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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The LS engine platform is versatile; as such, you have your choice of carburetion, central fuel injection, or multi-port injection. It all depends on the application and performance goals. The advantages of running a carburetor include lower cost and a more simplified system. Central injection, also called throttle body injection (TBI), involves running a carb-style intake manifold with a throttle body that features built-in injectors. Multi-port injection provides a “factory” approach, utilizing an air throttle body with an injector dedicated per cylinder, injecting fuel into each intake runner.

The MSD LS ignition controller kit includes everything needed for installation except of a pair of coil harnesses, which can be purchased from any Chevy dealer (or you can use the coil harness that originally came with your engine). Three versions of controller are available: one for a 24-tooth reluctor, one for a 58-tooth reluctor, or a new version that will work with either reluctor tooth count.

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Running a carbureted LS engine is extremely simple and requires no modifications. The fuel system requires no electronic management. Simply bolt on a carb-style intake manifold and carburetor. For ignition, you’ll need an ignition controller, a set of eight coil packs, and the harness to connect the controller and coils. MSD, for example, offers a 6LS ignition controller for either 24-tooth reluctors or a 6LS2 controller for 58-tooth crankshaft reluctors. The MSD harness connects the controller to the coils, the cam position sensor, and the crank position sensor. No programming is needed. The ignition controller includes a set of preprogrammed plug-in “chips,” each with its own ignition curve. Or, you can create a custom curve using the included CD and a laptop or desktop computer. For those who prefer the appearance, simplicity, and lower cost of a carb setup, this is the easiest and least expensive approach. ECU is not needed; only the small ignition controller is required. MSD also recently introduced an LS ignition controller that accommodates either reluctor wheel tooth count.

Changing the ignition curve on the MSD controller is as simple as plugging in a different chip. Each chip is numbered. The instruction manual provides the ignition curve that each chip offers.

For those who prefer fuel injection, the next level involves TBI, which is often referred to as a “wet”-style throttle body. Using a carb-style intake manifold, an injection-equipped throttle body mounts like a carburetor. This wet-style throttle body handles both air and fuel in one package, distributing the mixture from the central location above the manifold runners. The throttle body features built-in fuel injectors and somewhat resembles a 4-barrel carb in appearance. A built-in throttle position sensor is featured as well. A kit includes the appropriate wiring harness and a controller, which can be programmed or, depending on the make and model, run as-is, with a self-learning program that adjusts fuel and spark as you drive. Toss in a set of eight coil packs, and you’re ready to go.

Be aware that depending on the aftermarket kit you purchase, you may need to also obtain a pair of coil pack harnesses. These are readily available from a GM dealer.

Another option is to use a carb-style intake manifold, an air throttle body, and eight individual fuel injectors that are placed in bungs at the base of each intake runner. This provides a carb-style air intake coupled with direct-port fuel injection. Again, since we need to control both fuel and spark, a controller and wiring harness are required in addition to the coil packs. These systems may be obtained as individual components or as a complete kit. Multi-port fuel injection intake manifolds are also available for mounting the air throttle body up front, referred to as “longitudinal” intake manifolds.

The final option is a factory-style crossover intake manifold that resembles the OEM system in terms of overall appearance and design.

Either a factory or aftermarket ECU is required to control both fuel and spark. While respectable horsepower and reliability may be obtained with any of these approaches, fuel injection offers a more precise approach that is less susceptible to temperature, humidity, and altitude issues, but those who are adept at carburetor tuning may feel more comfortable with a carb setup. As an example, my shop has built a number of carb-equipped and TBI-equipped LS engines, producing from 625 to more than 670 hp. Your choice will depend on budget, preferred appearance, and application. Manufacturers such as Holley, Edelbrock, and others offer a wide range of fuel and air delivery components and systems for Gen III and IV LS engines.

Intake Manifolds

For those who wish to run either carburetion or a central fuel injection setup, a host of intake manifolds are available through the performance aftermarket. Holley, for example, offers single-plane, dual-plane, and hi-ram intake manifolds that accept a single or dual 4-barrel carburetor setup or a central injection throttle body such as those offered by MSD, FAST, and others. Another option is to run a carb-style intake manifold that accepts an air intake throttle body, along with per-cylinder fuel injectors via injector bungs machined into the manifold runners.

Multi-port fuel injection manifolds of the longitudinal style (similar to OEM) are available in a wide range of designs by Holley, Edelbrock, FAST, and others. These involve a large plenum with either high- or low-profile designs, accepting a front-mounted throttle body. This style is ideal for those who want to upgrade their existing factory manifolds.

Dart Machinery, a long-time major player in the development of high-performance and racing LS blocks and cylinder heads, now offers two intake manifolds for the LS platform for those wishing to run either carburetors or central throttle bodies. A 10-degree Box Ram intake features tall runners and a billet pent-roof top plate. Another version features a single 4150-style carb or throttle body flange.

Our Holley single-plane intake manifold PN 300-132BK features a black ceramic coating and cathedral ports (LS1/LS6/LS2 style) and is designed for an optimum operating range of 2,500 to 7,000 rpm. Ports measure 2.66 inches high x .92 inch wide. The 4150-style square-bore flange accepts up to 1.75-inch-diameter throttle bores, and the height from the valley plate to the carb flange is 4.95 inches.

The Holley Hi-Ram intake PN 300-226 offers a modular design, allowing a single- or dual-carb setup, with a top plenum box available for either approach.

Either manifold is available with or without injector bungs. The extra-tall/ long runners provide higher horsepower and an extended RPM range.

Dual-carburetor plenum PN 300-216 is shown here. The plenum bolts to the manifold and is sealed with an O-ring strip.

In addition to square-bore manifolds for LS cathedral-port heads, Holley also offers a single-plane intake with LS3-style rectangular ports as well as with LS7 ports.

Throttle Body Injection

As mentioned earlier, throttle body injection (TBI) involves a throttle body with built-in fuel injectors in one neat package. Examples include Holley’s Terminator EFI and new Sniper EFI, FAST’s EZ-EFI, Edelbrock’s E-Street and Pro-Flow 3, and MSD’s Atomic EFI. For those who wish to obtain a simple-to-install electronic fuel injection atop a 4-barrel intake manifold, these systems are the perfect solution. The all-in-one air/fuel unit mounts just like a carburetor, requiring minimal wiring. Fuel injectors, throttle position sensor, and ECU are built into the unit. Most are rated to handle up to about 650 hp. As one example, I’ve used Holley’s EFI Terminator on an LS build that dyno’d at 657 hp. Setup was surprisingly easy and produced a better power and torque curve than the dyno shop’s dyno-proven “known good” custom carb.

During one particular build, we fitted LS3-style Trick Flow heads and a Holley LS3-style manifold along with a Holley 850-cfm carb. Interestingly, we tried a 1-inch carb spacer and picked up another 10 hp on the dyno.

Holley’s EFI Hi-Ram longitudinal intakes are available to accept 92- to 105-mm throttle bodies. These intakes are available for either cathedral-port (LS1/LS6/ LS2) or rectangular-port LS3/ L92-style heads, with finishes in natural or ceramic black. Injector bungs are featured, to be fed with a billet fuel rail at each bank. (Photo Courtesy Holley)

A pair of Holley 600-cfm Ultra carbs are mounted “sideways” on the plenum to facilitate a throttle linkage system. This induction setup on a 408-ci LS engine equipped with Trick Flow heads pulled 670.5 hp at 6,500 rpm on the engine dyno and 581.7 ft-lbs of torque at 4,900 rpm. Perhaps not a practical street setup, but it sure looks cool and loves high RPM.

Holley’s Sniper longitudinal EFI intakes are fabricated sheet-aluminum units as opposed to cast. They are available for various throttle body sizes, in cathedral or rectangular ports, in natural, polished, or black. (Photo Courtesy Holley)

Weiand’s cross-plenum EFI intake is a cast-aluminum unit, available for cathedral-port applications. (Photo Courtesy Holley)

Among the factory and aftermarket multi-port injector manifolds available, Edelbrock now offers a very cool Cross-Ram intake specifically for LS3-style heads. This features a relatively low profile and long-runner design that accepts two 90-mm throttle bodies, making it a great choice for those who intend to run twin turbochargers. These are available with the right and left plenums in either red (PN 7141) or black (71413). (Photo Courtesy Edelbrock)

Fuel Air Spark Technology (FAST) offers an array of multi-port injection manifolds, constructed of high-strength polymer in a module design of an upper plenum and runner bottom section, allowing porting of individual runners. Selections include the LSX, designed to accept a 92-mm throttle body for cathedral-port heads, and the LSXR, designed for a 102-mm throttle body, with applications including LS1/LS6/LS2/LS3 and LS7 heads. Also offered is the LSXRT, for use with a 102-mm throttle body, for cathedral-port heads only. Previous intake manifolds featured a silver/aluminum color, while recent models have been released in an all-black finish. Depending on the model, increases of 25 to 30 hp are reported compared to stock manifolds. (Photo Courtesy FAST)

A FAST manifold and fuel rails installed in a Z06 Corvette.

Aftermarket performance wet-style throttle bodies are available in a range of cfm ratings, sometimes in the 900-cfm-or-greater range. Don’t be misled by comparing these ratings to those of carburetors. While a carburetor moves both fuel and air and must be sized according to engine displacement and horsepower, an EFI throttle body will simply make the volume of air that is needed at a specific time.

For the dual-carb setup, a pair of 600-cfm Holley Ultra carbs, PN 80801-RD, worked well on a 408-ci LS build along with a tunnel ram manifold.

The FAST composite manifolds are modular. With the top plenum removed, individual runners are accessible for custom porting.

More recent introductions include Wilson Manifolds’ new LS applications for EFI setups, including one with a flat billet top plate that allows mounting a pair of 4-barrel air throttle bodies and one with a low-profile system that accommodates a single front-mount throttle body and includes extra nitrous injection ports. All components are CNC-machined from billet-aluminum stock. Wilson is well established for providing induction systems for professional racing applications that also apply to high-performance street use.

Just because you’re dealing with an LS engine doesn’t mean you’re restricted to using fuel injection or ugly factory valve covers. You can easily achieve a radical old-school look by using your choices of carburetion setup and small-block Chevy valve covers thanks to available valve cover adapters. This Hi-Ram Holley intake manifold outfitted with dual 600-cfm Holley carbs and tall small-block Chevy valve covers is a good example. The tall velocity stacks added a nice, radical touch. This example might be appealing for street rod owners who prefer appearance over practicality, especially for those who view “too much” as “not enough.”

Edelbrock’s Pro-Flo XT LS injection system features a large plenum and tapered runners for a broad torque band. This setup reportedly provides an increase of 30 hp over a stock LS6 manifold. Applications for this manifold include LS1/LS6 and LS2. The manifold is offered in either satin or black. The management system includes everything needed for installation. (Photo Courtesy Edelbrock)

This LS7-equipped drag car built by Hutter Engineering of Chardon, Ohio, is a good example of a maximum-output naturally aspirated setup. Note the custom Wilson fabricated intake manifold and dual throttle bodies fed via separate carbon fiber intake tubes.

Dart Machinery has also developed a line of high-flowing tall-runner intake manifolds. This version is its 10-degree Box Ram manifold equipped with a billet pent-roof top plate. It is available with or without injector bungs.

If you’re running a carb setup on an LS engine, consider adding a breather directly to the front of the valley cover. This allows more efficient reduction of crankcase pressure as opposed to breathers on the valve cover(s) only. This involves boring a hole in the valley cover to allow welding an aluminum breather tube, then attaching a breather element. Position it as close to the front intake manifold runners and carb as possible while still providing enough clearance to service the breather element.

Billet-aluminum fuel injector rails commonly allow plumbing crossover hoses in –6 AN or –8 AN size. The –6 is equivalent to a 3/8-inch inside diameter; –8 is equivalent to a 1/2-inch inside diameter. Rails are also available in a variety of finishes, including polished, black, red, or blue.

Dart also offers a 4-barrel long-runner manifold for a single 4150-style carb or throttle body, also available with or without injector bungs. The tall, long runner design definitely will boost the RPM range and will increase power at higher engine speeds.

A sleek new low-profile injection manifold from Plazmaman (an Australian firm) features 100-percent billet-machined construction made of 6061 aluminum, available in port sizes to accommodate LS1, LS3, and LS7 ports. Nitrous compatibility is available with a 16-injector version and built-in burst panels. Finishes are available in clear or black anodized surfaces. Yet another offering is from Magnatron, featuring a CNC-machined lower intake and curved upper plenum, designed to accommodate any size throttle body with available adapters.

A pair of fuel injectors is featured on both the primary and secondary sides of the throttle body. Unlike other TBI units that cover the injectors, the injectors are visible and easily accessed for service to mimic the look of a carburetor.

The FAST EFI throttle body provides the appearance of a carburetor, with multiple injectors hidden behind faux fuel bowl covers. The throttle body features two harnesses, one that connects to the EFI controller and one that connects to the water temperature sensor on the left cylinder head.

The FAST EZ-EFI 2.0 kit includes everything required for fuel management. Our kit even included an inline high-pressure fuel pump and adjustable regulator. For LS applications, the FAST EZ LS ignition controller, which connects to the EFI main harness, is also required.

An example of the FAST EFI throttle body injection mounted to a Holley single-plane intake manifold. The outward appearance satisfies those who prefer a carburetor appearance, combined with the higher fuel delivery precision offered by EFI. Utilizing a TBI unit allows installation of a 4-barrel-style air cleaner. The faux “fuel bowl” covers hide the injectors from view.

The right side of the FAST throttle body features a built-in throttle position sensor.

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The FAST EZ-EFI control module. This can be installed in the vehicle interior.

The FAST EFI throttle body injection system features a handheld control module that can be temporarily connected during setup or mounted in a convenient in-car location, allowing quick and easy adjustments.

The Terminator EFI is available in Hard-Core Gray (as shown here) and in a fully polished version. The Terminator throttle body unit is compact and as easy to install as a carb, featuring two fuel fittings, one for feed and one for fuel return.

The Holley Sniper EFI features a built-in ECU (top image at left) and a built-in fuel pressure regulator (bottom). (Photo Courtesy Holley)

The Holley Terminator EFI system includes everything needed for installation. Setup is fairly easy and straightforward, once you take the time to read the setup instructions! The dark-charcoal anodized finish gives a pro appearance.

The Holley Terminator EFI features 950 cfm of potential airflow, with four integrated 65-pound fuel injectors. Don’t be intimidated by the large airflow capacity. Only enough airflow will be utilized based on the air/fuel delivery requirements at any given engine speed. The 900-cfm capacity is simply the available airflow volume.

The Terminator system includes an ECU that can easily be mounted in a vehicle interior due to the lengthy harness.

Holley’s new Sniper EFI is available in polished, black, or gold. Four injectors, a throttle position sensor, ECU, and fuel pressure regulator are all built into the bolt-on unit. These throttle body injection units are rated as handling up to 650 hp. (Photo Courtesy Holley)

EFI Alternative

Many performance enthusiasts are familiar with Borla, makers of performance exhaust systems. However, you may not be aware of that firm’s entry into the induction market. Borla Induction specializes in fuel injection systems that feature multiple downdraft and sidedraft setups that mimic the appearance of old-school downdraft or sidedraft multiple-carb systems. These assemblies are extremely cool, offering an alternative to more commonplace EFI systems. Complete system offerings include Ford FE, Ford and Chevy small-block, and more, but recently they’ve introduced setups for the LS platform. They’re pricey, but extremely exotic in appearance. The systems combine the vintage look of multiple-carb road race induction with the efficiency of electronic fuel injection. If your budget allows, you need to check this out.

Wilson Manifolds, long known for its race-application CNC and welded aluminum intakes, has released two LS manifolds. The example shown here features a CNC-machined EFI intake with a billet machined upper plenum cover that accepts a pair of billet 4150 or 4500 flange throttle bodies.

Wilson also offers an LS EFI intake manifold with central upper plenum that accepts a range of throttle body sizes and includes extra injection bungs to accommodate a nitrous system.

This hard-wired handheld controller plugs into the main harness and allows system setup, calibration, advanced tuning, on-the-fly programming, and system adjustments when located within the driver’s reach. The handheld controller may be connected at all times but is not necessary if no additional tuning is desired. You must read the instructions for installation and setup of the EFI system. Don’t try winging this. The instructions for setup are lengthy but very easy to follow. Don’t be intimidated by the length of the instructions. If you take the time to read, setup will be a breeze. The controller’s main menu offers selections for gauges (a graphic view of various sensor readings), monitor (numeric views of sensor readings), wizard (creates base calibration and performs TPS setting), tuning (for adjustment of various parameters), and file (allowing you to load and save numerous calibration settings). The amount of information available on the controller is amazing.

MSD Atomic TBI is designed to support up to 625 hp when used with the specified high output fuel pump. (Photo Courtesy MSD)

Throttle Body Size

When upgrading to a larger throttle body on a multi-port EFI engine, what size air throttle body is best? It depends on the anticipated engine speed at the engine’s peak horsepower. A smaller throttle body increases air velocity, and a larger throttle body slows air velocity. Stock LS1/LS6 engines were equipped with three-bolt 75-mm throttle bodies, while LS2 and LS3 engines featured four-bolt 90-mm throttle bodies. Popular aftermarket throttle body sizes range from 90 mm to 105 mm in size, with 90 mm to 95 mm applicable to modified street and street/strip applications. The 105-mm throttle bodies are designed for maximum airflow in wide-open throttle (WOT) applications, such as drag racing.

The MSD Atomic EFI features the following:1. Internal fuel rail that feeds all four injectors. 2. ECU integrated into the throttle body, reducing wiring. TPS (throttle position sensor), MAP (manifold absolute pressure) sensor, IAT (intake air temperature) sensor, and fuel pressure sensors incorporated into the ECU. The only sensors needed for connection are the coolant temperature and wide-band oxygen sensors, which are included in the kit. 3. Fuel delivery handled by four 80-pound injectors. 4. An automatic, self-calibrating, noncontact sensor TPS, so no setup configuration is needed. 5. A throttle body that bolts in place of a standard square bore carburetor and accepts most common throttle and kickdown linkages. (Photo Courtesy MSD)

An Australian company, Plazmaman, has recently released a series of CNC–billet-machined 6061 aluminum low-profile intakes for the LS platform that accept either OEM or aftermarket throttle bodies. The sleek profile and incredibly detailed exterior finish appear to be easy to clean, and this model is offered in either a silver/clear or black “stealth” anodized finish. It is available with 8 or 16 injector ports (added ports for those who plan to add nitrous injection) for LS1, LS3, and LS7 port applications.

Fuel Injector Size

Follow this handy formula to calculate the optimum injector size for your application: (Max HP x BSFC) /  (Number of Injectors x Duty Cycle) =  Injector Size in Pounds Per Hour

Brake-specific fuel consumption (BSFC) represents the amount of fuel consumed per unit of power produced. BSFC can be found by engine dyno testing, or you can follow these generic guidelines:

• For a high-compression engine of approximately 10.5:1 or higher, running on gasoline, BSFC is about .45 for a stock or moderate build, and about .55 for a highly modified engine.
• For a modified forced-induction engine (supercharged or turbocharged), BSFC is about .55 to .65.

Duty cycle represents the amount of time that a fuel injector is open versus the total time between cylinder firing events. A safe duty cycle for a stock or mild engine is .80, and .85 for modified engines.

Aftermarket throttle bodies are available in a variety of sizes and offer smooth, radiused air inlets and precision-fit blades. For the appearance-minded, they’re also offered in various finishes. (Photo Courtesy Holley)

Dry-style throttle bodies are available in machined aluminum in various anodized color finishes.

As an example, let’s say you plan to obtain about 600 hp with a naturally aspirated gasoline engine that has been highly modified. In this example, we’ll use a BSFC of .55 and a duty cycle of .85. (600 hp x .55 BSFC) /  (8 Injectors x .85 Duty Cycle)

So, 330 / 6.8 = 48.5 pounds per hour. As another example involving moderate modifications, where we anticipate 500 hp, we’ll use a BSFC of .45 and a duty cycle of .80. (500 hp x .45 BSFC) / (8 Injectors x .80 Duty Cycle) 225 / 6.4 = 35.156 pounds per hour

The above examples determine injector flow rating as a starting point. To finely tune the system, an adjustable fuel pressure regulator can be used to modify the flow rating. By noting the fuel injector’s static flow rating at a specific fuel pressure, you can calculate a change in injector flow rate by altering pressure. Injector manufacturers will be able to provide an injector’s static flow at a specific level of fuel pressure. For example, an injector may be rated at 39 pounds per hour at 40 psi. By increasing fuel pressure, the injector flow rating can be increased.

The formula for determining an increase in flow based on an increase in fuel pressure is as follows:

(Square Root of New Pressure / Old Pressure) x Old Flow Rating

As an example, an injector has a published pressure of 35 psi and a static flow rating of 39 pounds per hour but we want to see how an increase to 42 psi of fuel pressure will affect the flow rating.

42 (New Pressure) / 35 (Old Pressure) = 1.2 The square root of 1.2 = 1.0954451150103321 1.0954451150103321 x 39 (Old Flow Rating) = 42.7 pounds per hour In this example, we can see that by boosting fuel pressure from 35 psi to 42 psi, we can change the flow rating from 39 pounds per hour to 42.7 pounds per hour.

Note that fuel injectors require higher fuel pressures than do carburetors. While a carburetor requires pressure in the range of 4 to 6 psi, depending on the application, fuel injectors may require 35 to 70 psi. Obtaining the optimum-size injector is a balancing act involving both the flow rating and the fuel pressure.

Fuel injectors are electronically controlled valves that spray fuel into the combustion mix on demand.

Low Impedance versus High Impedance

High-impedance resistance injectors (about 10 to 16 ohms) and low-impedance resistance injectors (about 1.5 to 4 ohms) are available. Which type do you need? If you’re running an OEM ECU (computer), generally you need high-impedance injectors. These feature a somewhat slower response time. If you’re running a performance aftermarket ECU, you need low-impedance injectors, which react more quickly. If you run low-impedance injectors with an OEM computer, you run the risk of damaging the OEM ECU. Most injectors that feature high flow rates are low-impedance type. Low-impedance injectors offer a faster opening response time, generate less heat, and are generally preferred for aftermarket performance systems, although this can vary depending on the specific aftermarket system.

Choosing the Correct Injector Size

If you buy a complete system kit, the injectors are likely included. If you need to determine your own injector requirements, you can target the appropriate-size injector based on your engine’s anticipated horsepower and the engine’s brake specific fuel consumption (BSFC) efficiency number. BSFC represents the amount of fuel that the engine will consume, divided by its power output (how many pounds of fuel will be used per horsepower produced in a hour).

Commonly used fuel injectors include the EV1 and EV6 body styles. The EV1 is the “fat” style, often generically called the “Ford” style. The EV6 features a skinnier profile and a different connector (such as the EV6-style injectors used in newer Fords and GM LS engines). The thinner-profile EV6 also is available in different lengths, so between lower O-ring diameter and overall length differences, you can really get confused if you’re piecing an MPFI system together without knowing what you’re doing. For that very reason, it’s best to simply purchase a complete system, where the injectors (in addition to impedance and flow rate) are already matched to fit your intake manifold, fuel rail, and harness setup.

Aftermarket performance systems require a fuel injection controller, or ECU, a throttle position sensor, and an oxygen sensor. Depending on the system, sensor requirements may include a knock sensor, intake air temperature sensor, MAP sensor, and coolant temperature sensor. If the engine was originally equipped with a fuel-injection system, the ignition system will already be controlled by an ECM and will likely incorporate cam and crank position sensors. If the engine was originally equipped with a distributor, EFI systems are available that take this into account, providing fuel injector control. Instead of piecing a system together, it’s best to purchase a coordinated system that includes the throttle body along with all necessary control accessories.

Pictured here are EV1 (left) and EV6 styles. Both styles are available in either low or high impedance.

Harness connector styles. At left is the Minitimer style. At right is the USCAR style. Note that the Mimitimer connector features a rectangular housing and flat-blade terminals, while the USCAR style features a square housing and pin-style terminals.

Written byMike Mavrigian and republished with permission of CarTech Inc

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The LS engine family began with what GM refers to as the Gen III engine platform, which included the LS1 and LS6. The Gen IV family began with the LS2 and includes LS7, LS3, LS9, and L92. Although the LS2 engine shared the cathedral intake port head design that carried over from the earlier LS engines, the LS2 falls under the Gen IV category basically because the camshaft timing sensor moved to the front of the block, whereas earlier blocks featured the cam sensor at the rear. This is the only reason the LS2 is referred to as a Gen IV engine.

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All Gen IV LS engines feature a front-mounted cam position sensor (mounted to the front timing cover), with cam timing picked up by reluctor blocks on the camshaft gear.

LS2 Differences

The primary differences between the LS2 and other Gen IV engines involve increased displacement and cylinder head design. The LS2 offers 6.0L of displacement while the LS3 and LS9 feature 6.2L, with the LS7 providing 7.0L of displacement.

Of the various differences in cylinder head design, the most notable involve the intake ports. The LS2 heads feature the tall cathedral ports (similar to the intake ports found on LS1 and LS6), while the LS7, LS3, and LS9 heads feature a rectangular intake port design (often referred to as square ports, although they are actually rectangular).

This ready-to-install LS aftermarket crate engine featuring LS3 heads is available in horsepower ranging from 540 to 660. Thanks to LS cylinder head design and the appropriate cam profile, such horsepower numbers have become commonplace.

This LS7 engine is being fitted to a 1969 Camaro. While creative turbo plumbing was required during fabrication and test fitting, engine and transmission installation was relatively straightforward thanks to readily available LS-swap mounts.

Performance Gains

The performance automotive aftermarket’s prompt and enthusiastic support for the LS platform made horsepower gains possible through wide-ranging development and by offering stronger forged crankshafts, varying crankshaft strokes, stronger forged connecting rods in lengths suitable for varying stroker combinations, and forged-aluminum pistons in a wide range of bore diameters, compression heights, and dome volumes. Roller camshaft profiles are available from all leading aftermarket cam makers to suit any desired build in terms of horsepower, torque requirements, and power bands. To provide much more durable threaded fasteners for the LS, stronger billet-steel main caps, cylinder head bolts or studs, main cap bolts or studs, and rod bolts are offered, all designed for torque-value installation, eliminating the need for torque-plus-angle tightening.

It’s become rather commonplace for dual-turbo LS engines to produce well beyond 1,000 hp.

Aftermarket forged-aluminum pistons are offered for LS applications in a full range of diameters, compression heights, and dome volumes and configurations to suit any conceivable requirement.

The majority of LS factory engines feature powdered metal main caps. While suitable for street and some racing applications, a move to steel-billet main caps provides added bottom-end strength. Aftermarket blocks are commonly available with either ductile-iron or steel-billet caps.

Some factory LS engines, such as the LS7, are already fitted with steel-billet main caps. These OEM four-bolt main caps provide the strength to support more than 500 hp and 481 ft-lbs of torque.

LS cylinder heads are critical power makers due to their superior flow. Aftermarket head manufacturers have developed and refined the LS designs for even better flow by means of cathedral or rectangular intake ports and a wide range of valve sizes and combustion chamber volumes.

Based on the original GM LS cylinder head designs, sophisticated aftermarket cylinder head innovations have been developed that boost power well beyond that offered by the factory heads. Choices include Gen III and LS2 cathedral-port heads and Gen IV rectangular-port heads, with intake volumes ranging from about 225 cc to more than 255 cc, along with premium stainless-steel valves and improved flow designs for both straight and offset intake rocker applications and fully CNC-machined ports and chambers. The primary “secret” of LS power lies in the cylinder head designs. While factory heads such as the L92 style are excellent platforms, the aftermarket has really stepped up to provide power well beyond the OEM offerings.

Aftermarket forged cranks provide added strength and are available in a variety of strokes. Both standard and super-lightweight versions are offered, covering the needs of both street and extreme racing applications.

OEM rocker arms perform well, but aftermarket performance full-roller rockers enhance performance and durability with forged-aluminum bodies, hardened pushrod cups, heavy-duty caged trunnion bearings, and roller bearing valve tips. In comparison, the factory powdered metal rockers, which feature roller bearing trunnions, have frictional contact with valve stem tips. Aftermarket full-roller rockers are better able to withstand high engine speeds and higher cam lifts while offering reduced friction due to the roller bearing contact at the valves. Aftermarket rockers are also readily available in both a standard 1.72:1 ratio and a 1.8:1 ratio.

If you plan to reuse the factory rockers, you must upgrade to aftermarket fully caged bearing trunnions; factory uncaged bearings can dislodge.

Aftermarket full-roller rocker arms offer superior strength and reduced friction because roller bearings contact the valves instead of the OEM frictional contact design. Aftermarket performance roller rockers are available in both 1.72:1 and 1.8:1 ratios.

The aftermarket has stepped up to offer both iron and aluminum LS blocks that provide more latitude in overboring and stroking, in addition to enhancements that provide superior oiling, cooling, and, most important, strength.

The LS builder is no longer limited to the factory plastic lifter guide trays. Also available are tie-bar link lifters that provide superior precision by keeping lifter rollers in plane with the cam lobes. High-quality aftermarket lifters also offer superior strength for higher valve spring pressures and to accommodate higher engine RPM.

Retrofitting the LS

While factory lifters are individual and are guided within plastic guide trays, aftermarket choices now include lifters that retrofit to these plastic guides and link-bar-paired roller lifters that eliminate the plastic guides. In basic terms, the aftermarket fulfills the requirements of performance and racing applications by addressing the various weak points of the factory designs both to boost power and to provide a much higher level of durability for high-stress application environments.

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A full range of additional components is readily available to increase power and durability, including viscous-dampened crankshaft balancers, improved-flow mechanical and electric water pumps, and enhanced-design timing covers that provide additional timing chain clearance and allow cam timing changes without the need to remove the crank pulley. Improved oil pan designs are now available that provide added capacity and reduce windage concerns. Also offered are more-robust and powerful ignition coils, taller valve covers that provide clearance for aftermarket rockers, adapters that permit installation of Gen I small-block Chevy valve covers, a variety of intake manifolds for both injected and carbureted applications, and easy conversions to allow the use of carburetors on LS engines. Forced induction systems are also readily available, including both supercharged and turbocharged applications.

Electric water pumps are popular among many builders and are now available for LS applications. Depending on your belt routing requirements, these pumps are offered with or without an idler pulley.

For those who wish to run their LS engines carbureted, a variety of intake manifolds are available in dual-plane, single-plane, low- and tall-profile, and single- or multiple-carb designs. These manifolds are also offered without injector bungs or with injector bungs for those who wish to run a central-mounted throttle body with per-cylinder injectors.

Unlike the early days when the LS platform was considered the “new and unique” performance engine, thanks to the performance aftermarket we now have total coverage in performance upgrades; that is, for every single component involved in a build. Regardless of your goal, whether that involves a mild street upgrade or full-blown competition in any form of racing, including drags, road racing, oval track, etc., if you’ve got the money, the aftermarket can feed your addiction.

Aftermarket high-performance ignition coils offer superior output, reliability, and appearance over factory coils.

Example of a custom-built LSX LS7 street/competition engine featuring a FAST intake manifold. (Photo Courtesy Livernois Engines.

Although factory blocks can handle minor to major power enhancements, aftermarket blocks in both cast iron and aluminum offered by manufacturers such as Dart, Racing Head Service (RHS), and World Products provide notable improvements and versatility. Aftermarket blocks allow builders to obtain larger cylinder bore diameters and accept longer crank strokes, along with vastly improved strength and durability, giving engine builders much greater latitude in achieving more power, torque, and reliability. Thanks to support from the performance aftermarket, achieving naturally aspirated 600-plus hp is extremely easy, with forced-induction builds reaching 1,000hp and beyond.

Factory connecting rods on most LS engines are powdered metal construction. The factory rods are suitable for power up to around 450 hp or so, but it is strongly recommended to swap to forged-steel aftermarket rods, which are available in various center-to-center lengths to accommodate standard or stroker applications.

Upgrading critical fasteners in cylinder head, main cap, and rod bolt applications is essential for any high-horsepower build. Not only do quality aftermarket fasteners provide superior tensile strength, they are specified to use a torque value only, an easier installation than the factory torque-plus-angle tightening method. Unlike factory fasteners that are torque-yield one time use, quality performance aftermarket fasteners may be reused, obviously based on condition.

Because of the increased popularity of the LS platform, more and more restoration builders choose LS transplants for older muscle car applications, spawning a range of engine swap kits. Components developed to ease installation of the LS engine into older vehicles include motor mounts, frame adapters, plug-and-play controller systems for factory-type injection applications, exhaust systems that allow LS engine adaptations into a variety of popular muscle car and vintage vehicles. Essentially, all the types of power-adding and increased-durability components developed over the decades for Gen I engines are now available for the LS platform, making it the most popular standard for Chevy performance applications today.

Instead of using the factory crankshaft pulley, aftermarket balancers are available with or without grooved pulleys. The viscous-dampened balancers provide additional reduction of harmonics. These are available for either unkeyed factory-type crank snouts or keyed for aftermarket cranks.

Written by Mike Mavrigian 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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