With a stout short-block filled with an all-forged rotating assembly, the remainder of a boost-ready engine assembly includes the cylinder heads and crucially important camshaft. All LS engines benefit from excellent cylinder-head airflow—some more than others—but it is the camshaft that is the key not only to optimal power but drivability characteristics.
This tech tip is from the full book, HOW TO SUPERCHARGE & TURBOCHARGE GM LS-SERIES ENGINES.
For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE
SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://www.lsenginediy.com/how-to-build-an-ls-engine-heads-cam-and-induction/
There is an almost endless list of possibilities when it comes to boost-friendly cylinder heads for LS engines. The excellent port design and large-capacity runners allow for easy and efficient cylinder filling. Ensuring intake manifold compatibility with the heads’ intake ports is the only major caveat when selecting them for a supercharged or turbocharged combination.
Cylinder Heads
There isn’t sufficient room in this chapter to describe all of the cylinder head choices available to the LS engine builder—and more seem to arrive every month. The use of heads with six bolts per cylinder isn’t an absolute requirement on an engine making less than 1,000 hp or less than about 15 pounds of boost, but they should be strongly considered for racing applications generating high boost and high horsepower.
The other crucial detail only applies to the installation of supercharger systems that mount the compressor in place of the intake manifold. For these applications, the cylinder-head intake ports must be compatible with the intake ports of the supercharger manifold’s ports. Mostly, that means the difference between LS1/LS6/LS2-style cathedral-port heads and later-style rectangular-port heads. In fact, even the later heads don’t all have matching port shapes—the LS7 head ports have a more square design, while the LS3/L92-style ports are taller and narrower.
Also, because of the comparatively small bores of LS1 and LS6 engines (3.89 inches), when compared with the later 6.0-liter and larger engines, they can only use LS1, LS6, and LS2 heads. Using the heads of 6.2-liter and larger engines causes valve-to-block interference. However, the larger 4.00-inch bore of the LS2 enables it to use LS1/LS6 heads, as well as L92-style heads (including LS3, LS9, and LSA engines). The 6.2-liter engines (LS3, L92, etc.) can use any head except the LS7 and C5R, while the 7.0-liter LS7 and C5R blocks can use any LS-series head. The C5R head is not recommended, as it is an expensive part with a unique intake port design that requires a custom intake manifold, as well as a small combustion chamber that promotes a high compression ratio that’s incompatible with forced induction. The LS2, LS3/L92, and LS7 heads use production intakes, offer greater port volume and larger combustion chambers that are desirable with forced induction.
In general terms, higher-flow cylinder heads make the same horsepower with lower-boost pressure than a comparable engine combination with lower-flowing heads. Put another way, the boost of the supercharger or turbocharger overcomes the relative inadequacies of “smaller” heads, as the boost pressure fills the ports, and then some. That’s not to say the cylinder head isn’t important, but for most street/strip applications, the already high-flow characteristics of factory LS heads perform more than adequately with forced induction.
Later-style rectangular-port heads (whether LS7- or LS3/L92-style) are larger and have greater airflow attributes than cathedral-port heads. They are well suited to forced induction, but the ultimate selection may be influenced by bolt-on Roots/ Lysholm-type supercharger systems, because not all supercharger intakes are currently compatible with all cylinder-head port designs.
When it comes to combustion chamber design, the factory configuration is adequate, and conventional porting/blending provides a modest benefit. More crucial, however, is chamber volume, as it contributes to the engine compression ratio. A larger chamber volume lowers the compression ratio, while a smaller volume raises it. A good rule of thumb is somewhere in the 64- to 68-cc range.
Another consideration for engines projected to generate more than 15 pounds of boost is the use of cylinder heads with six head bolts per cylinder, rather than the factory-style four bolts per cylinder. When used with the appropriate cylinder block (see Chapter 8), the additional clamping power—at least 50 percent greater— of the six-bolt heads does much to prevent head-gasket failure. GM Performance Parts and Trick Flow offer six-bolt heads that fit the LSX cylinder block, although the Trick Flow heads are only available in LS1/ LS6/LS2-style cathedral-port styles. World Products also offers a six-bolt head, but it doesn’t match the bolt pattern of the LSX block, meaning it must be used with the company’s complementing six-bolt capable Warhawk cylinder block.
The LS1/LS6/LS2-style cathedral-port cylinder head (seen here) doesn’t offer the maximum flow characteristics of later heads that are based on the rectangular port design of the LS7 engine, but they are adept at generating excellent torque. With minor adaptations, later heads can be swapped on LS1/LS6 engines to maximize the airflow offered by the power adder. Also, 6.0-liter engines can use 6.2-liter L92/LS3-style heads to great effect, but again, they must be matched with the correct intake manifold. A 6.0-liter intake, for example, doesn’t fit LS3 heads; and the LS7 intake fits only LS7 heads.
GM Performance Parts offers a range of LSX six-bolt cylinder heads with LS3/L92- and LS7- style rectangular ports, as well as an LSX-DR (drag race) head that offers raised runners, an 11-degree valve angle, and a design the requires shaft-mounted rocker arms. Taking advantage of the six-bolt clamping power, however, requires they be used with LSX or RHS six-bolt cylinder blocks. The standard LSX heads use standard LS intake manifolds, while the LSX-DR requires a unique, carburetor style manifold (PN 19166954) that can be adapted for use with racing oriented turbo and centrifugal supercharger systems.
When it comes to other aftermarket cylinder heads, they are of the standard, four-bolt style. There are numerous choices, although most are based on the cathedral-port LS1/LS6/LS2-type head. They make great, higher-flowing choices for the 5.7- and 6.0-liter engines, but GM’s production and performance heads from GM Performance Parts are currently the best options for the larger displacement engines that use rectangular-port heads. Here are some of the available aftermarket heads:
- AFR (Air Flow Research) offers “Mongoose” CNC-ported cathedral-port heads in 205-cc (66- or 76-cc chambers) and 225-cc (62-, 65-, or 72-cc chambers) intake runner sizes.
- Edelbrock’s cathedral-port heads are CNC-ported by Lingenfelter Performance Engineering and feature 202-cc intake runners and 65-cc combustion chambers.
- Pro-Filer cathedral-port heads are offered in 215- and 235-cc intake runner sizes, with 62-cc combustion chambers..
- Trick Flow offers a number of cathedral-port heads, including some with a six-bolt configuration that fit GM Performance Parts’ LSX cylinder block.
An aftermarket alternative to GM heads is World Products’ Warhawk cylinder heads, offered in LS1X and LS7X styles. Each has a six-bolt design that corresponds with World’s Warhawk cylinder block, but can be bolted to a GM block using the standard four-bolt pattern. The LS1X features cathedral ports, a 15-degree valve angle, 235-cc intake runners, 2.080/1.600-inch valves, and is available with 64- or 72-cc combustion chambers. The LS7X head has rectangular ports, a 12-degree valve angle, 285-cc runners, 2.250/1.625-inch valves, and 64- or 72-cc chambers. On either head, selecting the smaller chamber volume will promote a higher compression ratio, so it must be matched with an appropriate dished piston design to keep the compression around 9.0:1 and 9.5:1 (or lower).
Perhaps the ultimate in strength and durability for a forced-induction engine is the factory head for the supercharged LS9 engine. Based on the 6.2-liter LS3/L92 head’s port and chamber design, it is made of a premium alloy and manufactured with a unique “roto-cast” process that spins the mold as the molten aluminum is poured to provide a more even, denser casting that all but eliminates porosity. They are available over the counter under PN 12621774. The LS9 heads, however, do not have a six-bolt design, but use larger 12-mm head bolts to increase clamping strength (other LS engines use a mix of 11- and 8-mm bolts). Adapting them to other LS engines requires resizing the head-bolt holes in the block to accommodate them. (Photo courtesy General Motors)
The telltale CNC porting finish on this head reveals a comparatively expensive machining job that won’t necessarily pay off with substantially greater performance. The general design of LS heads is very well suited to forced induction, with large intake runners and well designed combustion chambers. It is true that porting and other machine work can achieve flow characteristics that typically can’t be matched with an as-cast head, but the effect of that work is marginalized because the supercharger or turbocharger is cramming as much air into the chambers as they can take. My recommendation? Unless the heads are offered in a CNC-ported design out of the box, leave porting for naturally aspirated engines.
Additionally, a large number of companies offer modified versions of production GM heads that typically include CNC port work. These ported heads offer notable flow increases that are helpful on cathedral-port heads, but their relative expense doesn’t provide as much of a return on investment on the high-flowing rectangular-port heads. As-cast rectangular-port heads flow very well for supercharged and turbocharged engines.
Stainless-steel intake valves are hard to beat when it comes to strength and heat resistance. High-boost supercharged and turbocharged engines should employ thermally active exhaust valves, such as sodium-filled or inconel material, to withstand severe heat. The largest valves used in production LS engines are the LS7’s 2.20-inch intake and 1.61-inch exhaust valves.
Surprisingly, no production LS engines use roller-tip rocker arms; they’re all stamped-steel, flat-tip rockers. Later, rectangular-port heads use offset intake-side rocker arms (as seen here) that accommodate the valve position for both the large valve heads and the large ports within the head. Beehive-style tapered valve springs are LS-standard, too, but don’t stand up well to the increased pressure from a higher-lift cam or the cylinder pressure of high boost.
Shaft-mount rocker arms, such as the Jesel Pro J2K 1.8:1-ratio rockers (seen here), offer exceptional stability and virtually eliminate problems with valve lash as the engine quickly revs to the upper-RPM band. However, valve cover clearance is an issue when using shaft-mounted rockers, requiring machining of the valve cover rails on the heads and/or a valve cover spacer to prevent interference. Some aftermarket heads, such as World Products’ Warhawk heads and GM Performance Parts’ LSX heads, are cast with taller rails to accommodate taller rocker-arm assemblies.
Valves
Superchargers and turbochargers, especially turbochargers, generate more heat than a normally aspirated combination. Valves with the strength to withstand that heat are critical to the engine assembly. The factory-supercharged LS9 engine of the Corvette ZR1, for example, uses titanium intake valves and sodium filled exhaust valves.
The titanium valves are extremely durable and low in mass, but comparable performance and heat resistance can be found with stainless-steel intake valves, although they don’t have the weight advantage of titanium. As for the exhaust side, the use of sodium-filled valves have long been an effective way to combat exhaust heat, but like titanium intake valves, inconel-material exhaust valves offer a less-expensive, yet heavier alternative. Also, some builders shy away from sodium valves because of their multi-piece construction and resulting damage that could occur if the pieces separate at high RPM, but contemporary products have proven very durable.
Valvetrain Components
Stronger, higher-rate valve springs typically go hand in hand with higher-lift camshafts, but even if the camshaft profile remains relatively close to the stock cam, the boost pressure of a forced-induction engine generally demands stronger springs. That’s because the increased pressure in the cylinders wants to push the valves open or, at the very least, make it more difficult for them to close—and the greater the boost, the stronger the springs need to be.
Lifter type plays a role here, too, as a roller-type lifter can withstand about twice the valve spring pressure of a flat-tappet type. High spring pressure and high boost can affect the longevity of the camshaft, however, as greater pressure is transferred to it. So, a roller lifter is strongly recommended.
Production LS engines use non-roller rocker arms with, generally, a 1.5 or 1.6:1 ratio. Using roller-tip rocker arms reduces friction and a higher-ratio arm (typically 1.7 or 1.8:1) delivers the effect of a mild increase in cam lift. But because of the intake-side pushrod position on LS7/LS3/L76/L92 heads, the rocker arms are offset. There are few choices currently for roller-tip rockers for these offset-style arms, but SLP Performance has a set that fits LS3, L76, and L92 engines (PN 50189). The rockers have a 1.85:1 ratio.
Stronger-than-stock valve springs are recommended with increased ratio rockers.
Although there are several choices for roller-tip rocker arms for the conventional rocker arms of LS cathedral port heads, there are only a couple options when it comes to upgrading rectangular-port heads with offset rockers. T&D Machine Products offers these 1.7:1-ratio, shaft-mount roller-tip rockers for rectangular-port heads.
Higher-rate valve springs are a must on a purpose-built forced-induction LS engine, especially if the combination includes a camshaft that exceeds about .510-inch lift. Shown here are the components of Comp Cams’ 1.30-inch dual-coil valve spring, which withstands up to .600-inch lift without binding. The dual-coil design is heavier than the production-style beehive design, but offers exceptional strength and resistance to boost pressure. Using titanium retainers with the springs helps offset their additional weight over the stock springs.
A premium, multi-layer steel head gasket is an absolute must when building a force-inducted LS engine, particularly on higher-boost engines that don’t have the benefit of six-bolt head clamping. Fel-Pro and Cometic Gasket manufacture what have become the preferred gaskets for professional builders.
The factory LS9 cylinder head gasket is comprised of a whopping seven layers of specially treated steel. It fits other 6.2-liter engines (PN 12622033), but its added thickness when compared with standard four layer gaskets slightly reduces the compression ratio. That’s perfectly acceptable on a supercharged or turbocharged engine. (Photo courtesy General Motors)
This tech tip is from the full book, HOW TO SUPERCHARGE & TURBOCHARGE GM LS-SERIES ENGINES.
For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE
SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://www.lsenginediy.com/how-to-build-an-ls-engine-heads-cam-and-induction/
Cylinder-Head Gaskets
Because cylinder head sealing is crucial for forced-induction LS engines, the head gasket is a vital component in building a durable engine that stands up to great pressure. The factory-style gasket is a multi-layer steel (MLS) design that has proven very strong and reliable in naturally aspirated conditions and lower-boost engines of up to about 700 to 750 hp. However, the pressure of a supercharger or turbocharger, particularly when used with production-style four bolt cylinder heads, often makes the head gasket one of the primary failure points on otherwise-stock engines.
The MLS head gaskets from Ohio-based Cometic Gasket have proven to be very strong and durable in forced-induction engines—and most importantly, they’re available in a variety of bore sizes for the six bolt pattern of the GM LSX block and the RHS LS Race Block. They are constructed of two embossed, Viton-coated stainless-steel outer layers sandwiched around a variable stainless inner layer.
Also, Fel-Pro’s four-layer gaskets have proven to be very durable at higher horsepower. Copper gaskets or O-ring-style gaskets are suggested for racing engines producing more than 2,000 hp.
Camshaft
The camshaft needs for forced-induction engines are different than those for naturally aspirated engines. And while supercharged and turbocharged engines both feed pressurized air to the combustion chambers, there are differences that can affect the optimal camshaft profile, particularly the exhaust duration.
Before getting into the specifics of camshaft selection, here’s a quick primer on common cam terms.
Lift: The distance the valve head is raised off its seat when the camshaft lobe is at its highest position (and in combination with the rocker arm). Lift is measured in fractions of an inch or millimeters. In theory, greater lift enhances performance by creating a wider opening to the combustion chamber and allowing a larger air/fuel charge to be packed in it.
Duration: The amount of time a valve is held open, measured for both the intake and exhaust valves in degrees of crankshaft rotation; i.e., 250 degrees on the intake valve and 255 degrees on the exhaust side. In general terms, longer duration enhances performance at higher RPM or helps extend the RPM range of the engine.
Camshaft selection is very important when it comes to maximizing the performance of a force-inducted engine. In general terms, both supercharged and turbocharged engines respond best with a camshaft that has a lobe-separation angle of around 114 degrees, but the nature of how boost is produced and processed (including the role of overlap) requires markedly different approaches to the duration specifications.
A solution to the longtime debate between high-power street/strip and racing-oriented engines is the use of a hydraulic-roller camshaft versus a solid-roller cam. As with normally aspirated engines, a hydraulic roller cam is suitable for high-power street and street/strip engines. It’s not until the engine is expected to turn extremely high RPM and the cam’s lift specs reach the .750-inch range (and higher) that the more positive valvetrain actuation offered by a solid roller is required.
Lobe/Lobe Ramp: The part of the camshaft that interfaces with the lifter, with the ramp section being the part that initiates the lifting and descending of the lifter. The profile of the lobe determines the speed or rate at which the valve opens and closes.
Symmetrical/Asymmetrical Lobe Ramps: A camshaft with symmetrical lobes has matching opening and closing ramps on both the intake and exhaust. An asymmetrical cam has different opening and closing ramp profiles on each lobe.
Base Circle: The lowest point of the camshaft lobe and the place in the camshaft’s rotation when the valve is completely closed. Lobe
Separation Angle: The distance in camshaft degrees between the maximum lift points of both the intake and exhaust valves. It affects performance by affecting valve overlap to impact the overall performance range of the engine. In a nutshell, a narrow angle promotes a steep, immediate power curve and a wider angle spreads the power out across the RPM band. Valve
Overlap: Measured in degrees of crankshaft rotation, it’s the amount of time both the intake and exhaust valves are opened in a combustion chamber. It takes place as the exhaust stroke ends and the intake stroke begins. In general terms, greater overlap builds power at higher RPM by helping pull the fresh air/fuel charge into the chamber. Great lift and duration increases overlap, as does reducing the lobeseparation angle.
Intake Centerline: The point of greatest lift on an intake lobe, measured in crankshaft degrees after top dead center. In an assembled engine, it is measured by the crankshaft degrees between top dead center and the point of maximum valve lift.
Hydraulic Flat Tappet vs. Hydraulic Roller: All production LS engines feature hydraulic lifters, but not hydraulic roller lifters, which are the friction-reducing rollers that interface with the cam’s lobe ramps.
In general, a camshaft for a supercharged or turbocharged engine should have a wider lobe-separation angle (LSA) than a naturally aspirated engine in order to spread the power across the RPM band and deal with the increased cylinder heat that comes with forced induction. The rule of thumb for the LSA is 112 to about 114 degrees, although several LS engines’ stock cams feature a 112- degree LSA—and the LS2 cam’s LSA spec is a wide 116 degrees, for example, while the factory supercharged LS9’s lobe-separation angle is an extra-wide 122.5 degrees.
The optimal LSA must be matched with the appropriate exhaust duration to better handle exhaust pressure. Again, in general terms, a supercharged engine needs more exhaust duration than a naturally aspirated engine, while a turbocharged engine needs less duration.
Turbocharger Camshaft
Generally speaking, a turbocharged engine benefits from a milder cam (one with lower duration) in order to make the most of the exhaust-gas pressure that drives the turbocharger’s turbine. In a nutshell, the camshaft should be used to keep heat out of the cylinders.
Ideally, the boost pressure of a turbo engine should be greater than the exhaust pressure at the low end of the power band, as the engine nears its peak torque. The boost pressure and exhaust-gas pressure are nearly equal when the engine approaches its peak horsepower. However, at peak horsepower there is typically greater exhaust back pressure than boost.
For optimal efficiency and maximum effectiveness of the turbo system, the boost should exceed (or at least be equal to) the exhaust back pressure over the RPM range. When this doesn’t occur, a too-small turbocharger can be the culprit.
The original LS7 engine’s cam had .591/.591-inch lift, 211/230 degrees duration and 121-degree lobe separation angle specs. Katech Performance used a camshaft with greater lift (.615/.613-inch) to maximize airflow; slightly more intake valve duration (220 degrees) and less exhaust valve duration (229 degrees). The cam’s lobe separation angle was also dialed back to a more appropriate 116 degrees.
The LSX iron cylinder block can be machined for a Jesel belt-drive timing-belt system.
The reason a turbo engine needs less duration than the supercharger cam is because the turbocharger itself is an exhaust restriction that increases exhaust gas pressure— and it’s the exhaust-gas pressure that spins the turbo. Therefore, a milder cam with lower duration helps exploit boost-enhancing exhaust gas pressure.
A supercharged engine’s boost is generated at the front of the engine’s air stream, so a cam with greater duration than what would be used with a turbo engine helps expel exhaust gases more completely, clearing the chamber and promoting unrestricted airflow. But as Comp Cams’ Billy Godbold pointed out, the camshaft for any forced-induction engine should have less overlap to prevent boost from escaping through the exhaust port.
An important note about the above samples: They are meant to provide an illustrated comparison and shouldn’t be considered recommendations for any LS forced induction engines. Factors determining the “perfect” camshaft grind include the size of the supercharger or turbo compressor; the displacement of the engine; cylinder-head changes over stock; and even the type of performance expected—i.e. street, street/ strip, or dedicated racing.
Ignition and Ignition Controller
The production-style coil-nearplug ignition system is surprisingly good for even moderately high boost pressure—up to about 12 to 15 pounds. As boost pressure increases, a higher-energy spark system is required because the higher pressure can effectively blow out the spark before it can jump the gap on the spark plug (much like trying to light a match in the wind). A few aftermarket companies, including MSD Ignition and ACCEL, offer replacement coil packs that provide greater energy than GM’s factory units. That greater energy helps light the mixture under pressure, while also ensuring a more complete burn.
On racing engines, where high boost and high RPM define the engine’s primary operating parameters (those making approximately 1,500 hp and more) the sequentially triggered individual-coil system has neither the energy nor speed to deliver adequate and dependable ignition control, even when using hotter aftermarket coils. The alternative is converting the engine from the production-style crank-triggered system to a conventional distributorbased system that is also linked to a high-energy coil.
Fortunately, the tools for the conversion are already on the market, thanks to circle track series’ that require distributor-driven ignition systems. To support them, GM Performance Parts offers a conversion kit (PN 88958679) that happens to be perfect for force-inducted racing engines. The kit provides the distributor-mounting fixture for the front of the engine, as well as the distributor drive gear that is attached to the camshaft. From there, a standard distributor and coil are used.
“It’s the only way to ensure adequate spark energy, with the cylinder pressure and speed that the engine achieves so quickly,” says experienced LS engine builder Brian Thomson.
The production-style individual-coil system works very well for even heavily modified engine making up to 1,000 hp or more. Aftermarket coils, such as these from MSD Ignition, provide more energy that is helpful on engines with higher boost levels.
ACCEL is another source for hotter-than-stock ignition coils. The greater energy helps the flame of the spark withstand boost pressure that wants to blow it out, much like blowing out a match.
When the individual-coil system reaches its limit, the only alternative is conventional distributor-driven ignition system. GM Performance Parts offers the conversion kit, which mounts to the front of the engine, under PN 88958679. A conventional distributor, such as the front-mount type for a Ford Windsor small-block, is used with it.
It’s not that the intake manifold isn’t important on a force-inducted LS engine, but because of the pressurized delivery of air, it’s less of a factor in the ultimate performance of the engine. The factory intake manifolds work well with superchargers and turbochargers, so replacing them with aftermarket manifolds isn’t necessary for most applications.
“The factory coil system is very good for even 1,000-hp combinations, but at this level, something stronger is needed.”
Thomson used the distributor conversion system on the 2,000-hp, twin turbo LS engine project on page 129.
Intake Manifold
In a general sense, the intake manifold doesn’t have as great an impact on the output of a forced induction engine, as the boost pressure largely overrides a manifold’s plenum volume and runner design. That said, the intake should offer low restriction and a straight path to the combustion chambers.
For vehicles used primarily on the street, a production-style intake manifold with greater plenum volume helps maintain low-end torque for greater low-speed drivability on the street, when the engine isn’t under boost. Bolt-on supercharger and turbo kits—even those used on modified, purpose-built short-block assemblies—perform very well on the street and drag strip with production intake manifolds, including factory-style intakes from aftermarket companies, such as F.A.S.T. Vehicles designed primarily for drag racing, where the engine will spend most of its time at higher RPM, benefit from a carbureted-type “spider” aluminum manifold that has shorter, direct, and straight intake runners. These manifolds are readily available from several aftermarket companies, as well as GM Performance Parts. Using one with a high-boost turbo or supercharger system requires an adapter and/or elbow on top of the manifold, as well as an intake tube, to feed the manifold. These are generally custom-built parts, as the engines that employ such induction systems are typically custom built.
When selecting a spider-type intake manifold, be sure to match it with the cylinder-head intake-port design. The manifolds are designed to match the cathedral-port and different rectangular-port configurations of LS heads. Also, adapter plates are needed (perhaps requiring custom fabrication in some cases) when using any intake manifold with a tall-deck cylinder block, as the heads are pushed out farther than on an engine with a standard deck block.
For safety reasons, an aluminum or sheet metal intake should also be considered for racing-oriented engine combinations that will see 20 pounds of boost or more. Rather than being cast as a single part, the nylon/plastic production-style intake manifolds are generally comprised of multiple pieces that are assembled with adhesive bonding agents. They weren’t designed for the extreme pressure that comes with high boost and inadvertently discovering the pressure point at which the components separate or the brittle nylon material shatters is not something a racer wants to discover on the starting line.
The use of a carbureted-style aluminum intake manifold comes with racing applications that will see very high boost pressure and require custom plumbing to route large diameter tubing through the engine compartment.
This photo shows a typical racing setup that uses a carbureted-style intake with an elbow designed to accept the injection system’s throttle body. The aluminum intake also provides a measure of safety for high-boost engines, as the cast aluminum is less likely to shatter than the brittle nylon material of a production intake.
This impressive-looking tunnel-ram style intake has a fatal flaw for high-boost forced induction: As air rushes through the front of the manifold under pressure, it packs into the rear intake runners, leaving the front runners relatively starved. A better solution would be to introduce the air at the top of the manifold, where the airflow would be better spread among the runners.
Most off-the-shelf aluminum manifolds for LS engines are of the carbureted/spider style, although Holley offers an aluminum, production style manifold (PN 300-111) for LS1/LS6 engines.
Throttle Body
The throttle body must be compatible with the engine-control module, particularly when using a GM controller that is calibrated for either a cable-operated or electronic throttle. For most street/strip combinations of up to 1,000 hp, or so, a production GM throttle body, such as LS7’s large, 90-mm unit, works and flows just fine.
It is possible to adapt an electronically controlled throttle to a vehicle originally equipped with a conventional cable throttle and vice versa, but modifications are required, including changing the engine controller and pedal assembly, and is generally not worth the time. If the vehicle was originally equipped with a cable throttle, use a larger, cable-actuated throttle body if necessary; and if the vehicle came with an electronic throttle, continue using the same type.
Fortunately, GM cable-operated and electronic throttle bodies are generally interchangeable on intake manifolds, so a cable throttle body can be used on an LS7 intake manifold, allowing for example, this high-flow intake to be used in a fourth-generation F-body with a cable-operated throttle system.
Cable-operated throttle bodies are manufactured in a number of very large sizes to suit high-power racing engines, but options for engines with electronically controlled throttles are limited. Some companies offered ported and modified versions of production throttle bodies, but their effectiveness is limited, as they simply don’t offer a significantly larger flow path for the air charge.
The 90-mm electronic throttle body found on LS7 and LS9 engines (they are of similar diameters, but not the same part), is sufficient for 6.2-liter and smaller engines, making up to approximately 1,000 hp. With larger displacement engines, the airflow requirements are greater and the 90-mm unit runs out of breath around the 750- to 800-hp level.
Dedicated race cars should use a cable throttle for maximum driver control. In fact, for safety reasons, many sanctioning bodies require it. Also, the airflow requirements of a 1,500- to 2,000-hp engine can’t be met with current production-based electronic throttle bodies.
This tech tip is from the full book, HOW TO SUPERCHARGE & TURBOCHARGE GM LS-SERIES ENGINES.
For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE
SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://www.lsenginediy.com/how-to-build-an-ls-engine-heads-cam-and-induction/
Electronic Throttle Bodies and Blow-off Valves
Some builders have reported a condition with supercharged LS engines that use electronically controlled throttle bodies where excessive boost pressure pushes on the throttle blade after it is closed— such as when the driver takes his foot off the gas—forcing unwanted air into the engine. At the least, it can cause stumbling and other drivability issues, but it could also lead to engine damage if the excessive airflow causes a lean condition.
The problem can be due to an inadequate supercharger blow-off valve (in many cases, the issue has been reported with Eaton-type Roots superchargers) that doesn’t bleed off enough boost pressure when the throttle closes. It can also be due to a throttle body with a throttle blade spring that doesn’t have sufficient strength to keep the blade closed. Or it could be a combination of both issues.
Some enthusiasts have had success swapping the throttle body with a strong factory unit, such as the LS3 unit from the C6 Corvette; however, it requires additional tuning to match the throttle body with the engine controller. A stronger or larger bypass valve is another solution.
Written by Barry Kluczyk and Posted with Permission of CarTechBooks
LEARN MORE ABOUT THIS BOOK
If you liked this article, you will LOVE the full book!
Get your copy here.