. The CX turbo would be great for a lower power level on a stock or mildly modified engine, but if you plan to crank up the boost on a stroker, better get the good stuff.

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The test engine was a 417 stroker that included a Speedmaster 4.0-inch stroker crank and rods with a set of JE forged pistons. The stroker assembly was stuffed inside a new aluminum LS3 block from Gandrud Chevrolet.

A pair of ported LS3 heads from TEA feed the LS3 stroker. The heads were combined with a custom cam from BTR.

Despite the lack of fuel flow, the graph shows gains offered by proper turbo sizing. Both are designated 76-mm turbos, but the Precision turbo offered significantly more flow than the unit from CX Racing. The boost pressure and power curve fell off rapidly at the top of the rev range with the smaller turbo.

The falling boost curve is even more apparent in the torque curves because the fall off in torque is even more pronounced. The smaller CX Racing turbo was about maxed out at 761 hp, but it managed to increase torque production by 260 ft-lbs over the NA engine. The Precision turbo was up more than 100 ft-lbs and only fuel flow kept me from easily eclipsing the 1,000 ft-lbs mark.

Test 5: Effect of Boost on a Turbo LSX B15 (14.6 vs 19.5 psi)

Boost from a turbo can be both a blessing and a curse. The blessing comes in the form of additional power because each extra pound of boost brings with it a substantial jump in power. The curse comes from the extra power as well because owners often become greedy after sampling all that wonderful power. If some boost is good, then more must be even better, right? Well, there is a limit to just how much fun is available without something getting hurt. The important point here is, don’t get greedy.

This test was run on a GM B15, boost-ready crate engine from Gandrud Chevrolet. Equipped with forged internals and LSX LS3 heads, the crate engine was perfect for this boost test. Because the B15 came with an intake manifold, I installed a Holley Hi-Ram intake and FAST 102-mm throttle body, along with Holley 120-pound injectors. Tuning for the turbo combo was controlled by a Holley Dominator EFI system

The key to a successful turbo engine is knowing its limits. The tune is important, especially at elevated boost levels. Forged internals are slightly more forgiving in terms of detonation, but even the toughest components snap without the proper air/fuel and timing curves. I made sure to dial in the timing and air/fuel (kept constant for each boost level) using the Holley system.

Running the single Precision 76-mm turbo through the air-to-water intercooler, the turbo B15 produced 951 hp at 6,300 rpm and 891 ft-lbs of torque at 5,200 rpm. The boost curve started at 16.0 psi, rose to 17.5 psi, then fell to 14.5 psi at the power peak. I relied on a manual boost controller, but an electronic version would have kept the boost consistent. After cranking up the boost to 19.6 psi (at the power peak), the peak power numbers jumped to 1,083 hp and 979 ft-lbs of torque. Once again, the boost curve started out at 20.1 psi, rose to 22.7 psi, then dropped to 18.8 psi (19.6 psi at the power peak of 6,300 rpm).

Keeping things cool during testing was this single-pass, air-to-water intercooler from CX Racing. I ran dyno water through the core during testing.

Once again I relied on the single 1,200-hp 76-mm turbo from Precision.

Boost always has a positive effect on the power curve, and this test was no different. Cranking up the boost from 14.6 to 19.5 psi increased the peak power numbers from 951 to 1,083 hp.

The manual waste-gate controller did not allow me to dial in the boost curve precisely through the entire rev range. Since I was getting close to the maximum output of the single Precision turbo and the back pressure was escalating, the boost curve was not consistent through the rev range and therefore, the LSX with 19.5 psi spiked above 979 ft-lbs early in the run. Despite this fact, the change in boost offered some serious torque gains.

Test 6: 4.8 LS3 Hybrid: NA vs Single Turbo at 9.8 psi

This test proves that turbo boost can be applied to any LS3 combination, including a short-stroke engine. This short-stroke engine was used extensively with both cathedral and rectangular-port heads and ran safely to 8,000 rpm with a hydraulic roller cam (see Chapter 3). The hybrid was the result of combining a 4.8 crank with a big-bore, LS3 aluminum block. Gandrud Chevrolet supplied the new GM block and stuffed it with forged internals from Lunati and JE. The short-stroke LS3 was topped for this test with TFS Gen X 255 LS3 heads that flowed more than 380 cfm. I liked the fact that the TFS heads featured even smaller port volumes than the stock heads (good for reduced displacement). The engine also featured an ATI dampener and complete Moroso oiling system (both critical at high RPM). Tuning came from a Holley EFI management system controlling 120-pound injectors.

For this test, the LS3 hybrid was equipped with a factory LS9 cam. (For details on how much a turbo cam might be worth, see Test 3 in this chapter.) The aluminum test engine was equipped with a single 76-mm Precision turbo capable of easily exceeding the intended power level for this comparison.

I ran the test engine in NA trim before subjecting it to boost. The hybrid produced 512 hp at 6,900 rpm and 415 ft-lbs of torque at 6,200 rpm. Credit the lack of displacement and Holley Hi-Ram intake for the elevated engine speeds (despite the mild cam timing).

Run with the single turbo system pushing out 8.5 psi at the power peak, the turbo-hybrid produced 701 hp at 6,500 rpm and 598 ft-lbs of torque at 5,500 rpm. Given the forged internals and 1,200-hp capability of the turbo, there was plenty more left in the combination, but this 700-hp turbo LS idled like a stocker and would provide thousands of trouble-free miles at this boost level.

Tuning for the short-stroke turbo engine was provided by a Holley Dominator EFI system. The Holley was used to control timing and fuel from the 83-pound Holley injectors.

The test engine was an LS3 aluminum block stuffed with a 4.8 crank, forged Lunati rods, and JE pistons. I topped it with a set of TFS Gen X 255 heads and Holley Hi-Ram intake. Note also the use of a Moroso oil pan and ATI dampener.

The NA short-stroke LS3 was no slouch at 512 hp, but things really got serious once I added boost. Running a peak of 8.5 psi, the turbo LS produced 701 hp, with plenty left in both the engine and turbo.

Despite the reduced displacement (compared to an LS3) and the use of a rather large 76-mm turbo from Precision, the boost response was very good and so were the torque gains. The boost increased torque production by as much as 192 ft-lbs, with consistent gains through the rev range.

Test 7: Turbo LS: Effect of Snow Water/Methanol Injection

You may be wondering why I decided to include a test on water/methanol injection in this chapter. In reality, water/methanol injection is a form of inter- cooling, which should be employed on any turbocharged (or supercharged) engine, almost regardless of the boost level.

Although the Snow Boost Cooler water/methanol injection does not provide additional power in the same way as (say) nitrous oxide, it does dramatically decrease the inlet air temperature. This combined with the extra octane offered in the methanol portion of the mixture allows you to be more aggressive on the ignition timing, air/fuel ratio, and/ or boost pressure to improve the power output.

The higher the intake charge temperature, the higher the risk of the fuel self-igniting. Having the mixture ignite prior to the piston being in the proper position can result in the expanding mixture working against the upward moving piston. At the very least, this has a detrimental effect on power production; at the very most, it can cause catastrophic engine failure.

In addition to minimizing the chance of detonation, a cooler inlet charge temperature can also provide additional power thanks to the increase in air density. Cooler air has more oxygen molecules per volume, so getting cool air to your engine should be considered mandatory. This is especially true of turbocharged (and supercharged) engines, where the compression (boost) has an elevated charge temperature well above ambient. In the case of the turbocharged LS running 8.5 psi of boost, the inlets air temperatures exiting the turbo exceeded 185 degrees. The Snow water meth system dropped the air temperatures to 95 degrees and improved power by as much as 29 hp and 32 ft-lbs of torque. Water/methanol injection is especially important when running pump gas because it allows for changes in timing and air/fuel that dramatically improve power (see Test 1).

This system featured dual nozzles, but I employed only minimal pressure and the smallest nozzle sizes on the low-boost LS.

The Boost Cooler from Snow Performance can be thought of as chemical intercooling. The injection of a water/methanol mixture dramatically cools the intake air temperature while decreasing the chance of detonation.

Adding the Snow Boost Cooler water/ methanol injection to the turbo LS dramatically decreased the inlet air temperature. The super-cooling system dropped the charge temps from 185 to 94 degrees at 8.5 psi of boost. This drop in temperature not only increases the power output, but allows for additional timing and changes in air/fuel to further improve power production.

Gains offered by the combination of the cooling effect and changes in timing were substantial on this turbo LS application. The changes in charge temperature would be even greater on higher boost applications. The Snow system netted an additional 29 hp and 32 ft-lbs of torque on this turbo LS.

Written by Richard Holdener and republished with permission of CarTech Inc

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Stock Blocks

Factory and aftermarket blocks are substantially different from one another. Factory blocks are mass-produced with wide tolerances permitted as “acceptable” for com­mon street applications. For exam­ple, while the factory specification for LS block deck height is 9.240 inches, OEM blocks rarely meet this spec. It’s rather common for a block to feature greater and/or lower deck height on any particular block, with deck height varying from low to high along either bank. This means that the decks may not be parallel to the crankshaft centerline. While this may not present a problem for the average street engine, if your goal is to obtain maximum power, decks must be checked and likely corrected to achieve the same cylin­der volume for all cylinders. Due to shifts in block geometry that result from the casting process, some cyl­inder walls may be thinner than others. The list goes on, but you get the point. If you wish to achieve maximum results for a power build, a factory block will likely require several corrective machining opera­tions to “accurize” the block.

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Unlike other LS blocks that feature powdered metal main caps, the LS7 comes from General Motors with steel-billet main caps.

The LS7 features pressed-in cast-iron cylinder liners that are the biggest cylinders in the LS lineup. The race pro­gram provided data that was used to develop a light, rigid block. The deep-skirt config­uration provides exceptional strength. The bulkheads hold six-bolt, cross-bolted main bearing caps that mit­igate crank flex. This is the front view of an LS7 block.

The LS2 features a 4.000-inch bore and a 3.622-inch stroke. In contrast to earlier Gen III blocks, the LS2 cylinder head bolt holes are blind and not open to water. Note the four-lug cam timing reluctor for the front-mounted cam position sensor on this cut­away of the LS2 6.0L aluminum block, deviating from the Gen III rear-mounted cam sensor.

The rear view of an LS2 block cutaway shows the bay-to-bay breathing openings at the bot­tom of the cylinders, typical of all LS blocks. The LS2 block is very similar to earlier blocks, with changes made to the cam position sensor location and blind head bolt holes.

In contrast, high-performance aftermarket blocks feature design enhancements such as thicker decks, stronger main webs, improved cyl­inder cooling, and improved oil­ing circuits, in addition to more precise CNC machining. Granted, a new bare block will need to be final-machined for the desired block deck height, lifter bore and cylinder bore diameters, and other dimensions. This final machin­ing is by design: The manufacturer provides extra material that allows you to custom-fit your specific com­ponents. In addition, aftermarket block makers provide much greater attention to detail in terms of raw machining, wherein crankshaft cen­terline, camshaft centerline, lifter bore spacing, and cylinder bore cen­terlines are already spot-on. While correcting an OEM block may force you to compromise in terms of cer­tain dimensions, with a quality aftermarket block you can obtain exactly what you want.

Even though factory blocks have been proven to handle drastic horsepower increases, such as builds configured with single or twin tur­bochargers that produce 1,000 hp and beyond, longevity and dura­bility are key issues. These blocks were not designed to withstand the level of high combustion pressures associated with such power levels. In my opinion, and in the opinion of many other engine builders, if you plan to increase power this dra­matically, upgrading to a stronger aftermarket block greatly reduces the risk of catastrophic failures that could result from excessive cylinder bore distortion and over-stressed main webs. If a build is planned to produce more than 700 hp, a stron­ger and beefier aftermarket perfor­mance block provides a much more reliable and stable platform for the build. Aftermarket performance and racing blocks feature thicker decks, stronger main webs, enhanced pri­ority main oiling systems, thicker cylinder walls, vastly improved bay-to-bay crankcase breathing, and stronger-grade materials in both alloy and iron configurations.

Modifying the Stock Aluminum Block

Modifying a stock block can involve both corrective and enhancement processes. It’s very common for stock LS blocks to have uneven and out-of-specification decks. While the spec deck height is 9.240 inches, you may find blocks that have slightly taller or shorter decks. In addition, LS factory blocks tend to be out of square, with the front or rear of the decks being shorter or taller than the opposite decks. The decks can be resurfaced to make them the same height and parallel to the main bore centerline, using the shortest area as the index. Making the decks parallel to the main bore centerline helps equalize the combustion area between the piston at TDC and the cylinder head combustion chambers, as well as equalizing pushrod length require­ments from cylinder to cylinder.

Performance aftermarket blocks usually provide a bit of extra deck height, allowing you to achieve the desired deck height. Finishing to the desired deck height will allow you to make the decks parallel to the main centerline.
If you intend to increase dis­placement by moving to larger cyl­inder bores, be aware that factory aluminum blocks have bore liners that are installed during the cast­ing process. The liners are relatively thin, allowing an overbore of only about .005 inch to a maximum of about .010 inch. If you intend to go .010 inch oversize, a sonic wall-thickness gauge should be used to measure wall thickness before any oversizing is performed. Factory iron blocks can be oversized more, again assuming that you’ll have at least about .200-inch wall thickness once the bore has been machined. Factory iron blocks can routinely be larger than the specs given by .030 inch, with some capable of handling as much as a .060 inch oversize, again, only if cylinder wall thickness is not compromised. Not all factory blocks are identical due to core shift during the casting process, so each cylinder should be first checked for wall thickness.

Aftermarket blocks tend to pro­vide thicker cylinder walls, poten­tially allowing larger oversizing, but always check with the block manu­facturer for the bore diameter lim­itations. Always refer to the piston skirt diameter of the pistons that will be installed to determine the required piston-to-wall clearance. Piston-to-wall clearance can vary depending on the piston material and the intended use (street, street/ strip, race, forced induction, etc.). Never finish cylinder bores unless you have the intended pistons in hand so that pistons can be mea­sured for skirt diameter.
Lifter bores should also be checked both for diameter and for angle. Depending on the lifters being used, desired clearance can vary, with advised clearances of some aftermarket lifters in the .0015-inch area. Always measure lifter diameter and verify that lifter bores are sized appropriately for the lifters that will be installed. Although not extremely common, due to potential core shift in factory blocks, lifter bore angles may be not perfectly perpendicu­lar to the camshaft. Using specialty aftermarket accurizing fixtures or with the use of CNC machining, lifter bores can easily be corrected if needed. If the process of correcting results in oversizing, bronze bushing can then be installed and machined to size.

While GM LS blocks feature main caps secured with two primary bolts and two side bolts, some aftermarket blocks eliminate the side pinch bolts and fea­ture a four-bolt main cap design.

This view of a six-bolt deck clearly shows the extra head bolt holes above and below each cylinder, inline with the cylinder centerline.

Aside from these modifications, clearance checking when using a longer-stroke crankshaft is always required, with clearances measured between crank counterweights and the block pan rails, connecting rod big end to pan rails and cylinder bottoms, and rod big ends to cam­shaft lobes. Naturally, this is done during initial test assembly before any machine work is done.

Disabling Performance- Robbing Displacement on Demand

For high-performance LS Gen IV engines, the displacement on demand (DOD), also called active fuel management (AFM), must be disabled because it will restrict per­formance. Many of the LS Gen IVs use this system, except for the LS7 block. It disables four cylinders during certain driving conditions, such as easy cruising with low engine load. The only purpose of DOD/AFM is to increase fuel economy, a factor that isn’t high on the priority list for most performance-minded owners.

When DOD is signaled, cylinders 1-4-6-7 are shut down by effectively disabling their valves and by cutting off the spark to their ignition coils. This happens when solenoids on the underside of the valley cover allow high-pressure oil to be delivered to a groove in the special two-part DOD lifter that causes a pin to collapse a spring-loaded pin in the lifter. The two parts of the DOD lifter are then free to move relative to one another. The cam lobe keeps pushing on the lifter follower, but the inner part of the lifter pushes against a coil spring at the top of the lifter to prevent the force from being transferred to the pushrod, so that the rocker arm does not push on the valve. When the DOD system turns on, the V-8 engine effectively becomes a 4-cylinder engine, saving fuel.

When more power is required, the lifters are activated. The opera­tion is controlled by the engine con­trol unit (ECU) and four solenoids located in the lifter valley. The sole­noids provide a pressurized oil sig­nal to the roller lifters. The system is tuned to a specific camshaft profile, with different lobe profiles between AFM and non-AFM cylinders and different valve lash requirements. DOD/AFM lifters were utilized in various 2006–2015 Gen IV LS engines. Examples include 5.3L engines in various vehicle applica­tions, 6.2L L94 engines in Cadillac Escalades, 6.0L L76 engines in 2007– 2009 Chevy Avalanches, 6.2L L99 engines in 2012–2015 Camaros, and 6.0L L77 engines in Chevy Caprice models.

If a more aggressive cam is installed, the DOD/AFM system must be disabled, requiring not only the cam change but also installa­tion of different lifters and lifter guides. In addition, the ECU must be recalibrated. Any competent GM dealer’s service department can

The oil passages in the DOD/AFM towers are open on this block, and at this stage, it’s ready for tapping and plugging.

The oiling towers of this LS7 block are blank and not drilled open. Since some engine applications feature DOD/AFM and some don’t, a common casting was made, with towers drilled for oil passages when factory produc­tion called for the DOD/AFM feature.

This factory LS7 block has the four-bolt-per-cylinder-head bolt layout, the sia­mesed cylinder bores, and the main cap side bolt holes. The siamesed bore provides additional strength to the block and the four-bolt head provides extra clamping force for high-horsepower output.

The Lingenfelter rivet tool allows easy plugging of DOD/AFM oil ports in the valley stands. (Photo Courtesy Lingenfelter Performance)

After installing a rivet to the tool, insert the rivet into the oil port with the tool arms spread apart. (Photo Courtesy Lingenfelter Performance)

With the rivet tool held against the stand, begin to squeeze the tool arms to begin rivet expansion. (Photo Cour­tesy Lingenfelter Performance)

Continue squeezing the tool arms until the rivet fully expands and the mandrel snaps free. (Photo Courtesy Lingenfelter Performance)

No additional sealant is required. The aluminum plugs seal the ports and will not loosen. If you wish to eliminate the DOD/AFM system, these holes must be plugged to avoid a reduction of oil pres­sure. If an aggressive camshaft is being installed, the DOD/AFM system must be disabled. (Photo Courtesy Lingenfelter Performance)

reprogram (reflash) the ECU to keep the computer from detecting the on-demand lifter deactivation. If this reflash isn’t done, the driver will see a check engine light illuminated on the instrument cluster.

Note that the LS7 block fea­tures the same oil pedestals in the lifter valley, but they are not drilled open; there’s no need to make modifications because this block is not equipped for DOD lifter deactivation.

Many builders elect to elimi­nate DOD/AFM because it is sim­ply not needed when the goal is to gain full advantage of the engine’s performance at all times. Eliminat­ing DOD/AFM requires plugging all oil delivery ports in the standoffs located in the block’s upper valley. If these ports are left open, internal oil leaks will result in low oil pres­sure. The oil ports in the valley can be plugged by drilling and tapping each port and installing 1/8-inch NPT plugs, but this should be done only on a bare block that will be properly washed and rinsed after machining operations.

Rivet Plugs

Lingenfelter Performance offers a slick alternative that can be handled even on an assembled block. This essentially involves installing an alu­minum rivet plug in each port with the use of a manual rivet tool. This requires no machining, so the con­cern about leaving metal particles and shavings inside the oil passages is eliminated.
To install a rivet, put the rivet into the rivet tool. With the tool’s arms spread apart, insert the rivet into the oil port. While holding the tool against the port surface, squeeze the tool’s arms together to expand the rivet. Once the rivet fully expands, the rivet mandrel will snap off and remain in the tool. The aluminum rivet plug will seal the port with no additional sealing required. Lingen­felter’s installation tool is available as PN L950105305, which includes a set of rivets. Additional eight-rivet sets are also available as PN L960225305. This is a slick, easy, and no-mess method of sealing the oil ports on either a bare or assembled block.

DOD Delete Kits

Eliminating the DOD system isn’t complicated. This involves closing off the oil passages in the DOD towers, replacing the four cyl­inders’ intake and exhaust lifters with “regular” LS lifters, replacing the DOD-location plastic lifter guides with standard non-DOD lifter guides, replacing the camshaft with a non-DOD cam, and eliminating the solenoids by replacing the lifter valley cover. You can source all the items individually, or you can buy a DOD-elimination kit from Gen­eral Motors or various aftermarket sources.

A GM Performance Parts DOD delete kit is available under GM PN 12570471. This kit includes a three-bolt 4X cam sprocket, ARP cam sprocket bolts, LS2 chain damper, LS7 lifter set, LS3/L92 head gaskets, OEM head bolts, exhaust manifold gaskets, LS2 valley plate, a set of four standard plastic lifter guides, PCV dirty air hose, PCV valve cover plug, and a new GM balancer bolt. Install­ing the kit also requires the use of an aftermarket camshaft that was not designed for use with DOD/AFM along with ECM reprogramming.

One example is Summit Racing’s PN CMB-09-0026, which includes a set of lifters, lifter guides, val­ley cover, and head bolts. Another DOD/AFM delete kit is Tick Perfor­mance’s PN 5065TP. This includes an LS3 valley cover, LS2/LS3/LS7/ LS9/L92 lifter trays, a full set of LS7 lifters, head gaskets, head bolts, LS2/ LS3/LS7/L92 timing chain damper, LS2 PCV hose, PCV cap, timing cover gasket, water pump gaskets, timing cover seal, and a GM crank balancer bolt.

Main Caps

All GM factory LS blocks feature a six-bolt main cap design, with four pri­mary 10-mm x 2.0 vertical bolts and two 8-mm x 1.25 “pinch” or “cross” bolts that pass through the lower block sides into the caps. All factory LS blocks also feature powdered-metal main caps except the LS7 and LS9 blocks, which use forged-steel main caps. Powdered metal caps have proven to be satisfactory for builds up to the range of about 500 hp. Beyond that horsepower range in a naturally aspirated engine, and especially if higher cylinder pressures are planned due to nitrous injection and/or forced induction, aftermarket forged-steel main caps along with stronger main bolts or studs, such as those offered by ARP and other sources, are highly recommended.

Aftermarket Blocks

If you want to up the ante for increased block strength and/ or more displacement, several high-performance blocks are avail­able in the aftermarket for radical street or all-out racing applications. Available in cast iron, cast aluminum, and even billet aluminum, these blocks are designed as an improve­ment of the factory LS design to accommodate higher-horsepower applications and better withstand the abuse of increased cylinder pressure at higher engine RPM, increased compression, and/or forced induction. Several designs also provide enhanced priority main oiling circuits and improved cooling jacket designs, along with available beefy billet-steel main caps. These aftermarket blocks offer increased durability for higher-demand applications.

Dart LS Next Block

Dart offers an array of LS-based blocks designed to provide superior power, reliability, and durability.

While most factory production LS blocks feature powdered metal main caps (except the LS7, which features steel-billet caps) that use 8-mm side “pinch” bolts, some aftermarket blocks utilize steel-billet four-bolt main caps with outer splayed bolts, such as this example of a Dart LS Next block.

You can see the machined ends on the LS7 billet-steel main caps that accept the 8-mm side bolts. Doweled-in forged-steel main bearing caps provide excellent support for the crankshaft.

An aftermarket LS block alternative is Dart’s LS Next block, with thicker decks and elimination of the Y-block extended pan rails for crank windage improvements. Full-skirted blocks are also available.

Several performance aftermarket blocks are available, allowing a stron­ger build for higher cylinder pressure and extended RPM applications. Shown here is Dart’s LS Next block, which features thicker decks, priority main oiling, thicker cylinder walls, and a more-dense high-nickel casting. Similar to design features found in GM LSX race blocks, the decks offer six-bolt-per-cylinder-head fastener locations.

Dart’s LS Next block also features four-bolt steel-billet registered main caps, eliminating the need for main cap side bolts.

The inboard “extra” head fastener locations on the Dart block are smooth-bored, requiring studs that secure to the head deck. The studs pass through the open holes and are secured with shouldered washers and nuts from the valley side.

Some aftermarket LS blocks fea­ture the six-bolt head-bolt design, with extra upper and lower head bolt holes added at each cylinder location, as shown on this Dart LS Next block. Head studs provide added strength.

Because the Dart LS Next block’s pan rails have been shortened by 2 inches to improve windage, accommoda­tion is required to mount the oil pan. Choices include a custom pan from Canton or Stefs (these are designed with taller sides) or a pair of spacer rails that mount to the block, effec­tively regaining the needed mounting surface for the oil pan.

With the Moroso 2-inch rail spacers in place, an LS-style oil pan may be mounted. Here a Moroso pan is installed.

Dart’s billet LS block is entirely machined from a chunk of high-grade alumi­num alloy to finished state on CNC, offering an increase in strength as well as weight reduction. The OEM cast-aluminum bare block weight is about 110 pounds for LS1/LS6/LS3/L92. The weight of Dart’s billet block is about 125 pounds, depending on deck height and bore size. The slight increase in weight compared to the OEM casting is inconsequential, given the billet block’s vastly increased strength. As a reference, the OEM cast-iron LQ9 6.0L block weighs in at about 170 pounds. Shown here is a billet block ready for final cylinder honing to accommodate the builder’s specific piston diameter. (Photo Courtesy Dart Machinery)

Dart’s LS Next MID block features a modular integrated deck design that offers increased cylinder integrity and strength. According to Dart, the distortion is removed from the deck and the sleeves are anchored in com­pression in the lower block area for enhanced strength. (Photo Courtesy Dart Machinery)

The recently introduced World Prod­ucts Motown II LS iron block incor­porates aftermarket-influenced and enhanced small-block Chevy archi­tecture. It features a 9.240-inch LS deck height with a .134-inch raised cam bore, combining the strength of a performance-upgraded tried and true small-block Chevy with the vastly supe­rior breathing of LS cylinder heads.

The most notable design features of the Motown II LS block are the LS cylinder head bolt locations, deck height, and cooling passages.

The lifter bore locations are spe­cific to the LS lay­out. Bushed lifter bores are stan­dard and must be final-machined to accommodate the lifters of choice. Blocks can be ordered to accom­modate either .847- or .904-inch lifters.

The mandatory aluminum valley cover base not only provides a cover for the lifter valley but the angled sides also extend the block’s deck surface to complete the footprint for the LS cylinder heads and feature 5/16-18 threaded holes to accept the heads’ inboard pinch bolts. The base also features a distributor mounting flange to accommodate con­ventional small-block Chevy distributor mounting. Since the valley cover base completes the deck surface area for the heads, this base must be mounted to the block during final deck surfacing.

In addition to Dart’s offerings of billet-aluminum and cast LS blocks, the company has also introduced its LS Next block, a further evolution of the LS format.

Dart’s latest block is vastly improved compared to the factory block. It is offered in iron or alu­minum; the LS Next block features radical enhancements that include elimination of the factory Y-block skirt for reduced windage and allow­ing for thicker, stronger full-main web architecture. In addition, the design incorporates extended cyl­inders that are .375 inch longer at the bottom for better piston skirt support at BDC; low-restriction priority main oiling system; and four-bolt main caps with 7/16-inch bolts. Deck heights are offered in both stock 9.240-inch and optional 9.450-inch sizes to allow displace­ment increases. Thicker siamesed bores provide for increased over­sizing potential for added displace­ment. Thicker 5/8-inch decks have been added for rigidity. A larger water jacket is installed at the number-1 cylinder, and in the valley is a provision for oil restrictors.

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The LS Next block is designed to easily handle 1,500-plus-hp levels when the engine is pushed hard, as in racing conditions. I’ve seen reports of this block in applications push­ing past 2,500 hp. These blocks are intended for extreme conditions in motorsports applications. Although I have not built an engine approaching the 2,000-hp level, I certainly view this type of block to be most suitable for extreme power levels, far beyond what a factory stock block could handle. Keep in mind that even the highest-grade block can fail because of problems with other component issues and/or incorrect assembly techniques, such as less-than-robust connecting rods, inadequate valve-to-piston clearance, improperly tightened rod bolts, inadequate bear­ing clearances, poor oil delivery, etc. But if you want a strong basis for a high-performance build, aftermar­ket blocks such as the LS Next offer vastly improved strength and dura­bility. Blocks such as these provide a sturdy foundation for extreme power builds. Keep in mind that an engine block unto itself does not make more power; the design and strength incor­porated into the block simply allow you to build more power and to bet­ter withstand extreme abuse.
Note: A special oil pan is required because of the elimination of the Y-block skirts. Both Canton and Stefs currently offer an appropriate pan, and Moroso carries a dedicated oil pan kit. The Canton and Stefs pans feature 2-inch-taller rails built into the pan design, while the Moroso kit uses 2-inch-thick spacers. This is required to compensate for the 2 inches that were removed from the block’s pan rails.

Dart LS Billet Block

One of the many block designs offered by Dart is its billet LS block. The block is machined from a blank chunk of high-grade, aerospace-quality aluminum alloy, offering “virtually unlimited” choices of specifications, including bore centerline, bore diameter, deck height, lifter bore sizes, and cam tunnel height placement. Basically, it’s custom machined to your spec block, offered with either steel or aluminum main caps.

Dart LS MID Block
Dart’s LS Next MID block features a modular integrated deck as well as a wet cylinder design to virtually eliminate cylinder distortion from block flexing and harmonics. Cylin­der sleeves are seated and anchored in compression in the lower block area where the maximum alumi­num mass is concentrated, offering increased cylinder integrity and strength compared to dry sleeves. Compatible with all currently avail­able LS head designs, the Next MID is available in 9.240- and 9.750-inch decks heights and 4.125- to 4.220-inch bore sizes. It requires the use of MLS head gaskets.

World Products Motown II LS Block
This block represents a distinct departure from a typical LS design because the block is essentially a Gen I small-block Chevy design. However, it accepts LS cylinder heads, crankshaft, rods, oil pan, and distributor, but the distributor can be eliminated if you prefer to use a controller and LS coil packs. It also accepts a water pump, crank balancer, oil pump, and other com­ponents. The block’s deck height is 9.420 inches with an LS head bolt pattern to allow the use of LS-style heads. The LS-style components include cylinder heads, LS-style pistons, rockers, lifters, and intake manifold.

The block requires the use of a special camshaft that is essentially a small-block Chevy cam (with dis­tributor drive gear) that features LS cam lobe spacing. The camshaft, which must be custom ordered to meet lift, duration, and LSA requirements, is currently offered by Comp Cams and Erson. Don’t be alarmed at the “custom order” aspect: normal delivery time is only about a week or so. This block design is intended to offer the best of both worlds, combining the easy access and flexibility to accept more affordable tried and true Chevy small-block components with the vastly improved performance of the LS cylinder head designs. A spe­cial aluminum valley cover base is available with or without a distrib­utor mounting hole. A separate flat aluminum valley cover plate seals the lifter valley.

One “unusual” aspect of the block is the use of two external cool­ant hoses that run from each side of the block to a high-mounted water housing. Each side of the block fea­tures a threaded water jacket hole that accepts a 1¼-inch NPT male thread fitting that accepts a –12 AN 90-degree hose end. The –12 AN hoses then connect to the coolant fill reservoir that is mounted to the front of the block. The housing fea­tures a hose neck for upper radiator connection.
In fact, I recently built a 427-ci engine using one of these blocks. It featured a 4.125-inch bore and 4.000-inch stroke. Components included a Scat 4.000-inch stroker crank, Scat 6.125-inch rods, JE pis­tons at 1.115-inch compression height, .624-inch-lift Erson hydrau­lic roller cam, Trick Flow LS CNC heads, Holley single-plane intake manifold and 850-cfm carb, MSD distributor, Fluidampr balancer, Melling oil pump, Moroso pickup and pan, Cloyes timing set, Comp aluminum roller rockers, Trend 7.500-inch pushrods, and ARP main and head stud kits. On the dyno, it easily pulled 641 hp and 555 ft-lbs of torque.

One of the cool features of the block is the motor mount bolt hole locations: both small-block Chevy and LS patterns are built in, allow­ing an easy swap into any vehicle that was originally intended for a Gen I Chevy or an LS engine.

RHS Race Block
RHS’s LS Race Block, cast from A357T aluminum alloy and CNC-machined, is intended for all-out race applications. Press-in spun-cast extra-long cylinder bore liners can be finished to 4.125- to 4.165-inch bore diameters. Available in standard LS 9.240- or tall 9.750-inch deck height, the block is designed to accept up to a 4.600-inch stroke and can accom­modate up to a 60-mm roller bearing cam. The cam centerline is raised .388 inch to allow for longer stroke. Based on LS7 design, the decks feature a six-bolt-per-cylinder layout with a full water jacket around each cylin­der. The block will accept either LS or early generation motor mounts (bell­housing mounts will also accept early or late bellhousings).

BMP LS Block
The Bill Mitchell Products (BMP) LS7X race block is an aluminum four-bolt steel main cap block that features an OEM main bore (to accept any LS crank). Deck height choices include standard LS 9.240 inches or 9.800 inches. Cylinder bores are available in 4.000 inches and can accept up to 4.185 inches. Other fea­tures include priority main oiling, LS and Gen I motor mount locations, billet-steel main caps, cam bores that can be machined to 60 mm, and six-bolt-per-cylinder-head bolt loca­tions. The block will readily accept crank strokes up to 4.250 inches.

As is the case with most aftermarket performance blocks, this block is already notched for rod clearance, in this example for a 4.000-inch stroker crank. Additional notch clear­ancing may be needed for longer strokes.

When order­ing a block, options include a choice of either modular or steel-billet main caps. The steel-billet 3, 4, and 5 caps feature splayed outer bolt locations.

As a convenience feature, both small-block Chevy and LS motor mount bolt holes are provided, making it easy to install this block in an early vehicle that originally had a small-block Chevy engine or a later vehicle that was equipped with an LS engine; no custom motor mounts are needed.

RHS offers its LS Race Block, a cast-aluminum block that is fully CNC-machined, intended for racing applications. Consider­ing optional raised-deck versions and the ability to accommodate as much as a 4.600-inch stroke and 4.165-inch cylinder bores, these blocks are capable of 500-plus ci of displacement and are designed to withstand an estimated output of 2,000 hp. (Photo Courtesy Racing Head Service)

The BMP LS block is cast aluminum and will accom­modate up to a 4.185-inch bore and 4.250-inch stroke. The block has many unique features that support max-performance builds. The main caps are 1045 steel alloy rather than 1020. The block has priority oiling that lubricates the crankshaft mains first and the top end sec­ond. (Photo Courtesy BMP)

Written by Mike Mavrigian and republished with permission of CarTech Inc

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Nitrous oxide offers a number of benefits, including the ability to adjust the available power level. Much like cranking up the boost pressure on a turbo, jet changes on a nitrous system allow you to liter­ally dial in the extra power. How­ever, there is a limit to the amount of nitrous that can be added, something usually dictated by the strength of the internal components and the original power output of the engine.

In addition to the adjustable power, street racers like nitrous because it can be easily hidden. Of course, it doesn’t take a genius to figure out that a stock 2010 Camaro was sporting something more than the stock when it knocks out consis­tent 11s at the track. Further improv­ing upon the adjustable power and concealment is the cost. Compared on the basis of available power gains, nitrous offers far and away the best bang for the performance buck.

As you know, nitrous oxide is not a fuel, but rather it’s an oxidizer. Despite the automotive infernos depicted in movies such as The Fast and the Furious, nitrous oxide does not burn nor is it likely to inciner­ate a car. You could literally open the bottle of nitrous and touch a match to the spray and the only thing that would happen is that the match would go out. No thunder­ous explosions, no massive fire balls, just an anticlimactic wisp of smoke as the flame is extinguished by the high-pressure, ice-cold stream of nitrous oxide.
If nitrous oxide doesn’t burn, then how does it increase the power output of the engine? The answer is simple: Nitrous oxide adds power by releasing free oxygen molecules contained in the compound. Because oxygen molecules are a key ingredi­ent in power production (the more oxygen present, the greater the power potential), the release of these oxygen molecules adds to the power potential of the engine. More nitrous equals more free oxygen molecules, which in turn equals more power.

Nothing wakes up an LS3 or LS7 applica­tion like a small shot of nitrous. Combine the right amount of nitrous and fuel through a single (or multiple) fogger noz­zle(s) and you have instant horsepower.

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There is, however, a limit to the amount of nitrous and the number of attending free oxygen molecules that can be added to any combina­tion. While most stock engines, even those equipped with cast or hypereu­tectic pistons, withstand an increase of 40 to 50 percent (depending on the original power output and displace­ment), adding more power brings the strength of the internal components into play.

Building a high-horsepower nitrous engine is not much different than building a high-horsepower tur­bocharged or supercharged engine. Short-blocks typically include forged rods, cranks, and pistons, with MLS head gaskets, head studs, and pos­sibly O-ringing the block. Nitrous and forced induction engines do, however, differ in their cam timing and cylinder head porting. Nitrous engines prefer big port volumes and a lot of exhaust flow because the nitrous adds all the necessary intake oxygen molecules. All those extra oxygen molecules must now be allowed to escape, thus the need for greater exhaust port flow and wilder exhaust cam timing.

Adding power through nitrous is different than adding the same amount of power through forced induction. Sure, both add an easy 75, 100, or even 150 hp (or more) to an average LS engine, but how they add the power differs. Both forced induc­tion and nitrous increase the amount of oxygen molecules available to produce power. Forced induction does so by increasing the mass flow of air. Pressurizing the air increases the mass flow, thus force-feeding the engine more air than it could ingest on its own or otherwise in NA form.

The unfortunate side effect of the pressurization of air (boost) is that the pressure causes heat. Tur­bochargers and superchargers heat the inlet air, something not desir­able from either a power (less oxygen molecules per volume) or a detona­tion threshold standpoint. The hot­ter the air, the easier it is to ignite. In some cases, the heated inlet air can self-ignite before the spark plug initi­ates the burn. The result is an expan­sion of the air/fuel mixture while the piston is still on its way to TDC. As a result, the expanding gases resist the upward moving piston. The result of this struggle is sometimes not very pretty. The same thing can happen with excessive ignition advance.

Nitrous, on the other hand, does not resort to pressurizing the inlet air, but rather the extra oxygen mol­ecules are carried in the pressurized compound. Once delivered to the inlet tract from a pressurized bottle, the liquid nitrous quickly turns into a gas. This liquid-to-gas vaporization requires an input of energy; in this case the energy is heat. The vapor­ization of the liquid nitrous absorbs heat from the surrounding inlet air, desirable in any performance appli­cation (especially a turbo or super­charged engine).

Although you associate heat with boiling (for example, water turning from a liquid to a gas), the vaporized nitrous does not produce heat (at least not to the inlet air). Although vapor­ized, the temperature of the nitrous oxide is still at or near minus 129 degrees F (the boiling point of nitrous oxide). Mixing the inlet air with a gas that is even that cold still provides a dramatic cooling effect. This double cooling reduces the chance of deto­nation and increases the density of the inlet air. Denser air equals more oxygen molecules, which in turn (potentially) creates more power.

Nitrous kits can be pretty elaborate but most feature the components illustrated in this NOS kit. The components include a bottle, sole­noids, fogger or plate, jetting and arming, and activation switches.

Nitrous oxide (such as in this Zex kit) can also be used on carbureted LS applications with the Perimeter Plate system. This system was designed to evenly distribute the fuel and nitrous to all cylinders to maximize (safe) power.

Test 1: Modified LS3: NA vs Nitrous Using 100- and 150-hp Shots

The great thing about nitrous oxide is that it can be added to any engine, but big doses of nitrous are best used on modified engines designed to take the abuse. After all, nitrous kits can easily increase the power output of an NA engine by 100 hp or more.

This test was run on a modified LS3. Starting with a GM LS3 crate engine from Gandrud Chevrolet, the short-block was augmented with a set of CP forged, flat-top pistons and 6.125-inch connecting rods. The piston and rod upgrade were combined with the stock crank (more than strong enough for this level of nitrous). I retained the stock LS3 heads, but they were treated to a valve spring upgrade from BTR. Comp Cams supplied a 459 cam for this test that offered a.617/.624-inch lift split, 231/239-degree duration split, and 113-degree LSA. The stock heads were retained using Fel-Pro MLS head gaskets and ARP head studs. This test relied on the stock LS3 intake, but I swapped on a manual 90-mm throttle body to replace the factory drive-by-wire unit. Run with long-tube headers, a Meziere electric water pump, and FAST XFI management system, the modified LS3 produced 552 hp, and 520 ft-lbs of torque.
To illustrate the power gains offered by nitrous oxide, I selected one of the affordable Sniper Kits from NOS. Because one of the benefits of nitrous is the ability to easily increase power with a simple jet change, I decided to run two different power levels on this engine. The Sniped Universal EFI kit featured a 10-pound bottle, two solenoids, and a single fogger nozzle designed to inject the nitrous and fuel together. Because nitrous oxide is an oxidizer, extra fuel is a critical component to add to the extra oxygen molecules supplied by the compound. Using the supplied jetting, I set up the system to provide an extra 100 hp. Activating the nitrous at 4,300 rpm resulted in a jump in power to 687 hp and 684 ft-lbs of torque. The Sniper system provided a nice, smooth power curve. After the success of the 100-hp shot, I stepped up to 150-hp jetting and was immediately rewarded with 732 hp and 730 ft-lbs of torque. I made sure to heat the bottle properly to ensure adequate bottle pressure prior to testing.

Because the stock valve springs did not accept the available cam lift, I replaced them with a dual-valve spring upgrade from BTR.

In addition to forged rods and pistons, the LS3 also received a Comp 459 cam upgrade.

The Sniper universal wet EFI system offered plenty of bang for the buck. Applied to this modified LS3, the nitrous system increased the power output from 551 to 687 hp using the 100-hp jetting. This increased to 732 hp with the 150-hp jetting. Thanks to the forged internals from CP and Carillo, I felt confident adding this much power to the LS3.

The torque curves illustrate how easy it was to increase power on the nitrous-injected LS3. Simple by chang- ing jets on the Sniper system, I was able to increase torque production first from 520 ft-lbs to 684 ft-lbs, then up to 730 ft-lbs with the 150-hp jetting. Note the 300-rpm earlier activation (4,300 versus 4,600) on the 100-hp shot.

Test 2: 408 Hybrid Stroker: NA vs Zex Wet EFI Nitrous Using a 100-hp Shot

Aluminum LS3 engines are expensive and more difficult to come by than iron 6.0 truck blocks, and as a result, building your own 6.0 LS3 hybrid has become common practice. This works especially well if you bore and stroke the 6.0 to 408 ci as with this test engine.

The 6.0 iron block was fi rst bored .030 over then treated to a stroker assembly that included a Scat forged steel crank and 6.125-inch rods combined with JE forged (asymmetrical) pistons. Finishing the stroker was a Comp cam (PN 277LrHR13) that offered a .614/621-inch lift split, 227/235-degree duration split, and 113-degree LSA. Making this a hybrid was the fact that I topped off the .030-over iron block with a set of as-cast LS3 heads treated to a Comp beehive valve spring (PN 26918) upgrade. The engine was run with a stock LS3 intake, FAST injectors, and a Holley HP management system. As always, I replaced the drive-by-wire throttle body with a 90-mm manual version. Equipped as such, the NA LS3 hybrid produced 577 hp and 526 ft-lbs of torque.

After running the NA hybrid stroker, I installed the Zex Wet EFI nitrous kit. The cool thing about the Zex kit is that not only was it adjustable with different jet- ting, but the single fogger nozzle could be applied to just about any fuel-injected application. The kit included the purple 10-pound bottle, a digital controller, and a single fogger nozzle designed to combine the nitrous and fuel before injecting it into the engine.

After filling the bottle at Westech Performance, I hooked up the system, went through the WOT learn procedure for the throttle position sensor (TPS), then purged the system. With plenty of bottle pressure, I activated the Zex nitrous at 4,500 rpm, and the power jumped immediately. It soon settled in with gains that exceeded 100 hp. Credit the extra power offered by the kit to tuning and bottle pressure above 1,000 psi. Increased bottle pressure works like a larger nitrous jet, and this Zex kit worked amazingly well on this hybrid stroker.

The test engine started as a 6.0, but the iron block was upgraded with a 4.0-inch SCAT stroker crank and K1 6.125-inch rods.

JE supplied the necessary forged flat-top pistons for the LS3-headed 6.0 stroker.

Nothing adds instant power like a good nitrous system. The Zex Wet EFI kit offered impressive power gain, upping the power output of the 408 hybrid stroker from 577 hp to 702 hp using 100-hp jetting. I did take the necessary steps to ensure proper nitrous pressure and delivery by preheating the bottle.

It is not unusual to see a massive torque gain on the initial activation of a nitrous system. The Zex kit added more than 200 ft-lbs to the stroker engine at 4,900 rpm but settled in to a more real- istic torque gain thereafter. Remember, the lower you activate the nitrous, the more torque you gain, but care must be taken not to become too greedy.

Test 3: Mild LS3: NA vs Nitrous Works Using a 100-hp Shot

I ran this test to illustrate that it is possible to not only add nitrous to any LS3 or LS7 combination (even a stock one), but do so safely. Forget the horror stories and explosions shown on TV, movies, or YouTube, nitrous is not even flammable, nor does it hurt stock pistons or rods if tuned properly. Nitrous is simply an oxidizer that adds extra oxygen molecules. Extra oxygen means extra power, but the oxygen must have additional fuel to support the burn. Combine the two properly and inject into the engine and that’s when the magic starts to happen.

To illustrate how well nitrous companies have perfected their systems, I ran nitrous on an LS3 equipped with stock internals, meaning powdered-metal rods and cast pistons. The only upgrades made to the LS3 were a BTR cam and valve springs. Run with headers, a Meziere electric water pump, and Holley HP management system, the cam-only LS3 produced 544 hp and 514 ft-lbs of torque. (See Chapter 3 for some serious cam-only information from BTR.).

As much as I love how well an LS3 responds to more aggressive cam timing, it responds even better to nitrous oxide. This includes an old, out-of-date system no longer available. Rummaging through the cabinets at Westech Performance, I ran across an old Nitrous Works kit from Barry Grant. No longer available, the system was complete and ready to run. The Nitrous Works system included the usual array of solenoids, lines, and a single fogger nozzle, along with a 10-pound bottle, activation switch, and various hoses and fittings.

To test the system, I installed jetting to provide a 100-hp increase to the cam-only LS3. Despite not being available for some time, all the components worked well and the 100-hp jetting increased the power output of the LS3 from 544 to 660 hp. The torque gains were equally impressive; the nitrous increased torque production from 514 to 655 ft-lbs. Even on a near-stock engine, nitrous oxide works wonders.

The power output of the GM LS3 crate engine was increased by replacing the factory cam with a higher lift cam from BTR.

The cam swap necessitated replacement of the stock LS3 valve springs. BTR supplied a set of double springs to accommodate the higher-lift and increased engine speed of the new cam.

Starting with a GM LS3 crate engine from Gandrud Chevrolet, I installed a mild BTR cam (and springs), then an old Barry Grant Nitrous system that I had laying around. Running jetting to supply an extra 100 hp, the single fog- ger system increased the power output of the mild LS3 from 554 hp to 660 hp. Nitrous offered nice, smooth, consistent gains.

Activation of the Nitrous Works nitrous system at 4,500 rpm resulted in impressive torque gains. I made sure to retard the timing by 4 degrees to eliminate any chance of detonation. Nitrous can transform a mild LS3 into a wild one with one push of the button.

Written by Richard Holdener and republished with permission of CarTech Inc

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I have seen power gains eclipsing 70 hp when upgrading cathedral-port heads (on a 408 stroker), but the gains were nearly half that (or less) when replacing factory LS3 heads (on a larger 468 stroker). The reason for this is not that the aftermarket doesn’t know how to produce a good LS3 head, but that the factory LS3 heads already flow enough to support such high power levels. A stock LS3 head flows near 318 cfm. This compares to the very best cathedral-port head (317 or 243) that flows 244 cfm. The difference between an LS3 and the best factory cathedral-port is more than 70 cfm.

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Bolting on the right set of LS3 or LS7 cylinder heads can yield impres­sive power gains.

Factory LS3 and LS7 heads offer exceptional flow and power potential, but CNC-ported, aftermarket heads offer even more.

Using a flow bench is one way to deter­mine the power “potential” of a set of cylinder heads, but the only way to know for sure is to run them on a dyno.

For the ultimate in valve control and RPM potential, a dual-spring upgrade is the way to go on a high-performance LS3 or LS7.

I have exceeded 690 hp using stock LS3 castings on a 468 stroker, and the stock LS7 heads are even more impressive. Run on a 495-inch stroker, the stock LS7 heads produced 773 hp. The impressive head flow offered by the stock heads is both a blessing and a curse. On the plus side, they offer impressive power right out of the box, but just don’t expect huge power gains when upgrading the heads on your LS3 or LS7.

To understand the reason for this, you need to first understand the cor­relation between airflow and power potential. There is, of course, an equation to calculate the “potential” horsepower offered by cylinder heads using the airflow data. This formula is:

HP = .257 x airflow x number of cylinders

Using an LS3 (with 318 cfm) as an example, the formula indicates (.257 x 234 cfm x 8) that the stock heads will support 653 hp (though have made more than the formula suggests). Were you to upgrade the heads on a stock or mild LS3 (making less than 560 hp), the gains offered by the head swap might be minimal because the stock heads already flow more than enough to support the current power level. Test 1 in this chapter illustrates what happens when you add cylinder head flow to a mild combination.

LS3 and LS7 heads offered by the aftermarket are usually purchased based on flow numbers. The prob­lem with purchasing cylinder heads based on airflow is that the airflow numbers represent only a potential power output. As in the example in Test 1, just because you have 800-hp head flow doesn’t mean your com­bination is in a position to take full advantage of the available flow. This is especially the case in LS7 applica­tions, where aftermarket head flow can exceed 400 cfm (or more). It took a 495-inch super stroker (see Chapter 8) to tax the flow limits of the best LS7 heads, and the stock LS7 heads produced 773 hp.

Even the best heads were only up by 25 hp or so, the gains offered by ported LS7 heads would be even less. On a stock LS7, there may be no gain at all. This is especially the case if the maximum flow rate given for the heads you plan to purchase exceed the lift of the cam you plan to run. Big flow at .700, .750, or .800 lift is useless if you plan to use a .600-lift cam. Besides, you should be more concerned with the mid-lift flow numbers because the valve spends much more of its time sweeping through the mid-lift (opening and closing) than it does at peak lift.

The great thing about the LS engine family is the interchange­ability. Cylinder heads from an LS7 physically bolt onto an original LS1, but the small bore size does not allow them to actually run without valve interference. This interchange allows the later LS3 heads to serve as inexpensive upgrades to the ear­lier cathedral-port engines. The most popular upgrade is to replace the stock 317 cathedral-port heads on a 6.0 truck (LQ4 or LQ9) or LS2 (243 castings) with the rectangular-port LS3 heads. The large valves in the LS3 heads require the 4.0-inch bore of the 6.0 (and do not work on smaller 4.8, 5.3, or 5.7 blocks), but the results are impressive.

The LS3 head upgrade also requires the corresponding offset (intake) rockers and intake manifold, but the stock LS3 heads offer an additional 70 cfm per runner. Tested on a 408 stro­ker, the LS3 head upgrade was worth almost 40 hp over the stock 317 truck heads. The smaller cathedral-port 317 heads offered more power up to 4,000 rpm, but the LS3 heads pulled away up to 6,500 rpm.

Test 1: Stock LS3 vs Chevy Performance CNC L92 on a Stock LS3

Several tests in this book were designed to illustrate what happens when you install the right part on the wrong application. Unlike factory cathedral-port applications, LS3 engines were blessed with high-flow cylinder heads. In terms of head flow, there was a substantial step up from the cathedral-port LS6/LS2 heads to the rectangular-port LS3 heads. That is why adding LS3 heads to a 6.0 is such a popular swap.

As you learn in this chapter, factory heads can support nearly 700 hp on the right application, but that doesn’t mean ported heads don’t offer any power. Just don’t expect the huge gains normally seen with cathedral-port head testing; the stock LS3 heads flow nearly 315 cfm. This test shows that, especially on a stock application, cylinder head flow was not the limiting factor in terms of performance. 

This test was run on the LS3 crate engine from Gandrud Chevrolet in near-stock trim. The engine was equipped with a set of long-tube headers, manual FAST throttle body, and Holley HP management system. Everything else on the engine was left stock, including the camshaft, displacement, and compression ratio. This test was run to illustrate what happens when you increase the head flow on an engine that already has enough cylinder head. 

Run with the stock LS3 heads, the stock LS3 produced 493 hp at 5,700 rpm and 484 ft-lbs of torque at 4,800 rpm. I then installed a set of CNC-ported L92 heads from GM Performance (supplied by Gandrud) that flowed nearly 350 cfm (up from 315 cfm). While the additional head flow could support well over 700 hp, run on this stock application, the ported heads improved the power output to only 503 hp and 497 ft-lbs of torque. Does this mean the CNC-ported heads don’t work? Hardly. See the gains offered in Test 3. 

The test engine was an LS3 crate engine supplied by Gandrud Chevrolet. It was run in stock trim with no changes to the cam, compression, or induction system.

For dyno use, I installed a set of long-tube headers, FAST throttle body, and XFI management system. The crate engine produced 493 hp and 484 ft-lbs of torque with the stock heads.

Replacing the stock LS3 heads with a set of CNC-ported L92 from Chevy Performance netted only minor gains on this otherwise stock LS3 crate engine. The CNC-ported heads flowed considerably more than the stocks, but the mild stock engine simply didn’t need any more flow to support the existing power level. Test 3 illustrates the amount of power that the extra airflow can be worth on the right application.

The torque curve tells the same story because the mild LS3 simply couldn’t use the additional airflow. Because the stock LS3 heads support well over 600 hp, they were more than enough for this stock crate engine. The head swap would be worth much more than 16 ft-lbs on the right application.

Test 2: Stock LS3 vs AFR 245 on a 408 Stroker

Since both the AFR 245 cathedral-port and factory LS3 heads used for this test flowed so well, I made sure I had a solid test engine for the comparison. Starting with a 6.0 block, the 408 was assembled using components from Speedmaster and Wiseco. The stroker assembly included a 4.0-inch forged-steel crank combined with 6.125-inch 4340 forged steel connecting rods and 10-cc dished pistons. 

The forged pistons from Wiseco featured valve reliefs to allow for the hydraulic roller (PN 289LRR HR14) cam (.624 lift, a 239/255 duration split, and 114 LSA) from Comp Cams. Designed for a rectangular-port head application (which may not have favored the cathedral-port heads), the cam was combined with a set of standard-travel lifters and hardened pushrods from Comp Cams.

The .030-over 408 stroker short-block also featured a new timing chain and oil pump from Speed Pro, a set of ARP head studs and MLS head gaskets from Fel Pro, and a Moroso oil pan and windage tray.

Comparing the rectangular-port LS3 and the cathedral-port AFR heads also required an intake swap (to match the respective head ports). To keep the test as even as possible, I selected FAST LSXR intakes for both applications. Both were also run with the same 102-mm Big Mouth throttle body. As always, both heads were run with the same air/fuel ratio and timing values.

Equipped with the stock LS3 heads, the 408 produced 581 hp and 543 ft-lbs of torque. After installation of the AFR 245 heads, the peak numbers jumped to 604 hp and 665 ft-lbs of torque. It must be pointed out that the head swap also included a change in static compression ratio because the chamber volume on the two heads differed by 5 cc (64 cc vs 69 cc). This meant that in addition to the increased airflow offered by the AFR heads (349 cfm vs 316 cfm), they also increased the static compression ratio by .5 points. With the exception of a short, 250-rpm range (from 4,100 to 4,250 rpm), the AFR heads improved the power output from 3,000 to 6,700 rpm. Having more peak power is good, but having extra power everywhere is even better.

The 408 stroker test engine started as an iron 6.0 block but was stuffed with a Speedmaster forged crank and rods and Probe Racing dished pistons. Note the ARP head studs and Fel Pro MLS head gaskets.

Equipped with the stock LS3 heads and FAST LSXR LS3 intake, the 408 stroker produced 581 hp and 543 ft-lbs of torque.

Replacing the stock LS3 heads on the 408 stroker with a set of cathedral-port AFR 245 heads netted impressive results. The combination of increased flow and compression increased the power output from 581 to 604 hp, but the head swap increased power through most of the curve.

The cathedral-port AFR heads improved torque production down low by as much as 18 ft-lbs, but the gains were even more significant above 4,500 rpm. With the exception of a 100-rpm spread (from 4,100 to 4,200 rpm), the head swap improved torque production through the tested rev range.CNC ported right from the factory, the stock LS7 heads were no slouch. Run on the 495 stroker, the stock heads produced more than 770 hp and more than 700 ft-lbs of torque.

Test 3: Chevy Performance vs Brodix vs LPE on an LS7 495 Stroker

Even more so than with LS3 head testing, comparing LS7 heads (especially improved versions) requires a serious test engine. Even at 427 ci, the stock 7.0 isn’t enough engine to tax the flow capacity of the stock LS7 heads, to say nothing of aftermarket heads that flow near 400 cfm. To properly test the merits of ported LS7 heads, I built a serious test mule that offered increased displacement, compression, and cam timing. Only then could I show what ported LS7 heads were really capable of.

Starting with an RHS tall-deck block, I bored out the engine to 4.185 inches then added a big stroker crank. Filling the stroker-friendly RHS block were equally stout components from Lunati, Wiseco, and K1. Lunati supplied a massive 4.5-inch billet stroker crank, which was combined with a set of 6.30-inch forged K1 rods and 4.185-inch Wiseco forged, flat-top pistons. The bore and stroke combined to produce a flow-taxing displacement of 495 ci.

The displacement and flat-top pistons combined with the 70-cc combustion chambers to produce a static compression ratio near 13.5:1. Sealing the beast was a set of Cometic MLS head gaskets secured by ARP heads studs. Additional components employed on the RHS stroker included a Moroso pan, pickup, and windage tray; a custom timing chain from Comp Cams designed specifically for the tall-deck block (1 extra link per side); and the largest off-the-shelf hydraulic roller cam available in the Comp Cams catalog. The 309LRR HR15 offered a .660 lift (with 1.8 rockers), 259/275-degree duration split, and 115-degree LSA. Feeding the beast was a Mast Motorsports (high-rise) single-plane intake designed to accept the Holley 1050 Ultra Dominator carb. Run with the stock LS7 heads, the 495 produced 773 hp and 704 ft-lbs of torque. Adding a set of ported LS7 heads from Lingenfelter Performance Engineering increased the power output to 793 hp and 719 ft-lbs of torque, while Brodix LS7 heads produced 799 hp and 714 ft-lbs of torque.

CNC ported right from the factory, the stock LS7 heads were no slouch. Run on the 495 stroker, the stock heads produced more than 770 hp and more than 700 ft-lbs of torque.

Head swaps on the engine dyno were a snap, but it was necessary to prep the test by checking pushrod lengths for the various cylinder heads.

Much like the LS3 head test run on the 468 stroker, this LS7 head test on the larger 495 stroker showed just how well the stock heads work. CNC ported right from the factory, the LS7 heads offered 773 hp on this RHS-block stroker. Installation of the ported heads from Brodix and LPE pushed the peak numbers near 800 hp, with gains as high as 31 hp.

The torque gains offered by the head swap on the 495 stroker came primarily past 4,500 rpm. There were minor gains before that point, but the extra airflow offered by the ported heads from Brodix and LPE made itself known higher in the rev range. The largest torque gain occurred at 5,400 rpm.

Test 4: Effect of Chamber Volume: TEA vs Speedmaster on an LS3

For the first three tests in this chapter, I have concentrated primarily on airflow, but the power offered by a cylinder head swap is a function of other variables. As mentioned in Test 2 on the AFR versus LS3 heads, a change in combustion chamber volume can alter the power output as well. To illustrate this, I selected two pairs of heads that offered similar flow rates but had a significant difference in chamber volume that substantially altered the static compression ratio. 

Before I continue, it is important to know that an increase in static compression ratio (from 9.0:1 to 10.0:1, for instance) will increase the power output of any engine. The general rule is that the power increases 3 to 4 percent for each full point of compression.

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It is also important to note that this rule is a guideline that is most accurate in what I call the normal range of compression ratios (8.0:1 to 13.0:1). Changes in ratios above and/or below this range have less of an effect on power. Given that the change in compression ratio came from increased chamber volume, the change in chamber shape (irrespective of size) might also have an effect on power production, but that requires a much more difficult test to prove.

This test on chamber volume (and static compression) was run on a 416 LS3 stroker. The stroker was built using a Speedmaster crank and rods combined with a set of JE flat-top pistons. Similar to many of the tests, I tried to lower the static compression to safely apply boost to the combination.

The Speedmaster crank, rods, and JE pistons were given a precision balance job and then assembled using Total Seal rings; Sealed Power bearings; and Fel Pro gaskets, oil pump, and timing chain. The stroker also featured a Texas Speed cam (.614/.621 lift split, 231/239 duration split, and 113 LSA) using Comp hydraulic roller lifters.

Run with the (big-chamber) Speedmaster LS3 heads, the stroker produced 576 hp and 551 ft-lbs of torque. After installation of the (smaller-chamber) Chevy Performance heads (with nearly identical flow numbers), the power output improved to 608 hp and 570 ft-lbs of torque. The change in compression ratio of 1.3 points improved the power output by 5.5 percent.

This test was run on an LS3 crate engine upgraded to stroker status and equipped with a Texas Speed cam, long-tube headers, and two different cylinder heads.

Both the Speedmaster and Chevy Performance heads featured full porting to enhance the flow rates.

Changes in airflow typically improve power in relation to engine speed. The gains increase as the need for airflow increases. By comparison, a change in compression ratio improves power everywhere, from top to bottom. The small(er)-chamber Chevy Performance heads improved the power output of the LS3 stroker from 3,500 to more than 6,500 rpm.

Big torque gains are always welcome and that is exactly what increased compression provides. Of course, there is a limit to the gains offered by further increasing compression because the gains start to diminish past 13.0:1. The change in compression offered by the head swap netted more than 25 ft-lbs at 5,600 rpm.

Test 5: Stock LS3 vs TEA vs Speedmaster LS3 on a 468 Stroker

I ran several ported LS3 heads on the 468 stroker engine. The problem is that I couldn’t show all of the results in one test, so I elected to show this one.

As a recap, the 468 stroker used a Darton-sleeved LS6 block with forged internals from Lunati and JE. Aiding in power production was a healthy static compression ratio of 12.0:1. To allow the stroker to maximize power, I installed an off-the-shelf Comp cam (.624 lift, 255/271 duration split, 112 LSA) along with a set of Comp short-travel lifters. Milodon supplied a pan and remote oil filter to work with the modified windage tray (to clear the stroker). ARP and Fel Pro secured each of the three heads tested. Once again, the two ported LS3 heads were compared to a pair of ported versions, in this case from Total Engine Airflow (TEA) and GM Performance.

The first order of business was to run the 468 with the stock heads to establish a baseline. Equipped with stock LS3 heads, the stroker produced 692 hp at 6,500 rpm and 625 ft-lbs of torque at 4,900 rpm. Next up was a set of heads from TEA, which applied its Stage 2 porting to a set of factory castings. The porting improved the power output from 692 hp and 625 ft-lbs of torque to 719 hp and 631 ft-lbs.

The gains offered by the TEA were most prevalent at high RPM, but there were gains through the entire range. The Speedmaster LS3 heads showed similar gains, but offered slightly more peak power. Equipped with the Speedmaster LS3 heads, the 468 produced 730 hp, but peak torque dropped slightly to 629 ft-lbs.

This testing tells me that the stock LS3 heads are plenty powerful and that a number of different aftermarket heads can offer substantial power gains.

The LS6 aluminum block received Darton sleeves to allow me to bore out the block to 4.185 inches. The overbore was combined with a 4.25-inch Lunati stroker crank.

The Total Engine Airflow (TEA) LS3 heads featured full porting and a valvespring upgrade. The Stage 2 porting increased the flow rate from 314 to 365 cfm.

Compared to the stock LS3 heads, the gains offered by the TEA and Speedmaster heads increased with engine speed. The gains were greatest at 7,000 rpm, especially with the heads from Speedmaster. Where the stock heads started falling off in power, the ported heads were just getting started.

The torque gains didn’t really materialize at engine speeds less than 4,400 rpm. This is where the flow rate of the stock heads was more than sufficient to feed the power needs of the 468 stroker. The torque gains increased with engine speed, but the gains were abundant from 4,500 to 7,000 rpm.

Test 6: Chevy Performance vs TS vs SDPC on an LS7 495 Stroker

The testing performed on the LS7 heads paralleled the testing on the LS3 heads in that I ran several different heads during the dyno comparison. After all, why take the time to set everything up multiple times when you have the test engine ready and all you have to do is swap the heads? In truth, there is much more to this type of testing than simple head swaps.

Every head must be first mocked up to measure for proper pushrod length. The last thing you want to do during testing is search around for pushrods when you have an engine on the dyno. Proper preparation allows you to maximize available (and expensive) dyno timing. This test compares the Chevy Performance CNC LS7 heads (basically stock) and two sets from Texas Speed (TS) and Scoggin Dickey Performance Center (SDPC).

Once again, I used the 495-inch stroker with an RHS tall-deck block, Lunati billet crank K1 forged rods, and Wiseco pistons. The 309LRR HR15 featured a .660-inch lift (with 1.8 rockers), 259/275-degree duration split, and 115-degree LSA. The induction system included a Mast Motorsports (high-rise) single-plane intake designed to accept the Holley 1050 Ultra Dominator carb.

First run with the GM Performance CNC LS7 heads, the 495 stroker produced 773 hp at 6,300 rpm and 704 ft-lbs of torque at 4,700 rpm. After installation of the Texas Speed LS7 heads, the power output jumped to 796 hp and 725 ft-lbs of torque. Credit a peak flow rating of 403 cfm offered by the TS heads for the big power gains. The SDPC LS7 heads offered 389 cfm, which allowed them to produce 802 hp, but torque fell slightly (compared to the TS heads) to 717 ft-lbs.

When you are trying to make more displacement, nothing beats a tall-deck, RHS aluminum block. The tall-deck RHS block allowed me to bore and stroke the LS to 495 ci.

The RHS block featured a dedicated cam retaining plate. The 495 featured a healthy (off-the-shelf) Comp hydraulic roller cam.

As I have come to expect from head porting, the power gains increased with engine speed. Equipped with factory (Chevy Performance) LS7 heads, the 495 produced 773 hp. The TS heads pushed the peak power to 796 hp; the SDPC heads produced 802 hp. The TS heads offered slightly more power through the rev range, but fell off on top compared to the SDPC heads.

The ported heads offered impressive torque gains, with the greatest gain coming at 5,400 rpm. The bump in torque production offered by the TS heads coincided with the dip in torque with the Chevy Performance LS7 heads.

Test 7: Stock LS3 vs TFS Gen X 255 on a Modifi ed LS3

One of the critical components of any LS combination is the cylinder heads. As luck (or design) would have it, the LS3 was blessed with plenty of head flow right from the factory, but that doesn’t mean the stock heads can’t be improved on. Case in point, the Trick Flow Gen X 255 LS3 heads. According to Trick Flow, the Gen X heads combined a peak airflow of 380 cfm with an intake port volume that measured just 255 cc. That is where the Gen X 255 heads get their name. The port volume is important because it’s easy to make big flow with big ports. The key to a successful cylinder head is to maximize flow while minimizing port volume. To put the TFS numbers into perspective, the stock LS3 heads checked in with just 315 cfm from 260-cc ports. The TFS heads offered significantly more flow and less port volume, a true indication of a solid design. The Trick Flow heads also offered a spring package that allowed me to run a healthy camshaft; after all, why upgrade heads on an otherwise stock engine? The TFS heads also featured a spring package that offered 150 pounds of seat pressure and 400 pounds of open pressure.

For a test engine, I once again relied on the LS3 crate engine from Gandrud Chevrolet. Prior to the test, the LS3 was upgraded with a hot Crane hydraulic roller cam. The Crane cam offered a .600-inch lift (intake and exhaust), 232/240-degree duration split (at .050), and 113-degree LSA. This cam was nearing the limit of available piston-to-valve clearance offered by the stock flat-top pistons, or more specifically the lack of valve reliefs. With proper valve reliefs, additional power would certainly be available with more aggressive cam timing, especially given the flow rate of the TFS heads.

The LS3 was run with a Holley HP management system and FAST injectors. With stock heads, the modified LS3 combination produced 552 hp at 6,400 rpm and 513 ft-lbs of torque at 5,000 rpm. After installation of the TFS Gen X 255 heads, the power numbers jumped to 571 hp at 6,500 rpm and 525 ft-lbs of torque at 5,200 rpm. As with other tests conducted in this chapter, the greater the power output of the test engine, the greater the gains with a head swap.

The TFS Gen X 255 heads featured amazing flow (more than 380 cfm) and smaller-than-stock port volumes. Also present was a spring package that allowed me to run the heads with ample camshaft to make power.

Bolting the right set of heads on your modified LS3 is a surefire route to improved performance.

The head swap was worth plenty of power, but this mild combination could not take full advantage of what the TFS heads had to offer. The flow rate suggests the head can feed an N A combination near 800 hp, but on the 550-hp LS3, the head swap was worth near 20 extra horsepower.

I liked the fact that the head swap improved torque production through the entire rev range, even if only by a little down low. Gains on the positive side are always better than having to trade low-speed torque for high-RPM power. Because the stock LS3 heads easily support the power level of this mild combo, the gains offered by the head swap were not what they could be. What these heads need is a 468 or 495.

Written by Richard Holdener and republished with permission of CarTech Inc

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There are two ways to add an in-tank pump to a vehicle: buy a tank with a preinstalled EFI pump (either custom or OEM from a different vehicle) or retrofit the tank. Both options can be pricey, but there are ways to keep it on the cheap as well.

An in-tank pump that can supply the 72 psi at 45 gph fuel-pressure requirement is required. The Aeromotive Phan­tom 340 in-tank retrofit pump has the capabilities to support the LT fuel system and is quite easy to install.
Another option is to use a factory GM fuel-pump module from one of the LT-powered vehi­cles from 2014-and-up that were used in 1/2-ton trucks, Corvettes, and Camaros. The Camaro fuel module is fairly tall, so it does not fit in most car tanks, but the 2014-and-up GM truck fuel mod­ules fit quite well. Installing one of these pumps requires some fab­rication on the fuel tank. The nice thing is that if you use a factory module, the wiring for the pump is basic plug and play.

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New tanks can cost $600 to $1,000. Companies such as Rock Valley Antique Auto Parts build custom stainless steel gas tanks for street rods, hot rods, muscle cars, and trucks. If your car is not on the list, Rock Valley Antique Auto can build a custom tank. These new tanks are very slick, well built, and easy to install, but they come with a high price tag.

 For the 1987 Camaro, we went with option C, which is to install a new pump in place of the origi­nal in-tank pump. If the vehicle had EFI from the factory, such as almost any 1987-and-newer GM vehicles (and a few older models), then it already has a fuel pump in the tank. This upgrade begins by knocking out the retainer ring for the pump assembly.

We went with a Deatsch­Werks DW300 pump kit. This pump can flow the required 75 gph at 45 psi and is capable of using a PWM signal. It is also the same size as the original in-tank pump.

The new pump is shown next to the old. There are a few things that we won’t be using, including the wiring, connectors, and the return line.

First, we removed the old pump and disconnected the wires. The black connecter is also removed.

On the underside of the pump assem­bly is a little vapor line. We removed the cover and the keeper. This will be the wire run.

Up top, the line that went to the vapor filter was cut off. There is still a vapor line attached, but we needed one of these for the port.

This connection must be soldered, do not crimp this. This is a PWM signal wire, and it must be a proper connection.

The solder joints were covered with shrink tubing and then sealed with fuel-resistant silicone for an extra layer of protection.

We routed the pump wires out of the top of the assembly and coated the entire area with some more fuel-resistant silicone.

The pump comes with a plug pigtail. We need to lengthen this and seal it from the gas.

Don’t forget to put the filter sock onto the new pump. We set the pump in the stock location, so there is no concern about the filter not reaching the bottom of the tank.

We mounted the new pump to the assembly with a section of fuel line and a worm clamp. The pump will be secured with a couple of hose clamps to the no-longer-used return line, which is also the support stem.

The unused lines get capped with silicone caps.

Each Rock Valley EFI fuel tank features a dropped sump in the top of the tank. This allows for adequate floor clearance. Each EFI tank comes with a new high-volume, high-pressure fuel pump to feed the engine. For the most popular vehicles, Aeromo­tive and Holley offer replacement tanks that are closer to the $600 price range, and they use nice reproduction tanks with their own proprietary pump systems.

Ambitious builders can choose to modify the stock tank themselves. Note: The following procedure requires welding on a gas tank. Serious injury or death can occur if the utmost care and preparations are not followed. There are a several ways to alter a stock tank to take an EFI fuel pump.

The bargain-basement method is to take the stock sending unit assembly out of the tank, cut off a short section of feed line (about 1½ inches, depending on the depth of the tank and the length of the pump), and fit the pump to the stub using fuel line and hose clamps. The important thing here is to make sure the pump is mounted about 1/4 inch off the floor of the tank with a filter sock resting on the bottom of the tank. This keeps the impurities out of the pump while getting the most fuel out of the tank.

The pump needs to be sup­ported, so a piece of steel rod can be welded to the underside of the assembly plate. The pump is then clamped to the rod, so it remains stationary. This method won’t work for all tanks, espe­cially shallow tanks, and it may be hampered by the diameter of the stock assembly. Additionally, the fuel-level sending unit may be in the way, depending on the application. This method keeps the stock feed lines in place and eliminates any floor pan clear­ance issues. One more drawback is the complete lack of a fuel sump feature, which traps fuel around the pump inlet, ensuring it does not run dry. Running an in-tank pump dry is very destruc­tive; they don’t last long when run dry.

The next option involves welding on the tank. This is extremely dangerous and should not be attempted in haste or by novices. All of the old fuel must be removed and the tank thor­oughly rinsed, drained, and rinsed again until there is absolutely no possibility of any remaining fuel vapor. If you smell a hint of gas, do it again. Some people even suggest filling the tank with water or inert gas, such as argon, while the welding is being performed. In any event, when in doubt, seek the help of a professional. Most fuel tank builders offer their services for retrofitting tanks, so employ their services if you can.

Installing a custom in-tank pump in the top of the tank often requires a recessed panel on the top. The fittings clear the floor pan and provide a flat surface to mount the new assembly. If you place the top sump to the side of the original, the stock sending unit can be used, simplifying the process. This requires a boxed sec­tion be built and welded to the top of the tank. Then a fuel pump assembly unit is built with both wiring and inlet and outlet fit­tings. This piece should have a bar or rod on the inside portion of the tank for the pump to mount to.

Using 90-degree hose barb fittings is usually the easiest way to get the fuel in and out of the assembly. These fittings must be sealed tight so they don’t leak. The entire assembly bolts to the sump. In addition, by installing baffles to the inside of the tank, fuel will surround the pump at all times. These should be added before the top sump is installed.
The other option is to weld a sump into the bottom of the tank. This sump would be placed directly below the pump, but the pump would be installed in the lowered section, with the filter sock on the floor of the sump.

Tanks Inc. offers an upper tank mount, complete with a fuel pump and a baffle. This option reduces some of the legwork in building this piece and ensures the pump will be covered with fuel at all times.
There is one more option that allows you to install a truly high-performance fuel pump into a stock fuel tank without welding. Aeromotive offers two retrofit in-tank pump kits: the Phantom and the A1000 Stealth systems.
For basic street performance use, the Phantom 340 kit is suit­able. This kit allows you to sim­ply cut a hole in the top of the tank, drop in the pump, bolt it down, hook up the lines, and you are done. The kit comes with the seals, hardware, and a drill jig to ensure the holes are in the right place. The 340 supports up to 700-hp supercharged EFI engines or 1,000-hp supercharged carbu­reted systems. The Phantom sys­tem can fit in just about any tank, so this is a really good option that takes out the guesswork.

For more serious performance engines, the Stealth A1000 sys­tem feeds up to 1,300-hp EFI sys­tems and 1,500 for carbureted engines. Installing these systems takes slightly more effort than the Phantom kit, but not much.

Next, we need to make a flex line to connect the fuel line to the engine. We are using Earl’s Performance Plumbing fittings and Super Stock hose, which is a push-on style. It can handle 250 psi, good enough for our LT. We also have an adapter that will push onto the stock LT fuel rail. As a side note, always use swept tube–style fittings like this for fuel; the block-style 90-degree fittings cause turbulence in the fluid flow.

Then, the hose is just pushed onto the fitting until it won’t go anymore. These may not seem like high-pressure hoses, but they work very well. Be sure to use the Super Stock hose with Super Stock fittings for this to function correctly.

A little assem­bly lube makes pressing the hose onto the end much easier.

One end of the hose was threaded onto the adapter on the hard line. AN fittings do not require much torque, just hand tight and then a slight tightening is enough. Too much torque will damage the seal.

External or inline pumps offer a simpler installation and are usually cheaper. Inline pumps are much easier to change, mak­ing roadside swaps bearable. The main gripe over inline pumps is the noise. Drivers may hear the whir of the electric pump over the engine with a stock-style quiet exhaust. For most builders, the added noise is merely an inconve­nience. However, for a show car, a noisy pump might be considered a serious drawback.

The real drawback for an inline pump is that the fuel line is only pressurized after the pump, so the tank to the pump is grav­ity fed. Anyone who has dealt with a modern high-performance external fuel pump can tell you that life is really difficult when you lose the siphon in the tank. Simply having the pump in the tank maintains a constant supply of fuel to prevent those hard-cornering and acceleration woes that come with a stock tank and an inline electric fuel pump.

Inline fuel pumps also require a more substantial return line system. This is because of the long distance between the reg­ulator and the fuel tank. Inline pumps are also subject to failure through heat. The only thing that cools the pump is the gas flowing through it.

Not all inline pumps are cre­ated equal. External pumps come in all different shapes and sizes with the majority of the market consisting of low-pressure units designed for carburetors. These pumps deliver 6 to 14 psi, and they are not close to the 72 psi required to operate an LT engine. Inline pumps are more suscepti­ble to overheating, and most are not capable of PWM returnless operation. So, running this in a return-style system with an LT engine will result in more com­plications due to overheated fuel.

Installing an inline pump is pretty simple, but there are a few caveats. The first is to always install a prefilter before the pump, so the pump does not get clogged and ruined. A prefilter is a screen-style filter that traps the big stuff. A micron filter should be placed after the pump to catch small contaminants. Do not install a micron post filter in front of the pump (between the tank and the pump) because it will impede the gravity feed, and there will not be enough force to push the fuel through the micron filter.

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Make sure the prefilter is large enough to free-flow the fuel. A small prefilter will restrict the flow to the pump, causing cav­itation that will burn up the pump. A stock-type metal can­ister prefilter works great, but they are not pretty. Most after­market fuel pump makers have large-capacity prefilters if you want a good-looking filter. Most of the aftermarket prefilters are rebuildable as well.

We don’t want to chop off the quick-release fitting on the fuel rail, so we are using a push-on adapter. This will con­nect to the fuel rail and leave a -6 AN connection on the other side.

All done, the fuel system is now complete.

The most important aspect of any electric fuel pump is the wir- ing. In addition, it is difficult to get solid grounds because paint, rust, and scale inhibit the ground. Always be sure to remove the paint and anything else from the ground location, so there is clean metal. Electricity requires equal grounding and positive current flow. A bad ground is just as bad as a faulty positive feed. Electric fuel pumps require a lot of cur- rent. Running a relay circuit from the pump trigger lead, along with 12-gauge positive and negative wires to the fuel pump, provides ample capacity. This ensures that the pump gets the required amperage without overheating the wires. Do not run a 16- to 24-gauge primary wire to a fuel pump because it will cause a fire. All fuel pumps require at least 12-gauge power wire, and the larger pumps need 10-gauge wire. This includes both power and ground wires.

Fuel Control Module Pressure Sensor

Regardless of how the fuel sys-tem is plumbed, the factory fuel module is required for an LT-series engine to operate correctly. The ECM must know the inline fuel pressure coming into the DI pump—without it, the engine will run erratically. To send this information to the ECM, the fuel module is needed. Because of this, running the factory-style PWM control is a matter of three wires. It is easier to use the PWM system than a regulator with return line system. The factory fuel module is a learning unit; it has the ability to slightly adjust the fuel trims to match the pump it is controlling. This technology is still fairly new, so the aftermarket has not quite caught up yet. It is possible to tune the fuel module to match the pump being used in the system. A special pressure sensor in the fuel line monitors the pres-sure of the fuel, which is main-tained at 72 psi. Rather than use a regulator, the pressure is man- aged through PWM control of the pump. Essentially, the ECM uses PWM to control the speed of the pump, ensuring full pres-sure at all times with no delays. This complicates the fuel system for the LT-series engine swap. Don’t use just any old pump. The pump must be able to be PWM controlled. Before purchasing a pump, make sure it is PWM capable. Installing the PWM control- ler is relatively simple, but the fuel pressure sensor is a bit tricky. First, an inline adapter with a pressure sensor port positioned at 90 degrees or 5 to 85 degrees to the flow of fuel is needed, accord- ing to the GM manual for the fuel controller. This means that the sensor itself must be mounted either 90 degrees vertically or between 5 and 85 degrees from the vertical position. Essentially, the sensor should not be horizon-tal or below the flow of fuel. As long as the sensor is angled upward (with the terminal sitting above the fuel port) at least 5 degrees, fuel cannot pool in the sensor. This is fairly easy because there are plenty of fuel sensor adapters out there. The problem is that most of the adapters are for 1/8-inch NPT fittings and not the 10-mm threads required for the GM sensor.

Finding a 1/8-inch NPT male to 10-mm male adapter is diffi­cult. It is easier to find a -6 AN male to 10-mm adapter. To use this, you need an aluminum fuel log or Y-block fuel splitter and a -6 to 10-mm male-male adapter. This allows you to connect the sensor into the fuel system. We made one with a leftover piece of fuel rail from another project.
Wiring the PWM pump con­troller is a plug-and-play affair, but the pump wiring itself is not. There are three wires com­ing off the pump module: yellow with a black stripe, gray, and a smaller-gauge black wire. The yel­low/black wire is the ground, the gray wire is the power side, and the small black wire is the shield. If you are using a GM pump with a shield pin, connect the small black wire to that pin, but if you are using a pump without a shield pin, leave the wire unterminated and tape it to the other wires.

Because of the nature of PWM control, there is a very real poten­tial for electromagnetic interfer­ence (EMI) from other electronics in the car. To eliminate this from interrupting the control signal, the two main power control wires are twisted with a third shielding wire. This wire is grounded to the chassis near the pump.

If you want your LT engine to run like it is supposed to, use the fuel control module (FCM). This small computer controls the fuel pressure your engine receives based on demand.

There are three wires that run from the FCM to the fuel pump, and they must be twisted with a shield ground wire. We braided our wires, but the minimum is 27 twists per 8 foot. The cleaner and more consistent the twist, the better the signal wires are protected. A loose braid is best because a really tight twist or braid can stress the wire itself.

There are several ver­sions of the fuel pressure sensor that can be used with LT-series engines. Upper left is the Cor­vette and truck sensor; bottom right is the sensor used with Camaro LT engines. They are the same internally, but the Camaro sensor has hose barbs, while the other requires a 10-mm male threaded adapter.

The FCM must be mounted between the engine and the fuel tank; the Chevrolet Performance wiring harness has a very short pigtail for the FCM to fuel pump run, so it may need to be extended. On the Buick GS, we mounted the FCM under the car to the transmission crossmember.

Depending on the fuel sys­tem plumbing, the Camaro sensor may work better because the truck/Corvette sensor can become a bit clumsy if you can’t find a direct fitting adapter. If you are using AN fittings, the Corvette sensor works better.

The Chevrolet Performance wiring harness only comes with a certain length, about 6 feet. To maintain the shielding, the wires must be twisted at a minimum of 27 twists per 8 foot of wire. The best way to ensure that the wires are correctly twisted and won’t unravel is to braid the three wires together. It does not need to be a tight braid, rather a consistent loose braid, wrapping the wires around every 3 inches or so. Do not use crimp connectors for these wires. Instead, make sure to solder them well and use shrink tubing.

Return Lines

If you decide to go with a regulator/return-line setup, then you will need to run a new line. The minimum requirements for EFI fuel lines are 3/8-inch line for the feed and 5/16-inch line for the return. Some muscle cars and trucks came with return-style mechanical pump fuel systems, but these are not the norm for older vehicles—most were dead-head systems, meaning that the fuel simply stops at the pump until it is sent on to the engine.
Many people assume you can use the 1999-and-up Corvette fil­ter regulator with an LT engine, but this is not the case. While the engine will run, it will be starving the pump on the top end. This unit has two lines (an input and an output) on one side for the fuel tank, and one output on the other, which goes to the engine.

This preset regulator provides the correct 60 psi to the engine, which pressurizes the entire fuel line while pumping the excess fuel back to the tank. This is typ­ically mounted as close to the tank as possible to minimize the length of feed and return lines to the tank. This is not recom­mended for an LT engine swap. For a full dual-line system with the pump in the tank, a filter between the pump and the fuel rail is the preferred method if you are not running the factory PWM system (the filter is required for all fuel systems). It is best to filter the fuel as soon as possible, keep­ing the fuel lines clean.

Installing new lines is a fairly simple process, but it can be nerve racking at the same time. There are three ways to accomplish this task: run braided hose, bend new hard lines, or install pre-bent hard lines. Using pre-bent hard lines is the simplest method if the vehi­cle has the fuel tank in the stock location.
Pre-bent lines, such as those from Classic Tube and Tube Tech, are patterned after the original lines in the car and should fit just like the originals. That is not to say that there are not compro­mises and tweaks that must be made along the way.

Bending and installing custom lines most effectively transports fuel the length of the vehicle, but it is much easier said than done. This is a challenging task that requires some metalworking skills, and therefore the task will be frustrating at best for the nov­ice. There are tubing makers, such as Classic Tube, that offer cus­tom bending services using coat hangers or other wire. A pattern is bent by hand and sent to the maker. They, in turn, will bend a set of hard lines to your specifica­tions and ship them to you. This ensures quality bends with proper flare where you want them— without kinks—and without the aggravation of doing it yourself.

The other option is to use flex­ible hose for the long runs. This works, but braided hose should be used rather than plain rubber hose to protect from road debris damage. The chance of road debris snagging a long, braided fuel line is much higher than with a hard line. Rubber lines are not the best option either. Rub­ber lines dry out and crack much faster than hard lines corrode, so you will have to replace the rub­ber lines eventually.

The Camaro has good hard lines up to the engine bay, so we chose to use them for the fuel feed. The larger line is 3/8 inch, which will work perfectly.

We used a tubing cutter and removed the flare because we will make our own.

AN fittings require a 37-degree single flare (never a double flare), which we made using this portable tool from Matco. The standard 45-degree flare commonly used for brake and non-AN fuel lines will leak with AN fittings.

We are using a tube sleeve and nut to create an AN flare for the pressure sensor. These are from Earl’s Per­formance Plumbing and are -6 AN, which is the correct size for 3/8-inch line. The tube nut goes on first, then the sleeve, then flare the line.

Once flared, the sleeve slides up to the flare. The nut will thread onto the fitting, creating a tight seal.

We installed the fitting, which is an adapter port for the pres­sure sensor.

Written by Jefferson Bryant and republished with permission of CarTech Inc

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Regardless of the application, if you’re building or rebuilding an LS engine from scratch and intend to boost horsepower, it just makes sense to purchase a set of forged pistons to eliminate the potential variable. Aftermarket performance piston manufacturers offer a wide selection of forged pistons for the LS engine format, in a variety of popular bore sizes, compression heights, and compression ratios. Check brands such as JE, Wiseco, Diamond, Ross, CP, and others.

Piston Compression Height

Compression height, also called compression distance or piston CD, refers to the wrist pin bore centerline to the piston deck. If you’re planning to build a stroker engine, the combination of crankshaft stroke, block deck height, connecting rod length, and piston compression height is relative to the piston deck’s location to the block deck at top dead center (TDC).

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As an example, let’s say that the block deck height is 9.240 inches, which is the GM factory spec for LS deck height. Block deck height refers to the distance from the main bore centerline to the block deck. However, OEM blocks are rarely machined properly. The raw block may be slightly less or slightly more than 9.240 inches, decks may be finished nonparallel to the main bore centerline, and deck height may differ from the front to the rear of the block. The block should be corrected prior to selecting components to verify the final corrected deck height. But for the purposes of theory, let’s say that our block’s deck height is 9.240 inches.

For the purposes of this example, our crankshaft stroke is 4.000 inches. To determine where our piston dome will be located relative to the block deck, we need only factor half of the crankshaft stroke, from the rod journal’s top-dead-center location to the block deck. So, in this case our stroke factor is 2.000 inches. At this point we know that 2.000 inches of our 9.240-inch deck height is taken up by the crank stroke. The remaining theoretical distance of 7.240 inches must be achieved by the combination of our connecting rod length and our piston compression distance. Rod length refers to the distance from the centerline of the rod big end to the centerline of the rod’s small-end bore. By selecting a rod length of 6.125 inches, this leaves a required piston compression distance of 1.115 inches. Formula:

1/2 Stroke + Rod Length + Piston CD = Block Deck Height

In this example:

2.000 + 6.125 + 1.115 = 9.240

This would theoretically place our piston dome flat flush with the block deck.

With block deck height, crank stroke, and rod length already known, to determine piston CD is easy using the following formula:

Block Deck Height – (1/2 Stroke + Rod Length) = Piston CD

Using the previous example:

9.240 – (2.000 + 6.125) = 1.115

Aftermarket performance forged pistons may be ordered in a range of compression distances. Some piston makers offer a specific range of compression heights, while some makers will custom-machine your pistons to whatever compression height you require, as long as the pin bore will not intersect the second compression ring groove.

If the block decks have been machined to a height less than 9.240 inches, the pistons may protrude a few thousandths above the decks. To obtain adequate piston-to-valve clearance, these clearances must be checked, factoring in total valve lift and cam duration, rocker arm ratio, intake and valve diameters for radial clearance, and thickness of the cylinder head gasket. If during test fitting and measuring, valve clearance is not adequate, a thicker head gasket may be selected to compensate. Another option is to have the piston dome’s valve pockets milled to a larger radius if the valve head diameter is a tick too large for radial clearance. As far as valve-to-piston clearances are concerned, a minimum recommended clearance for intake valves should be .080 inch, with a minimum of .100 inch for the exhaust valves. This clearance is even more of a concern with an aluminum block, which has a greater potential for thermal expansion.

When checking valve clearance with head gaskets installed, the gaskets must be crushed as they would be during final assembly. Multi-layer steel (MLS) head gaskets can easily be measured for thickness by measuring thickness adjacent to the gasket rivets, where the layers are already fully compressed. MLS gaskets are available in a variety of thicknesses, generally in the .041- to .045-inch range. However, some gasket makers, such as Cometic, can supply custom MLS gaskets in a much wider range of thicknesses. For example, if a compressed gasket thickness of .045 inch does not provide adequate clearance, a gasket thickness of .051 inch may be obtained. This is just an example.

Before ordering oversize pistons, it’s wise to measure the cylinder wall thickness in all cylinders using an ultrasonic thickness gauge. This will aid in determining how far the boring/honing oversize can go. Measure at a variety of bore height and clock positions, as wall thickness may vary.

To place the piston at TDC relative to the block’s deck height, with certain crankshaft stroke and rod length variables, the piston compression height may dictate that the pin bore be raised, intersecting the oil ring groove. This requires the use of an oil ring support rail that completes the footprint for the oil ring package over each end of the pin bore.

A dial indicator aids in measuring the precise top-dead-center (TDC) position of the piston. With the piston at TDC, a depth micrometer can be used to measure deck height relative to the block deck, to determine if the piston is below, flush with, or above deck.

The support rail features a male pimple that prevents the rail from rotating and may prevent placing the rail gap at one of the two relief areas. When installing the rail, the male dot must be placed at either relief opening. Support rails are included in the oil ring package for pistons that require these rails.

Depending on stroke and rod length, a shorter piston CD may be required to keep the piston flush or just below the block deck. In many cases, shortening the piston CD, which involves moving the wrist pin bore upward, results in the pin bore intersecting with the oil ring groove. In this case, the oil ring groove will have been machined taller to accommodate both the oil ring package and a “support rail,” which serves to complete the footprint for the oil ring package at each side of the wrist pin bore.

Bore Size, Dome, and Compression Ratio

The available combinations of cylinder bore diameter, piston dome shape, and static compression ratio for LS engine applications are quite extensive. The standard bore size for LS1 and LS6 formats is 3.898 inches. The standard bore size for LS2 is 4.000 inches. Bore size for LS3 is 4.065 inches, and LS7 standard bore size is 4.125 inches. Oversizes are available in a variety of diameters, depending on whether the block is a standard bore and whether it is an iron or an aluminum block. While iron blocks allow a degree of overboring, aluminum blocks with their integrally cast-in sleeves allow for only a slight bit of honing oversize. For example, an aluminum LS1 or LS6 block will accept an oversize up to only around 3.905 inches. Aluminum LS2 blocks will accept honing oversize to about 4.030 inches. LS3 aluminum block cylinder bore oversizing is limited to about 4.080 inches. LS7 blocks may be oversized to about 4.130 inches. Iron blocks may accept a further increase, but cylinder walls should first be measured for thickness using an ultrasonic thickness gauge to verify the minimum available wall thickness. Finished wall thickness generally should be limited to a minimum of about .180 to .200 inch. Again, as a generalization, an LQ9 6.0L iron block should accept an overbore of .060 inch, although an overbore of .030 inch would be safer.

An example of a flattop piston dome. Depending on the cylinder head combustion chamber volume, choosing piston dome volume in combination allows you to tailor the desired compression ratio.

If you plan to use forced induction to boost cylinder pressure, stay away from a theoretically minimum wall thickness. The thicker, the better. Because of the tolerances involved in both aluminum block cast-in cylinder liners and iron block castings, cylinder wall thickness may not be uniform from top to bottom or around the circumference of the bores. Before oversizing, measure existing wall thickness from top to bottom and at a variety of clock positions on each cylinder location.

Off-the-shelf dome configurations include flattop, inverted dome, and domed. Flattop pistons will feature intake and exhaust valve relief pockets. Inverted dome pistons feature a relieved dome “bowl,” while domed pistons feature a raised dome area. Obviously, the volume of the dome affects compression ratio. Inverted domes provide a lower compression and domed provide a higher compression ratio. Obtaining the desired compression ratio is not limited to the piston itself. The combination of piston dome volume and cylinder head combustion chamber volume work in unison to create static compression ratio.

High-dome pistons obviously create a smaller combustion chamber volume, increasing compression ratio compared to a flattop dome.

Piston makers offer comprehensive charts that list the cubic-inch displacement and static compression ratio for any given combination of cylinder bore diameter, crank stroke, rod length, piston compression height, block deck height, piston dome volume, and combustion chamber volume.

While we don’t have the space here to list all possible combinations for all LS platforms, citing an LS2 aluminum block as an example, a cylinder bore oversize of 4.005 inches coupled with a crank stroke of 4.000 inches would provide 403 ci of displacement. To mate with the 9.240-inch block deck height, rod length would be 6.125 inches and piston compression height would be 1.115 inches.

Using a flattop piston with a dome volume of –5 cc and a cylinder head with a combustion chamber volume of 64 cc would provide a compression ratio of approximately 11.6:1. With a combustion chamber volume of 68 cc, compression would be about 11.3:1. With a 70-cc combustion chamber, compression would be about 10.8:1.

An example of an inverted dome piston for an LS3 application. The JE forged piston shown here features a .097-inch-deep inverted dome and 12-degree valve relief pockets. The lines you see here are simply surface shadows left by the CNC-milling under studio lighting. The dome surface is actually flat and smooth. Dome volume is –14.6 cc. Using an inverted dome allows a reduction of compression ratio compared to a flattop piston.

Using the same combination of parts but with an inverted dome piston that has –7.6 cc of volume, using a 64-cc combustion chamber would provide about 10.9:1. With a combustion chamber of 68 cc, compression would be about 10.5:1. With a 70-cc combustion chamber, compression would be about 10.3:1.

Again, using the same above combination but with a domed piston that has 5.0 cc of volume, a 64-cc chamber would provide about 13.2:1. A 68-cc chamber would provide about 12.5:1, and a 70-cc chamber would provide about 12.2:1. Depending on bore size, piston dome configuration, and cylinder head combustion chamber volume, pistons for LS applications may be selected to achieve anywhere from about 8.1:1 to 13.2:1 static compression ratio.

Keep in mind that if you plan to run forced induction, the static build compression ratio will dramatically increase at effective compression when boost is added. For example, with a Roots-style supercharger, a static ratio of 8.0:1 can rise to an effective ratio of 11.3:1 with only 6 psi of boost, and to more than 15.6:1 with 14 psi boost. Generally speaking, for street applications running aluminum heads and 92 octane fuel, you should try to keep effective compression to about 12:1 maximum. Suggested limit examples are as follows:

Piston Selection of KS7 Flattop Pistons

To demonstrate piston selection based on stroke, bore diameter, rod length, piston compression height, and cylinder head combustion chamber volume, following are examples of LS7 flattop pistons that feature a dome volume of –2 cc. Note: “CD” stands for piston compression distance and “CR” stands for compression ratio. All results are based on a block deck height of 9.240 inches. To illustrate one piston maker’s offerings, all examples here are listings by JE Pistons.

The following examples are based on LS2/LS3 builds, with choices of three different cylinder head combustion chamber volumes. Bear in mind that an incredibly diverse selection of pistons is available for these applications. Here I’ve listed only a few. These examples feature flattop pistons with a dome volume of –5 cc.

As noted, the examples from JE Pistons represent only a small number of build variations. Depending on stroke, bore diameter, rod length, piston compression height, combustion chamber volume, and piston dome volume, off-the-shelf forged pistons are readily available to achieve compression ratios of 8.0:1 to 13.2:1. Obviously, flattop or inverted dome pistons and/or larger combustion chambers can achieve lower compression ratios. Whole higher ratios can be had with small combustion chambers and/or higher-domed pistons.

Skirt-to-Wall Clearance

The engine block’s cylinder bores should never be final-finished until you have your intended pistons in hand. The piston skirt diameter dictates the required finish-honed bore diameter. Measure skirt diameter and add the wall clearance recommended by the piston maker to finish-hone the bores. It is critical to measure the piston skirts at exactly the location specified by the piston maker because piston skirts feature a very slight taper. As an example, JE forged pistons are usually measured exactly .500 inch from the bottom of the skirt, unless the measuring location is specified otherwise. The measuring point varies depending on the specific piston design. Add to this the recommended piston clearance to final-hone the cylinders. It’s important to note that piston diameters are not measured at the ring area, but at a specific point on the skirts. A general rule of thumb for forged pistons is .001-inch clearance for every inch of cylinder bore diameter. For example, a 4.000-inch bore would require .004-inch piston-to-wall clearance. Again, this is a generic specification. Always adhere to the clearance recommendation provided by the piston maker.

Before finishing the cylinder bores to size, the piston skirt diameter must be measured to determine the bore diameter required for the recommended piston-skirt-to-wall clearance. It is critical to measure only at the skirt area specified by the piston maker.

Piston and Rod Orientation

The installed direction of pistons to connecting rods is critical. Let’s consider the rod orientation. If the big end of the connecting rod features a larger chamfer on one side, this side must be installed facing the crankshaft’s journal radius fillet. If the rods are designed for use on a crank that does not feature a radi-used fillet, the rods may not feature a large chamfer on one side.

Valve pockets can be used as reference as well when orienting the pistons. The larger intake valve pocket faces the front of the engine on the left-side cylinder head, while the intake valve pocket faces the rear of the right-side head.

Original equipment hypereutectic flattop pistons feature a dot on the dome. The dot indicates that the piston is installed with the dot facing the front of the engine on the right bank and with the dot facing the rear of the engine on the left bank.

If there is no noticeable chamfer on either side of the rod big end, the bearing placement on the side of the rod that faces the fillet should be slightly spaced away from the fillet to prevent the bearing from digging into the fillet radius.

Skirts and Major/Minor Thrust

The shape, area of mass, and weight of a piston’s skirts play a major role in managing friction and in stabilizing the piston during TDC and BDC transitions. Here we’ll discuss the role of the major and minor thrust sides of a piston and the development of asymmetric skirt designs intended to minimize weight while maximizing efficiency.

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Piston skirts are not perfectly round, and each side of the piston experiences different levels of loading relative to the intake and exhaust sides of the cylinders. Skirt design plays a major role in accommodating these forces in ways that improve durability and performance; so does piston weight. The piston skirt area is slightly barrel shaped to provide an adequate surface load against the cylinder wall while reducing friction. The amount of surface area must accommodate the load while providing piston stability to minimize rocking relative to the pin axis as the piston moves down from TDC and back up from BDC. The piston experiences a “major” and “minor” thrust force at opposing sides of the piston skirts. The major thrust face is the side of the piston that receives the thrust on the power stroke. As viewed facing the front of the engine, if the crankshaft is rotating clockwise, the major thrust face is on the left side of the cylinder (the exhaust sides of the right/passenger-side cylinders; and the intake sides of the left/driver–side cylinders). The minor thrust side experiences force on the compression stroke.

This piston’s minor thrust side skirt design provides great contact and support for the thrust side where it’s needed, and a small skirt for the minor side, where it’s less critical, saving weight in the process.

This difference in force at each side of the piston is caused in part by the operating angles of the connecting rod during its travel. During the firing cycle, the load experienced on the major thrust side skirt can be as much as 10 times greater than the load experienced on the minor thrust side skirt. The difference in skirt loading will vary depending on variables such as crankshaft stroke, connecting rod length, and peak cylinder pressures.

Asymmetric pistons are bank specific, and thus each piston is labeled for right or left bank position. The dome may also feature a laser-etched arrow that indicates piston orientation toward the front of the engine.

Asymmetric pistons feature a wider skirt at the major thrust side and a smaller skirt at the minor thrust side. The underside view clearly shows the difference.

Major Thrust Side

When the piston is pushed down during the power stroke, it experiences resistance as it attempts to turn the crankshaft. As load increases, the amount of resistance increases. During this resistance, the piston side load is forced to one side, and that’s the major thrust side. It places more force and subsequently increased friction and potential wear on the thrust side of the cylinder wall. If the piston dome features a reference dot or other orientation mark, it’s critical to install the piston with this mark facing the appropriate direction. Usually the mark indicates the side of the piston that should face forward. The piston side loads on the major side tend to increase with the use of a longer stroke and with forced/boosted induction pressures. Again, assuming a clockwise-rotating crankshaft, the major thrust side will be at the exhaust side of the engine’s right bank and the intake side of the left bank.

Minor Thrust Side

The piston’s minor thrust side is directly opposite the major thrust side. The minor thrust side is forced to the opposite side of the cylinder wall as it moves up on the compression stroke by the resistance generated by meeting the air/fuel mixture. The role of the minor thrust side is basically to provide piston stability, with the major thrust side taking the brunt of the cylinder wall contact. Due to its “less force” role, the minor thrust side skirt can be narrower, saving weight without sacrificing strength.

To address, or “fine-tune,” these forces between the major and minor thrust sides, asymmetric pistons have been developed that feature two different-size skirts.

This style of piston is specifically designed with a larger (wider) skirt on the major thrust side and a smaller skirt on the minor thrust side. This provides a greater “footprint” for the major thrust side, where it’s needed the most to handle a higher degree of thrust loading, and allows the piston weight to be slightly reduced by featuring a small footprint on the opposite/minor thrust side, where the force is less. During the power stroke, when the piston changes direction at top dead center, combustion pressure pushes the piston down and at the same time pushes the thrust side of the skirt toward the cylinder wall.

Citing JE Pistons’ “asymmetric” design as an example, in its forged side relief (FSR) line, a wider skirt area is featured on the major thrust side, and the pin bosses are relieved at the outboard sides to allow the use of a shorter (and lighter) wrist pin.

The asymmetric design approach was initially developed for specific racing applications, but the concept has trickled down to street applications, with the LS platform as a good example.

Another benefit to the asymmetric approach is increased piston ring sealing and ring stability thanks to the skirt mass and profile. Basically, the dedicated major and minor thrust skirt design coupled with a slightly offset wrist pin directly addresses ring performance in addition to reduced wall friction.

Offset Pin

Asymmetric pistons also feature an offset wrist pin, with the pin centerline biased from zero toward the major thrust side by .020 inch. This slight offset tends to balance the piston to accommodate the difference in skirt mass and to compensate for and alter the effect of rod angle, transferring a bit of force away from the major thrust side.

This finite element analysis (FEA) view shows even stress forces at both major and minor thrust sides (note the dark dome areas), even though skirts differ in area. The offset location of the wrist pin aids in balancing out the pivot point. (Photo Courtesy JE Pistons)

FEA takes a snapshot of the piston’s stress levels at the worst-case scenario, which differs greatly from an engine that’s at part throttle. The image plots the stress level. The high-stress areas are shown in red in accordance with the chart on the right. This is a simulation of stress under firing. (Photo Courtesy JE Pistons)

Again citing JE’s development in this area, the asymmetric design allows the use of shorter, stiffer, and lighter wrist pins. According to JE, a typical weight savings is about 10 grams.

Note: The contact pressure FEA images here show contact pressure specifically between the skirt panel and the bore. It’s important to analyze both skirt profiles on an asymmetrical piston design even though the minor thrust experiences much less pressure. On a symmetrical design, typically only the major thrust is analyzed. Stress images show how the stress at the skirts affects the rest of the piston.

The stress of the piston under major stress. (Photo Courtesy JE Pistons)

Piston Coatings

A variety of coatings is available for both internal and external engine components, with applications varying from power enhancement, engine efficiency, and durability/longevity to corrosion protection and external appearance. Here we’ll focus on coatings that apply to pistons. Today’s coatings include those designed to reduce friction and enhance lubricity and thermal barrier coatings for increased engine efficiency and protection of components exposed to extreme heat levels.

Thermal Barrier Coatings
Thermal barrier coatings (which are intended to serve as a heat shield) feature a ceramic formulation designed to prevent excess heat from passing into and being absorbed into the piston domes. This theoretically increases combustion efficiency and reduces piston dimensional changes that may occur due to thermal expansion.

The specific formulas differ depending on the coating manufacturer and the application. Specialized thermal barrier coatings applied to piston tops aid in reflecting heat, reducing the amount of piston expansion (allowing the builder to maintain more consistent wall clearance), and protecting the piston from extreme temperatures encountered in forced-induction systems. For forced-induction and nitrous applications, highly specialized thermal barrier coatings are available not only to enhance combustion efficiency but also to protect the piston from potential heat-related damage.

Bear in mind that the quality of application of a ceramic coating (especially for internal engine components) is extremely critical. The last thing you want is for hard and potentially damaging ceramic to break loose and contaminate the engine. That’s why you need to use established coating services, such as those offered by Swain Tech Coatings, Polydyn, and others. When properly applied, the coating not only adheres to the applied surfaces but permanently bonds to the material, essentially becoming part of the base material. If substandard application practices are used, the coating may not be fully bonded and could flake off. In other words, don’t try this at home.

While building engines for 24-hour endurance racing, I’ve had many dozens of engine build components ceramic coated (heads, pistons, valves, exhaust) with absolute success, but I’ve seen a few devastating issues with components that were “coated” by inexperienced mom ’n’ pop shops that caused serious damage. Don’t be afraid of ceramic internal coatings; the top shops do an outstanding job, and they know what they’re doing. Don’t be tempted to go for bargain-basement services.

Anti-friction piston skirt coatings are available already installed on new pistons, as shown in this example, or by sending your pistons to a specialty coating service.

Anti-Friction Coatings

Anti-friction coatings are applicable to surfaces that make or potentially make contact, such as (but not limited to) main bearings, rod bearing, cam bearings, and piston skirts. Anti-friction coatings, also called lubricity coatings, provide a temporary lubricity when/if the surface is starved for oil, upon cold starts, and during piston rock when transitioning from top dead center to bottom dead center. This type of protective coating also serves to improve oil retention on the surface. While specific antifriction coating formulas vary among the coating services, the materials are generally composed of moly-, graphite-, or Teflon-based materials. The intent is to provide better oil retention and to provide a super-slippery surface.

Specialty coating options for pistons include a thermal barrier dome coating, anti-friction skirt coating, or both.

Piston skirt coatings are generally applied at an average thickness of about .0005 inch per side, which might provide about a .001-inch increase in piston overall skirt diameter. The moly has been applied in such a thin layer, no additional bore dimension changes are required to run “moly-coated” pistons. Unless otherwise instructed by the piston maker, do not compensate for the added moly coating when finishing your bores. A specialty coating service may apply anti-friction piston skirt coatings or, depending on the piston manufacturer, new pistons are often available with the coatings already applied. While you may or may not need a skirt coating, there’s no downside to this application. A skirt coating won’t hurt, and it may very well help to prevent skirt wear when called upon.

Written by Mike Mavrigian and republished with permission of CarTech Inc

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The post How to Choose Performance Pistons for Gen IV LS Engines appeared first on LS Engine DIY.

The camshaft is one of the major determining components of the effective operating range of the engine. Of course, cam timing must be combined with the proper intake manifold, head flow, and primary length on the exhaust for optimum operation over a given RPM range, but the right cam can almost determine the character or personality of the engine. Stock or ultra-mild aftermarket cams provide a dead-smooth idle, while more radical grinds can transform that mild-mannered LS engine into one radical ride.

The factory LS3 is a common upgrade for 4.8 and 5.3 applications because those lesser LS engines were equipped with the mildest factory cams ever offered. Of course, the high-performance LS7 was factory equipped with the most powerful cam ever offered on an LS, but the stock stuff is just begging to be replaced.

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The LS3 and LS7 are fantastic engines, offering an impressive combination of power, reliability, and even fuel mileage. Another area where they excel is how well they respond to performance upgrades, especially camshafts. These factory performance engines respond so well to wilder cam timing because they have everything else required to make power, including displacement, intake, and head flow. All that is lacking to dramatically improve the power output of a typical LS3 or LS7 is cam timing.

The single best (and most powerful) modification you can make to your LS3 or LS7 engine is a cam swap. These engines already feature a good intake and plenty of head flow, so all they need to make amazing power is more aggressive cam timing.

With the factory heads and intake already capable of supporting more than 600 hp (700 hp on the LS7), mild cams are definitely the limiting factor. Given this situation, cam upgrades for LS applications have become hot sellers. Plop just about any cam in an otherwise stock LS and watch the power soar. I have seen power gains of 65 to 70 hp from a simple cam swap on an otherwise stock LS application. The gains can be even greater higher in the rev range.

There is, of course, a limit to how wild you can go with cam timing on an otherwise stock LS (3 or 7) engine. Although the LS duo certainly responds to more aggressive cam timing, two limitations are inherent in the stock combinations. First, stock valve springs were designed for stock cams and are, therefore, insufficient for performance use. From available valve lift and RPM potential standpoints, spring swaps are not just a good idea, they should be considered mandatory for most cam upgrades on an LS3 or LS7.

The other limiting factor in terms of cam timing on a stock LS3 or LS7 application is available piston-to-valve clearance. Although lift plays a minor role, the real culprit in piston-to-valve clearance is duration (how long you hang that valve open). Each successive increase in duration (the intake hits before the exhaust) decreases the available clearance. Cams that exceed 230 degrees of intake duration should always be checked, especially if they were ground with a few extra degrees of advance.

One of the most common questions regarding camshafts is which one is right for your LS combination. The term “right” here obviously has different meanings for different people, so choosing the so-called right cam can be difficult for even cam experts. The difficulty comes not in the technical nature of cam timing or profiles, but in deciphering exactly what you want. This becomes even more difficult when you are unsure.

LS cams are available in single- and three-bolt configurations. If you are upgrading an LS3 and select a three-bolt cam, make sure you have the matching three-bolt cam gear

Asking enthusiasts what cam they want is a little like asking them how much power they want. The problem is that they want as much power as possible and they also want a factory-smooth idle, 50 mpg, and maintenance-free operation. It goes without saying that it is not possible to combine all of those elements. Obviously that is a lot to ask of any camshaft and, ultimately, trade-offs become necessary. The question then becomes how many of the trade-offs you are willing to accept in your quest for power. Luckily for LS3 and LS7 owners, it doesn’t require much in the way of cam timing to make a major difference in power.

Factory hydraulic roller lifters work well, but there are aftermarket performance units available, including retrofit, short travel, and even solid roller versions.

The factory LS3 and LS7 feature offset intake rockers. The LS3 shares the 1.7-ratio, exhaust rocker with cathedral-port LS applications, but the 1.8-ratio LS7 is specific to that cylinder head configuration.

Test 1: Stock LS3 vs Comp Cams 281LRR on a Modified LS3

Cam swaps are popular for the LS family, especially the LS3, for good reason. Nothing adds power to an LS3 like a cam swap. Short of power adders or a stroker engine, no modification equals the power gains offered by a cam swap. This is because an LS3 already has sufficient displacement, intake, and (especially) cylinder head flow to make serious power. The only thing missing from the combination is cam timing. Add the right cam to an LS3 and watch the power needle climb.

The power gains are even more impressive when you further increase the power potential with ported LS3 heads such as the ones from Chevy Performance run on this LS3 crate engine. Chapter 2 illustrated that an added ported head to a stock engine offers very little in the way of extra power, but adding a cam to a combination with ported heads shows big gains.

This test engine was a GM Performance LS3 crate engine from Gandrud Chevrolet upgraded with GM Performance CNC L92 heads, ARP head studs, and a manual throttle body. The LS3 also featured Lucas 5W-30 synthetic oil, long-tube headers, and a Holley Dominator EFI management system.

Run first with the stock LS3 cam, the LS3 produced 503 hp at 5,500 rpm and 497 ft-lbs of torque at 4,600 rpm. The GM Performance L92 heads were supplied with stock LS3 springs, so it was necessary to install a set of dual springs from BTR to test the cam. After replacing the stock LS3 cam (and springs) with the Comp 281LRR cam (.617/.624 lift split, 231/239 duration split, and 114 LSA), the peak numbers jumped to 569 hp at 6,500 rpm and 522 ft-lbs of torque at 5,200 rpm. There was little change in power below 4,000 rpm, but the gains increased thereafter with engine speed.

The stock LS3 cam featured a single-bolt for the cam gear, but the Comp cam was a three-bolt design (Comp offers single-bolt cams as well). The three-bolt cam requires a 4X, three-bolt cam gear.

Here are the stock, single-bolt, 4X LS3 cam gear; the 4X three-bolt (LS2) gear; and an early 0X truck gear (cam sensor in rear of cam).

Stock LS3 vs Comp Cams 281LRR on a Modified LS3 (Horsepower)

Stock LS3 Cam: 503 hp @ 5,500 rpm Comp 281LRR Cam: 569 hp @ 6,500 rpm Largest Gain: 70 hp @ 6,400 rpm

The most amazing thing about the power generated by the Comp cam swap was not that it added a ton of power (it did), but that the amazing gains came with no loss in power at 3,000 rpm. The gains from the cam swap increased with engine speed and peak with 70 hp at 6,400 rpm.

Stock LS3 vs Comp Cams 281LRR on a Modified LS3 (Torque)

Stock LS3 Cam: 497 ft-lbs @ 4,600 rpm Comp 281LRR Cam: 522 ft-lbs @ 5,200 rpm Largest Gain: 57 ft-lbs @ 6,100 rpm

What I like about adding a cam to an LS3 combination is that the amazing top-end power gains come with no penalty in low-speed torque. In fact, torque gains occurred just below 4,000 rpm and increased with engine speed. Larger cam profiles start to trade off low-speed torque for possible gains in peak power.

Test 2: Stock LS3 vs BTR Stage IV on an LS3

Adding just about any performance cam (and springs) to a stock LS3 is going to get you a lot of extra power, but adding the right cam can offer even more. To illustrate the gains possible with a cam-only upgrade on a stock LS3, I installed the Gandrud Chevy LS3 crate engine on the dyno and treated it to a Stage IV cam from BTR. Right at the limit of available piston-to-valve clearance, the Stage IV cam was the perfect candidate to work with the stock LS3 heads.

Remember, even in stock trim, an LS3 has an excess of cylinder head flow. The stock heads are capable of supporting nearly 700 hp on the right application (see Chapter 2), so the only thing missing in the combination is cam timing. It is also important to remember that not all cam-only upgrades are created equal and that most (like this one) must be combined with appropriate valve springs (these came from BTR as well).

The Gandrud crate LS3 was installed on the engine dyno and run with the stock cam using long-tube headers, a Holley HP management system, and Lucas oil. Also present was a FAST (manual) throttle body, Meziere electric water pump, and K&N oil filter. Run with the stock LS3 cam, the LS3 produced 496 hp at 5,800 rpm and 488 ft-lbs of torque at 4,700 rpm.

Replacing the stock cam with the Stage IV from BTR also required swapping out the single-bolt, 4X cam sprocket for a three-hole, 4X version. After installation of the new cam, the power output jumped to 570 hp at 6,500 rpm and 522 ft-lbs of torque at 5,300 rpm. Not only was peak power production way up, but the cam swap netted torque gains all the way down to 3,000 rpm. Below 4,500 rpm, the BTR cam offered an extra (and consistent) 20 to 25 ft-lbs of torque, but this number increased substantially above 4,500 rpm.

The stock LS3 (flat-top) piston features no intake or exhaust valve reliefs. Available piston-to-valve clearance is the limiting factor in terms of cam timing on a stock LS3.

Although BTR offers cam profiles that require no spring upgrades, this Stage VI cam was combined with a dual-spring upgrade.

Stock LS3 vs BTR Stage IV on an LS3 (Horsepower)

Stock LS3 Cam: 496 hp @ 5,800 rpm BTR Stage IV Cam: 570 hp @ 6,500 rpm Largest Gain: 90 hp @ 6,600 rpm

As much as I liked the huge peak power gains (74 hp) and extra 90 hp at 6,600 rpm, I also liked the fact that the BTR Stage IV cam offered gains down low. You know you have made the right cam choice for your application when you get huge power gains with no trade-offs in low-speed torque.

Stock LS3 vs BTR Stage IV on an LS3 (Torque)

Stock LS3 Cam: 491 ft-lbs @ 4,700 rpm BTR Stage IV Cam: 522 ft-lbs @ 5,300 rpm Largest Gain: 67 ft-lbs @ 6,400 rpm

Adding as much as 90 hp to an LS3 is an amazing thing, but it is the extra 25 ft-lbs down at 3,700 rpm that will be used more often in daily street driving. The extra 20–25 ft-lbs of torque up to 4,500 rpm will be most helpful in getting this LS3 up on the cam.

Test 3: LS9 vs LJMS Stage 2 Turbo on a Short-Stroke LS3

As you saw in the first two tests, cam timing is important for LS3 applications, but nowhere is it more important than on a turbo application. Spool-up of the turbo is a function of the power output of the engine at the desired spool RPM. The greater the power output, the quicker the spool-up. Things that can alter spool-up include displacement, cam timing, and intake design.

Small-displacement engines have more difficulty spooling up turbos (especially large ones), as do wilder cam timings (that may sacrifice low-speed torque) and short-runner intakes (that also reduce torque production lower in the rev range). This test illustrated the power gains offered by a cam swap on a short-stroke, LS3 turbo combination equipped with a short-runner, Holley Hi-Ram intake and large, 76-mm Precision turbo (meaning it had three strikes against it in terms of spooling). Thus, cam selection was even more critical on this engine than a stock LS3.

The short-stroke turbo engine featured an aluminum LS3 block equipped with a 4.8 crank, 6.30-inch forged Lunati rods, and custom JE pistons. The combination also included Total Seal rings, TFS Gen X 255 heads, and a Holley Hi-Ram intake (with 102-mm FAST throttle body). Rounding out the package was a Moroso oiling system, ATI dampener, and custom DNA turbo manifolds. The manifolds fed a single Precision 76-mm turbo, a CX Racing ATW intercooler, and TurboSmart 45-mm Hypergate waste gates.

The engine was first run (on the waste-gate springs) with an LS9 cam. So equipped, the turbo combination produced 697 hp and 598 ft-lbs of torque. After installation of the LJMS Stage 2 Turbo cam, the power numbers jumped to 733 hp and 621 ft-lbs of torque, but the real story is how much extra low-speed torque the cam swap offered. The gains would be even greater had I elected to equalize the boost pressure because the boost dropped by .5 psi after the cam swap (I ran it on the spring).

The test engine was an LS3 block equipped with a 4.8 crank, 6.3-inch Lunati forged rods, and JE pistons. The short-stroke LS3 was topped with a set of TFS Gen X 255s, a Holley Hi-Ram intake, and a custom turbo kit that featured stainless manifolds from DNA feeding a Precision 76-mm turbo.

Adding a turbo to the max-performance build makes cam selection even more important.

LS9 vs LJMS Stage 2 Turbo on a Short-Stroke LS3 (Horsepower)

LS9 Cam: 697 hp @ 6,900 rpm LJMS Stage 2 Turbo Cam: 733 hp @ 6,600 rpm Largest Gain: 34 hp @ 6,600 rpm

In some instances, a cam swap offers substantial power gains at higher engine speeds. Replacing the most powerful factory cam available (the LS9) with an LJMS Stage 2 turbo cam resulted in peak power gains as well as gains through the entire rev range. The cam swap also dropped the boost pressure by as much as .5 psi. More power with less boost is always a good thing.

LS9 vs LJMS Stage 2 Turbo on a Short-Stroke LS3 (Torque)

LS9 Cam: 598 ft-lbs @ 5,600 rpm LJMS Stage 2 Turbo Cam: 621 ft-lbs @ 5,500 rpm Largest Gain: 61 ft-lbs @ 3,800 rpm

The extra 34 hp was obviously welcome, but it was the extra 60 ft-lbs down low that really made this LJMS cam a success. By increasing the low-speed torque production (actually through the entire curve), the LJMS cam would certainly offer increased boost response on the street (or strip). The artificial load from the engine dyno negates some of the gain, but boost response with the turbo cam would be greatly enhanced with an extra 60 ft-lbs on tap.

Test 4: NA vs BTR Stage IV Blower Cam on an SC LSX

Building a performance LS engine means using the right tool for the right job. This applies to more than just a torque wrench or feeler gauges; it applies to running the proper cam grind for the intended use and application. In this case, the application was a supercharged B15 LSX engine. Built by General Motors to withstand 15 psi (the 15 in B15), the forced-induction combo (not just blowers) featured a forged crank and pistons (powdered metal rods) along with six-bolt LSX LS3 heads.

Add a boost-friendly static compression ratio of 9.0:1 and you have the makings of the perfect combination for a supercharged cam test. All I did was add a Whipple supercharger, 150-pound injectors, and a Holley HP management system and I was ready to roll.

This test was designed to compare an NA cam to a dedicated blower grind on a supercharged LS3 application. In addition to being designed for a positive-displacement blower application, the Stage IV cam from BTR was also slightly more aggressive. The NA cam (from Comp Cams) spec’d out with a .617/.624-inch lift split, 231/247-degree duration split, and 113-degree LSA. By comparison, the BTR blower cam offered the same lift split, an extra 8 degrees of intake duration, 11 degrees of exhaust duration, and 6 degrees of LSA (113 vs 119).

Equipped with the NA cam, the Whipple Supercharged LSX produced 855 hp at 6,700 rpm and 713 ft-lbs of torque. After installation of the BTR Stage IV cam, the peak numbers jumped to 880 hp and 714 ft-lbs. The milder NA cam actually offered more power up to 4,800 rpm, but the BTR cam pulled away thereafter. Interestingly, the boost was higher with the BTR cam than with the NA cam, despite no change in pulley size.

This test was run on a B15 crate engine equipped with a 3.3 Whipple supercharger.

Even with the blower, the cam swap was easy. Run with the (plenty powerful) NA cam, the supercharged combo produced 855 hp and 713 ft-lbs of torque.

NA vs BTR Stage IV Blower Cam on an SC LSX (Horsepower)

NA Cam: 855 hp @ 6,700 rpm BTR Blower Cam: 880 hp @ 6,700 rpm Largest Gain: 29 hp @ 6,500 rpm

Although designed for an NA (rectangular-port) application, the Comp cam offered plenty of power on the supercharged LSX. The tighter LSA and shorter duration on the NA cam offered more power down low on the supercharged applications, but the wilder Stage IV BTR cam came on strong at the top of the rev range.

NA vs BTR Stage IV Blower Cam on an SC LSX (Torque)

NA Cam: 713 ft-lbs @ 4,600 rpm BTR Blower Cam: 714 ft-lbs @ 5,300 rpm Largest Gain: 23 ft-lbs @ 3,600 rpm

The torque curve shows what might be considered typical of a sizable change in cam duration. Stepping up 8 degrees in cam duration and increasing the LSA by 6 degrees (from 113 to 119) enhanced top-end power production. There was a trade-off in torque production below 4,700 rpm because the milder (NA) cam offered better power down low.

Test 5: Effect of LSA on a Supercharged LSX

Does the LSA affect the boost and power curves of a supercharged LS3? Obviously the answer is yes or this would be one very short test. Typically blower cams (such as the factory LSA and LS9 cams) are ground with very wide LSAs. Those factory cams featured 121.5-degree LSAs, but it is not uncommon for blower cams to be in the 119- to 120-degree area. In comparison, typical performance cams for LS3 applications are slightly tighter, in the 112- to 114-degree range.

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This begs two questions: What happens if you just run your blower engine with a cam that you know works well on an NA LS3? Will a powerful LS3 cam work well once you add a supercharger?

To answer these questions, I set up a test on the GM B15 LSX engine. Equipped with a Whipple supercharger, I wanted to test two cams with distinctly different LSAs. The two cams (one from Comp and the other from BTR) were as close as possible in specs other than the LSA. The tight LSA cam from Comp had a .617/.624-inch lift split, 231/247-degree duration split, and 113-degree LSA. The BTR blower cam had a .617/.596-inch lift split, 231/248-degree duration split, and wider, 120-degree LSA.

Equipped with the 113-degree cam, the blower engine produced 758 hp and 681 ft-lbs of torque. Replacing the 113-degree cam with the BTR cam increased the power output slightly to 768 hp and 679 ft-lbs of torque. The blower cam offered slightly more power at the top of the rev range, but the tighter LSA cam offered more low-speed torque.

An average (tight LSA) street cam works well, even on a blower engine, but is there extra power to be had from a wider LSA?

Tuning is critical on any LS3 application, but it’s super critical on a supercharged combination. I employed a FAST management system to dial in each combination, but the air/fuel and timing curves were identical for each cam.

Effect of LSA on a Supercharged LSX (Horsepower)

113-Degree LSA Cam: 758 hp @ 6,200 rpm 120-Degree LSA Cam: 768 hp @ 6,200 rpm Largest Gain: 10 hp @ 6,200 rpm

The wider LSA (typical of a positive displacement blower cam) improved power production above 5,400 rpm but offered a slight bump at 5,000 rpm as well. Down low, the wide LSA lost power to the tighter LSA, but low-speed power is usually not a problem with the immediate boost response offered by a positive displacement supercharger.

Effect of LSA on a Supercharged LSX (Torque)

113-Degree LSA Cam: 681 ft-lbs @ 4,200 rpm 120-Degree LSA Cam: 683 ft-lbs @ 4,300 rpm Largest Gain: 19 ft-lbs @ 3,200 rpm

The 113-degree LSA cam increased torque very low in the rev range. From 3,200 to 3,900 rpm, the narrow LSA offered more low-speed torque, but lost out in terms of peak power to the wide LSA. The question now is, Where do you want your extra power?

Test 6: Effect of LSA on a Stroker LS3

To find out how LSA affects the power curve on NA engines, I had Crane grind me a pair of cams with identical lift and duration values but altered LSAs. Both cams featured .624-inch lift (intake and exhaust) and 232/242-degree duration splits, but one cam featured a tight 108-degree LSA, while the other came in at 120 degrees. This obviously altered the cam timing events, but the test on LSA is interesting nonetheless.

The 402 stroker test engine was actually a hybrid of sorts, featuring an LS2 block and LS3 heads. The aluminum block was treated to a 4.0-inch stroker crank from Speedmaster, along with Carrillo rods and CP (flat-top) pistons. Topping off the hybrid stroker was a set of CNC-ported Chevy Performance L92 heads. Offering a tad more than 350 cfm, the heads flowed more than enough to support the intended power level for the test. The stroker also featured a FAST LSXR LS3 intake, Big Mouth throttle body, and 17 ⁄8-inch Kooks headers.

The idea was to run the pair of cams to illustrate the power differences (if any) offered by the change in LSA. Equipped with the 120-degree cam, the stroker produced 570 hp at 6,200 rpm and 535 ft-lbs of torque at 5,200 rpm. After swapping to the 108-degree cam, the peak numbers stood at 572 hp at 6,300 rpm and 543 ft-lbs of torque at 5,100 rpm. A difference in 2 hp is not significant, but the real change came elsewhere in the curve.

The tighter LSA dramatically increased power production lower in the rev range. The cam swap netted an additional 36 ft-lbs of torque down low, but the additional torque gains continued through the rev range. Only for a short 150-rpm stint did the two cams produce the same power. The one downside to the tight (108-degree) LSA cam was idle quality because the idle vacuum was down significantly compared to the 120-degree cam.

JE supplied a set of asymmetrical, flat-top pistons for the 402 stroker.

The test engine was a 402-inch stroker LS2 block equipped with LS3 heads. The short-block included a 4340 Scat crank and 6.125-inch rods.

Effect of LSA on a Stroker LS3 (Horsepower)

120-Degree LSA Cam: 570 hp @ 6,200 rpm 108-Degree LSA Cam: 572 hp @ 6,300 rpm Largest Gain: 10 hp @ 6,500 rpm

In terms of horsepower production, the tight 108-degree LSA cam offered more power everywhere. The 120-degree cam was able to equal the 108-degree cam for 200 rpm (from 6,000 to 6,200), but lost out everywhere else. I expected the 120-degree cam to come on strong at the top of the rev range, but on this stroker, the 108-degree was the better choice.

Effect of LSA on a Stroker LS3 (Torque)

120-Degree LSA Cam: 535 ft-lbs @ 5,200 rpm 108-Degree LSA Cam: 543 ft-lbs @ 5,100 rpm Largest Gain: 36 ft-lbs @ 3,700 rpm

It is obvious from the torque curves that the tighter 108-degree LSA cam offered considerably more torque down low and through most of the curve. I saw this same scenario on the test with the supercharged application, although I did not try a 108-degree LSA on that engine. The downside to the tight LSA cam was idle quality, but if you are after power, the 108 was definitely the way to go.

Test 7: Carb vs EFI Cam on a 417 LS3 Stroker

This test was interesting in that it came about after hearing a heated discussion online about the merits of cams designed specifically for carbureted LS applications. In truth, the carbureted cam design has less to do with what supplies the fuel than does the intake manifold design. Carbureted cams are generally designed for short-runner, single-plane manifolds rather than a specific carburetor. That enthusiasts even use the terms “carbureted” and “EFI cams” is reason enough to schedule a test.

As this and other tests revealed, the optimum cam for a given application works well with both forms of induction. By this I mean that if a cam offers more power in carbureted form, it will do so if you switch over to fuel injection.

The test engine for this comparison was a 417 stroker built from an LS3 aluminum block. Included were a 4.0-inch Scat crank, K1 6.125-inch rods, and JE forged pistons (with Total Seal rings). Topping the stroker was a set of GM Performance CNC L92 heads from Gandrud Chevrolet. The carbureted combination was run with an Edelbrock Victor Jr. intake and Holley 950 Ultra XP carburetor; the EFI combo included a FAST LSXR intake, Big Mouth throttle body, and 75-pound injectors.

In the carbureted corner was a Comp grind that offered a .623/.596-inch lift split, 247/258-degree duration split, and 110-degree LSA. The EFI cam was slightly milder with a .620/.596-inch lift split, 239/250-degree duration split, and wider 113-degree LSA. The graphs reveal that when tested with both the carbureted and EFI induction systems, the “carb” cam consistently offered more power. Neither the carb nor the EFI favored one of the cams; the carb cam was right for the application regardless of the induction system.

What cam works better, one designed for a carbureted application or one for an EFI application?

In addition to running both cams with an Edelbrock (carbureted) intake and Holley carb, I also ran the two cams with a long-runner, FAST EFI intake.

Carb vs EFI Cam on a 417 LS3 Stroker (Horsepower)

Carb Cam (carb combo): 628 hp @ 6,700 rpm EFI Cam (carb combo): 611 hp @ 6,700 rpm Largest Gain: 17 hp @ 6,700 rpm

In this comparison, I tested a pair of cams designed for carbureted and EFI applications. The carb cam was slightly wilder in specs and offered a tighter LSA. Run on a carbureted stroker, the carb cam offered more power above 5,300 rpm and below 4,700 rpm, but the two combinations yielded near identical torque values. Given the longer duration, I expected the carb cam to trade power down low to the EFI cam, but such was not the case.

Carb vs EFI Cam on a 417 LS3 Stroker (Torque)

Carb Cam (EFI combo): 604 hp @ 6,400 rpm EFI Cam (EFI combo): 585 hp @ 6,400 rpm Largest Gain: 20 hp @ 6,500 rpm

I tested the carb versus EFI cam once again on the same stroker combination, but this time it was equipped with a long-runner, EFI manifold. Once again, the carb cam offered more power above 5,300 rpm. The two produced identical low-speed power (which surprised me), but the EFI cam offered slightly more power from 4,500 to 4,900 rpm.

Written by Richard Holdener and republished with permission of CarTech Inc

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