Читать книгу How to Supercharge & Turbocharge GM LS-Series Engines - Revised Edition - Barry Kluczyk - Страница 8

CHAPTER 1

LS ENGINES AND FORCED INDUCTION

In general terms, and assuming everything else is equal, an internal combustion engine with larger displacement flows more air than a smaller-displacement engine. The engine with the greater airflow makes more power.

Forcing more air into an engine than it naturally draws can substantially increase the output of a smaller engine and give it the power of a larger engine. The forced or ambient air is delivered to the intake manifold at a pressure greater than the outside. It is denser, delivering more oxygen to the combustion chamber. When mixed with the appropriate ratio of additional fuel, the result is a more powerful combustion. That’s the essence of supercharging; whether through an engine-driven supercharger or exhaust-driven turbocharger.

The technology for forced induction supercharging and turbocharging internal combustion engines has been around since the early 20th century, with automotive manufacturers employing the power-boosting effects for more than 80 years. Both supercharging and turbocharging are currently used on dozens of regular production automobiles, and they have been staples of the high-performance world since the close of World War II.

Forced induction has been used to boost the power of engines for decades. Hot rodders made it a common practice after World War II, and engine-driven supercharging became popular on street and drag racing cars.

One of the most popular performance engines of today is GM’s “LS” family. As technology progresses, it continues to become an increasingly popular choice for forced induction. Since its introduction in the late 1990s, the GM Gen III/Gen IV engine family (commonly known as LS) has proven itself as a capable foundation for high-performance engines. By relying on a conventional, cam-in-block configuration with the benefit of exceptionally high-flowing cylinder heads, the LS engine delivers tremendous torque at low RPM and great power at the upper rev range.

General Motors experimented with turbocharging in the early 1960s and perfected it in the mid-1980s by combining it with electronic fuel injection. The turbocharged and intercooled V-6 engine of the 1986–1987 Buick Grand National outperformed most V-8s when new.

Forced induction was attempted with early LS engines, often with mixed results. Early adopters of supercharging and turbocharging typically encountered tuning trouble when they tried to work around the factory engine-control system and crank-triggered ignition system. That, and the greater airflow capability of the LS heads, made it difficult to match a supercharger or turbocharger to the engine. Often, the blowers ran out of breath.

In the early 1990s, General Motors adopted supercharging for a number of V-6-powered midsize and large passenger cars, including the Pontiac Grand Prix. The automaker used a Roots-blown 3.8L engine with a supercharger supplied by Eaton. The engines proved exceptionally robust and powerful, spawning a cult of enthusiasts who continue to modify and race the vehicles.

But much has changed in the years since tuners first experimented with supercharging the LS engine. Properly sized superchargers and turbochargers, relatively easy tuning, and other elements have made supercharging or turbocharging an LS-powered vehicle a simple, yet highly effective, method of generating a dramatic increase in power.

Of course, General Motors itself has adopted supercharging as a regular production method of building big power. The C6 Corvette ZR1’s LS9 engine and the Gen II Cadillac CTS-V’s LSA engine used Roots-type superchargers to make 638 hp and 556 hp, respectively. The engines were also designed with specific components to support forced induction.

GM’s relationship with Eaton superchargers reached its zenith in 2009 with the introduction of the factory-blown Corvette ZR1. With its sixth-generation supercharger atop its 6.2L V-8, the ZR1 is rated at 638 hp. It is the most powerful production car ever produced by General Motors. (Photo Courtesy General Motors)

Along with the Corvette ZR1, General Motors launched another factory-supercharged car in 2009: the Cadillac CTS-V. Like the ZR1, it featured a sixth-generation Eaton supercharger on a 6.2L engine, but the supercharger was smaller, resulting in only 556 hp. (Photo Courtesy General Motors)

LS Family Tree

The engine family commonly called the LS series debuted in 1997. General Motors called it the Gen III Small-Block with the iron-block versions in trucks and the all-aluminum LS1 version introduced in the then-new C5 Corvette. A year later, the LS1 replaced the Gen II LT1 Small-Block in Camaros and Firebirds. The LS1 displaced 5.7 liters, similar to the previous-generation small-block, but the cubic-inch measurement differed slightly: 346 for the LS1 versus the traditional 350.

An LS1 5.7-liter Gen III is shown. (Photo Courtesy General Motors)

In 1999, the Gen III platform spawned the higher-performance LS6 that was standard in the Corvette Z06. In 2005, the Gen IV branch of the LS family was born, differing from the Gen III with cast-in provisions for fuel-saving cylinder deactivation, larger displacements, and revised camshaft sensing. The performance versions of the Gen IV include the LS2, LS3, LS9 supercharged, and LS7.

This is an LS3 6.2-liter Gen IV. (Photo Courtesy General Motors)

GM has continued to refer to its modern V-8 engine family as Gen III and Gen IV, but to the enthusiasts who quickly grasped the tremendous performance potential of the engines, every engine based on the platform is nicknamed “LS.” The range of production engines from the LS platform is wide. On the truck side, iron-block engines have included 4.8L and 5.3L versions, as well as all-aluminum 6.0L and 6.2L premium engines. Car engines include 5.3L, 5.7L, 6.0L, 6.2L, and 7.0L displacements, including some configured for front-wheel drive.

Gen III Versus Gen IV

Despite some significant differences between Gen III and Gen IV cylinder blocks, all LS engines share common traits that include:

• 4.400-inch bore centers (matching the original small-block)

• Six-bolt, cross-bolted main bearing caps

• Center main thrust bearing

• 9.240-inch deck height

• Four-bolts-per-cylinder head bolt pattern

• 0.842-inch lifter bores

• Distributorless, coil-near-plug ignition system

The most distinguishing differences between Gen III and Gen IV cylinder blocks are larger bores (on some engines), different camshaft position sensor locations (front timing cover area on Gen IV blocks and top-rear position on Gen III blocks), and on most Gen IV blocks, cast-in provisions for GM’s Active Fuel Management cylinder deactivation system.

There is great interchangeability between all LS engines, including between Gen III and Gen IV versions. Cylinder heads, crankshafts, intake manifolds, and more can be mixed and matched, but the devil is in the details. Not every head matches every intake manifold and not every crankshaft works with every engine combination. Will Handzel’s How to Build High-Performance Chevy LS1/LS6 V-8s is a great reference source that outlines the more specific differences and interchangeability among Gen III-based engines.

LS1/LS6

LS1 5.7L (346-ci) engines were produced between the 1997 and 2004 model years in the United States (Corvette, Camaro, Firebird, and GTO) and stretching into 2005 in other markets (primarily Australia). The LS6 was introduced in 2001 in the Corvette Z06 and was manufactured through 2005, where it also was found in the Cadillac CTS-V. The LS1 and LS6 share a 5.7L displacement, but the LS6 production engine uses a unique block casting with enhanced strength, greater bay-to-bay breathing capability, and other minor differences. The heads, intake manifolds, and camshaft also are unique LS6 parts.

LS2/L76/L77

In 2005, the LS2 6.0L (364-ci) engine and the Gen IV design changes debuted. In GM performance vehicles, it was offered in the Corvette, GTO, and even the heritage-styled SSR roadster. It was the standard engine in the Pontiac G8 GT (L76) and is now the V-8 offered in the Chevrolet Caprice Police Pursuit Vehicle (L77). This engine is one of the most adaptable in the LS family, as LS1, LS6, LS3, and L92/L94 cylinder heads work well on it.

LS3/L99

Introduced on the 2008 Corvette, the LS3 brought LS-based performance to an unprecedented level: 430 hp from 6.2L (376 ci). The LS3 block not only had larger bores than the LS2 but also a strengthened casting to support more powerful applications, including the LS9 supercharged engine of the Corvette ZR1. The LS3 was also the standard engine in the fifth-generation Camaro SS and was offered in the Pontiac G8 GXP. The L99 version was equipped with GM’s fuel-saving Active Fuel Management cylinder deactivation system and was standard on fifth-generation Camaro SS models equipped with an automatic transmission. A unique version of the LS3 used in some C6 Corvette Grand Sport applications incorporated a dry-sump oiling system.

LS4

Perhaps the most unique application of the LS engine in a car, the LS4 was a 5.3L version used in the front-wheel-drive Chevrolet Impala SS and Pontiac Grand Prix GXP. The LS4 had an aluminum block and unique, low-profile front-end accessory system, including a “flattened” water pump, to accommodate the transverse mounting position within the Impala and Grand Prix. It was rated at 303 hp and 323 ft-lbs of torque.

LS7

A legend in its own time. The LS7 was the standard engine in the C6 Corvette Z06 and fifth-generation Camaro Z28. Its 7.0L displacement (427 ci) made it the largest LS engine offered in production vehicles. Unlike LS1/LS6, LS2, and LS3 engines, the LS7 uses a Siamese-bore cylinder block design, which was required for its big 4.125-inch bores. Competition-proven heads and lightweight components, such as titanium rods and intake valves, made the LS7 a street-tuned racing engine with 505 hp. Chevrolet Performance’s crate engine reflects the Camaro Z28 version, which features a unique Tri-Y exhaust manifold design.

LS9

The LS9 was the 6.2L supercharged and charge-cooled engine of the C6 Corvette ZR1, rated at 638 hp. The LS9 used a strengthened 6.2L block with stronger roto-cast cylinder heads and a sixth-generation 2.3L Roots-type supercharger. Like the LS7, it used a dry-sump oiling system.

Pictured is an LSA 6.2-liter supercharged Gen IV. (Photo Courtesy General Motors)

LSA

This supercharged 6.2L engine powered the 2009–2015 Cadillac CTS-V series and the 2012–2015 Camaro ZL1. Although similar to the LS9 in design, it was built with several differences, including hypereutectic pistons versus the LS9’s forged pistons and a smaller 1.9L supercharger. It also has an eight-bolt flywheel versus the LS9’s nine-bolt pattern. The LSA has a unique charge-cooler design on top of the supercharger (with differences between the Cadillac and Camaro ZL1 applications). It was rated at 556 hp in the CTS-V and 580 hp in the Camaro ZL1. Chevrolet Performance’s crate engine reflects the Camaro ZL1 application.

Gen III and Gen IV Vortec Truck Engines

Although performance car engines have typically carried “LS” designations, truck engines built on this platform have been dubbed “Vortec.” They are generally distinguished by iron cylinder blocks and smaller displacements than car engines. Interestingly, a 5.7L Vortec “LS” engine has never been offered. Here’s a quick rundown of production LS truck engines.

4.8L: The smallest-displacement LS engine (293 ci); it uses an iron block with 3.78-inch bores and aluminum heads.

5.3L: The most common LS truck engine, it uses the same iron block with 3.78-inch bores as the 4.8L, but with a larger, 3.62-inch stroke (327 ci). Later versions equipped for Active Fuel Management and 2010-and-newer versions feature variable valve timing (cam phasing). Manufactured with iron and aluminum cylinder blocks.

6.0L: Used primarily in 3/4-ton and 1-ton trucks, the 6.0L (364 ci) uses an iron block (LY6 or L96) or aluminum block (L76) and aluminum heads with provisions for Active Fuel Management; some are equipped with variable valve timing.

6.2L: Commonly referred to by its L92, L9H, or L94 engine codes, the 6.2L (376-ci) engine uses an aluminum block and heads and incorporates advanced technology, including variable valve timing. The L92 was used primarily as a high-performance engine for the Cadillac Escalade and GMC Yukon Denali.

More About the Vortec 5.3L

With more than 10 years in service in millions of Chevy and GMC trucks, vans, and SUVs, the Vortec 5.3L engine is poised to become the classic 350 small-block of the LS engine family. They are readily available and affordable on the used engine market. Most feature iron cylinder blocks, but some have an aluminum engine block that is about 80 pounds lighter.

Adapting a 5.3L to a hot rod project is easier with Chevrolet Performance’s 5.3L controller kit (part number 19256514), which is tailored to retrofit installations by “turning off” some of the production features that are unnecessary for a vintage car, including the cylinder-deactivating Active Fuel Management. It covers 2007–2009 applications (non-cam-phased) with the following engine codes:

• LC9 (2007–2009)

• LMG (2007–2009)

• LY5 (2007–2009)

• LH8 (2008–2009)

• LMF (2008–2009)

An L94 Vortec 6.2L Gen IV is shown. (Photo Courtesy General Motors)

Chevrolet Performance LS and LSX High-Performance Crate Engines

Chevrolet Performance has offered a number of LS high-performance crate engines based on production LS engines or the racing-oriented LSX series of components, including the cast-iron LSX Bowtie Block. They include:

LS376/515: Based on the LS3, it features the “ASA Hot Cam” to help push output to 525 hp and 477 ft-lbs of torque. It is designed for a carburetor.

LS376/525: Similar to the LS376/515, this version also uses the ASA Hot Cam, along with an LS3-based induction system and port fuel injection.

LSX376-B8: An economical crate engine that uses the LSX block, LS3 rotating parts, and the LS3 cylinder heads. It is offered without an oil pan or induction system, so that it can be tailored for the project vehicle.

LSX376-B15: Designed to accommodate additional power adders, or boost up to 15 psi, includes forged pistons, forged crank, and six-bolt LSX-LS3 cylinder heads.

LSX454: The displacement of the classic big-block with an all-forged rotating assembly and LSX-LS7 six-bolt cylinder heads. It is rated at 627 hp with a carburetor and 580 with an LS7 fuel-injection system.

Excellent airflow characteristics of the basic LS cylinder head design greatly exploit the benefits of forced induction, as air is easily and quickly moved through the engine. Because of this, a higher-capacity supercharger or larger turbo is often used, when compared to older, previous-generation Chevy small-block designs, to fulfill the airflow capability of a free-flowing LS engine.

LSX454R: A high-compression (13.1:1) version of the LSX454 designed for drag racing, featuring a mechanical roller cam, high-rise intake, and more. It is capable of more than 750 hp.

Supercharging Versus Turbocharging

At their most basic, turbochargers and superchargers are air pumps but with different pumping characteristics. The turbocharger is an exhaust-driven pump that saps no engine power when not making boost. A supercharger is an engine-driven pump that is essentially another component on the accessory drive system and requires a modicum of power to drive, even when it’s not producing much or any boost.

The thermal efficiency, also known as adiabatic efficiency (the amount of combustion energy that is converted to power), is generally greater with a turbocharger system than a supercharger because it recycles a significant amount of exhaust energy to spin the compressor. That exhaust energy is lost to the exhaust system in normally aspirated and supercharged engines. That said, centrifugal and Lysholm (screw-type) superchargers can be up to 85-percent efficient, for comparable efficiency with a turbocharger.

In general terms, superchargers deliver greater power and torque at low- and mid-range RPM levels with nearly full boost available immediately at wide open throttle (WOT). A supercharger’s effectiveness tends to trail off at higher RPM, while turbochargers typically deliver their greatest power contribution at mid- to high-RPM levels, with boost building progressively in line with an increase of engine speed. Turbochargers are also very good at building mid-range torque, and when properly sized, can deliver excellent low-end power too.

There are a number of factors to consider before purchasing a bolt-on system. The performance requirements and engine demands for custom combinations and racing applications are different, but for the enthusiast seeking to add a forced-induction system to his or her vehicle, the following points are the most relevant.

Superchargers (particularly Roots and screw-type blowers) are excellent at delivering low-RPM power, as they are always making at least a minimal amount of boost when the engine is running. That’s because the supercharger is directly linked to the crankshaft via the drive belt. That connection also requires a small amount of horsepower to simply turn the supercharger.

Power Projections

Generally speaking, a supercharger will produce about 6 percent greater horsepower for every pound (0.07 bar) of boost, while a turbocharger will produce about 7 percent greater power for every pound. The turbo’s advantage there is due to the parasitic loss of the supercharger’s drive system. It simply costs some power for the crankshaft to drive the blower. The exhaust-driven turbocharger doesn’t have such a drag.

Turbochargers require no engine power to drive and, therefore, are considerably more efficient than an engine-driven supercharger. However, boost only occurs when the engine RPM rises. At low speeds, particularly off idle, the turbocharger provides no horsepower increase.

The advantage of turbocharging in a racing application is clearly illustrated in this partially constructed fourth-generation Firebird, as two very large turbochargers were adapted to an LS engine. Except for the older, “71”-series superchargers used in Top Fuel, Top Alcohol, and some Pro Mod–type drag racing classes, there aren’t Roots and screw-type superchargers that deliver the airflow of a pair of extra-large turbos. Even large centrifugal blowers are limited to only one per engine. With a pair of turbos, each driven by half of the cylinders, the only real limit is keeping the engine itself together under maximum boost.

Apart from the capacity to change the drive pulley on some superchargers, the output of a blower is pretty much determined by the size of the compressor. With a turbo system, a number of elements are easily manipulated to increase power. In fact, the almost-infinite adjustability of turbo systems is one of their primary appeals.

Performance Range

As noted earlier, superchargers (particularly Roots/screw types) generally deliver gobs of low-end power and become less efficient at higher RPM. The opposite is generally true for turbochargers; they tend to deliver their greatest performance as maximum boost is delivered with higher engine speed.

Drivability

Because an engine-driven supercharger is always “on,” it tends to give a street-driven vehicle an abundance of off-the-line/low-speed pull; to the point where it is difficult to manage part-throttle driving in some instances, as tire spin becomes an issue. The higher-RPM power application of turbo systems typically makes them more tractable at low speeds. The enthusiast wishing for supremacy off the line at stoplights with the instant application of full boost will probably enjoy a supercharger; while the enthusiast seeking a wider performance range will likely find a turbo system more rewarding.

Modern Roots and screw-type superchargers make excellent choices for street-driven performance vehicles, as they deliver instant power at low speeds. They’re also quieter and offer greater drivability than ever before. And when compared to custom or bolt-on turbo kits, they are very cost effective.

Noise

Generally speaking, the compressors of most supercharger and turbocharger systems are very quiet these days. Turbos are essentially silent until they start spinning at high RPM, and the same is true for most Roots/screw-type blowers. Centrifugal superchargers are much quieter than they used to be, but at idle, they’re not as quiet as turbos or Roots/screw-type superchargers.

Tuning

There’s no real advantage between tuning a supercharged or turbocharged engine, as the need to maintain an adequate air/fuel ratio and optimal spark to avoid detonation is paramount with both methods. Both types of systems have unique needs for delivering safe, optimal performance, but the basic approach to tuning is similar. There’s no clear advantage to either system.

Maintenance and Reliability

When installed and used properly, supercharger and turbocharger kits are very reliable with the compressors for both lubricated with engine oil, although some Roots/screw-type blowers feature self-contained lubrication systems. Over time, the drive belt for a supercharger must be inspected just like the engine’s standard accessory belt, and after a few years, the compressor may require an inspection to ensure the tolerances and clearances are within specification limits for the rotors. Turbochargers are very susceptible to heat, and even with adequate lubrication, the internal seals and turbine can wear and allow oil blowby. This requires the turbo to be rebuilt.

System Cost

Because of a myriad of extra equipment (from the wastegate to the exhaust manifolds), turbocharger bolt-on kits generally cost two to three times more than supercharger kits. Additionally, turbocharger systems generally take longer to install than supercharger kits. This adds up when outsourcing the project to a professional shop.

A couple of the biggest advantages of a supercharger for a primarily street-driven vehicle is comparatively easy installation and a lower labor investment. Bolt-on kits (particularly Roots/screw-type systems that essentially swap out the original intake manifold) can be installed relatively quickly with little impact on the rest of the vehicle’s components or systems. The quicker the installation, the lower the labor cost at a professional shop.

Installation Impact on the Vehicle

Assuming all turbocharger and supercharger systems employ an intercooler, the Roots/screw-type supercharger systems generally require the fewest compromises and/or fabrication modifications during installation. Because they install in place of the intake manifold, few changes are required at the front of the engine or in the engine compartment. Consequently, they offer the most integrated, factory-looking appearance under the hood. Centrifugal superchargers require a mounting bracket on the front of the engine that can require moderate modification, removal, or relocation of factory components.

With bolt-on turbocharger systems, the installation of the exhaust manifolds, turbochargers, and associated plumbing typically require considerably more fabrication, modification, and relocation of stock parts than supercharger systems. An intercooled turbo system can also take up more real estate under the hood, particularly when using larger turbochargers. That can induce a number of fitment challenges that require additional fabrication to overcome.

Installation Cost

Again, because of the extra equipment associated with them, turbocharger kits are generally more time consuming to install, and therefore, there are more labor costs.

So, while a turbo kit offers greater performance potential, the cost involved with this investment may steer some toward a supercharger. In fact, there are other factors to consider before ordering a system for your car.

For one, the tight confines of the engine compartments in Corvettes, Camaros/Firebirds, and GTOs/Monaros make packaging and installing a turbo kit very difficult. This not only makes the installation a painstaking and difficult procedure but can make future servicing all but impossible without an extensive teardown of the vehicle’s front end.

There is more room in the engine compartments of full-size trucks, SUVs, and TrailBlazer SSs; but stuffing a turbo system can be a challenge in a regular street car.

My opinion is that turbocharging is great for vehicles destined to spend equal time on the street and strip; but for typical, street-driven vehicles, a supercharger system is the easier and more economical method to build power. Many tuners and manufacturers that fall on the turbo side of the argument will undoubtedly disagree; but when it comes to bolt-on, forced-induction kits, superchargers are easier and cheaper to implement with less maintenance.

Understanding Boost (Including PSI Versus Bar)

Whether it is a supercharger or a turbocharger system, the measure of pressurized air fed into the engine is referred to as “boost.” It is the difference between the ambient air pressure and the increased air pressure that the boost-producing device generates at the intake manifold. Boost is the opposite of vacuum, which is what a nonboosted engine makes during normal operation.

When an engine isn’t running, it generates no vacuum or boost (negative pressure), meaning the pressure in the intake manifold is the same as the ambient air pressure: about 14.7 pounds per square inch (psi). At idle and low-throttle conditions, an engine generates vacuum, indicating the pressure in the intake manifold is lower than the ambient pressure.

In a supercharged or a turbocharged engine, boost is created as more throttle is applied and the boost-generating device forces air into the intake manifold at a higher pressure than ambient (positive) pressure. The air pressure at the intake manifold swings from negative to positive; that’s why high-performance boost gauges indicate both vacuum and boost measurements.

Boost is generated when the supercharger or the turbocharger creates air pressure greater than ambient when it is introduced to the engine (at the throttle body). Supercharged engines generate a small amount of boost whenever the engine is running, even at idle. Turbocharged engines require higher RPM to generate boost.

In North America, boost is generally measured in PSI, while bar is more common in other countries. When measuring in psi, the ambient air pressure is regarded as the base, or 0 pounds of boost. The positive pressure builds on that base with 1 pound of boost indicating 1 psi greater than ambient pressure.

With bar measurements, bar is roughly the equivalent of ambient air pressure. Technically, 1 bar is equivalent to 14.7 psi, not 14.5 psi, but many enthusiasts equate it to the normal atmospheric pressure, so a 0.5-bar pressure reading is roughly 7.25 pounds of boost. A full, 1-bar reading would indicate 14.5 pounds of boost.

Drag Racing

Turbochargers are common among Outlaw-type drag racing classes, where the virtually unlimited boost potential from increasingly larger turbos has enabled tremendous power levels. Simply put, superchargers haven’t matched turbos for boost capability. That is changing with a new generation of larger, higher-flow superchargers, led primarily by ProCharger.

With the weight breaks offered to supercharged cars in many classes, the boost capability of the latest blowers puts racers on par with turbocharged competitors. Racer Tom Kempf, who has driven a turbocharged 10.5 Outlaw Firebird for more than a decade, is ready for the change.

“I’ve had a lot of success with turbochargers, but that has come with a number of compromises,” Kempf says. “First and foremost is these big, powerful turbo engines are very hard on transmissions, when it comes to staging and building boost at the starting line. That’s not an issue with a supercharger.”

Supercharger systems are much less complex than turbo systems with far less plumbing. That reduces fabrication time during the vehicle’s build and makes it easier to do between-round maintenance. The bottom line is turbochargers are still the power adder of choice for most racers, but the tide is turning.

“Turbo cars may still be running the quickest times,” says Kempf. “But it seems that, more and more, the blower cars are winning the races. If we can get the boost we need from a blower, I’m ready for the change.”

A new generation of centrifugal superchargers is challenging the boost capability of turbochargers that have long ruled Outlaw-type drag racing, offering comparable boost capability with less plumbing complexity and reduced stress on the transmission, particularly when staging.

LS Performance Potential

Simply put, the performance potential of a boosted LS engine is almost unlimited. Whether simply adding a bolt-on kit to an otherwise unmodified engine or building an engine from the ground up to support a larger horsepower goal, the parts are available to do it all, including dedicated performance cylinder blocks designed to withstand nearly 30 psi of turbocharged boost and more than 2,000 hp.

Realistically, most enthusiasts and builders are aiming for something more modest in a street-driven or street/strip car. But the already high power levels of stock LS-powered vehicles (from the 305 hp of the 1998–2002 LS1-powered F-Body cars to the 505 hp of the LS7-powered Corvette Z06) means the return on a supercharger or turbocharger investment will be impressive.

In most cases, a standard street-based bolt-on supercharger or turbocharger kit adds approximately 100 to 125 hp. Bolt-on twin-turbo systems can approach or exceed 200-hp gains, but extreme care must be taken with tuning on an engine with a stock rotating assembly, as factory-installed cast pistons and rods don’t stand up long if detonation occurs, or even if there is excessive heat from a slightly lean air/fuel mixture.

In fact, when a forced-induction system is planned to exceed the stock engine’s output by more than about 150 hp, the builder should consider fortifying the engine with forged rotating parts and lower compression pistons.

Perhaps the ultimate demonstration of forced-induction LS power is the twin-turbocharged 1996 Impala SS built by GM Performance Parts. Its 400-ci LSX iron-block engine produces more than 2,000 hp with help from a pair of 88-mm turbos.

Cast Rotating Parts: Pushing the Factory Parts’ Envelope

Production LS engines (except the C6 ZR1’s LS9, the Gen V Camaro ZL1, and the Cadillac CTS-V’s LSA) weren’t designed for supercharging. And while the basic engine design has proven to be remarkably durable, the cylinder pressure generated by a supercharger or a turbocharger takes its toll on the engine’s internal components.

The only LS engine from the factory to come with forged pistons was the LS9. All of the rest (the LS7 and LSA included) use hypereutectic (cast) aluminum pistons. Powdered metal rods and a mix of cast and forged crankshafts are used as well, but the bottom line is the basic rotating assembly was not designed for the rigors of forced induction.

That’s not to say the factory parts don’t withstand forced induction. In fact, typical bolt-on blower and turbo kits survive very well with otherwise-stock engines. Generally speaking, however, bolt-on kits deliver less than 15 pounds of boost and vehicles that are primarily street driven don’t see extended use at wide open throttle.

When tuned properly, stock engines survive admirably. It’s when the boost level is turned up and the vehicle’s use sees increased racing duty that the longevity of the factory internal components is reduced. (See chapters 8 and 9 for engine-building guidelines, including the use of forged rotating components.)

Compression Ratio and Recommended Boost Limits

Another performance limitation when using forced induction on an LS engine with stock internal components is the high compression ratio. The engines in most popular LS-powered performance vehicles, from the LS1-powered F-Bodies to the LS7-powered Corvette Z06 have comparatively high compression ratios that range from 9.0 to 11.0:1.

When building a forced-induction combination that’s planned to exceed the performance level of a bolt-on kit with relatively mild boost, the investment in stronger rotating parts must be made. Most LS production engines don’t come with a forged crankshaft, rods, or pistons. They’re must-have items to ensure engine strength and durability.

A high compression ratio supports greater power output but increases the tendency for the engine-damaging conditions of detonation and preignition. Those conditions can be especially hard on the factory-installed cast pistons. As a result, the boost pressure on otherwise-stock engines should be limited to prevent damage and ensure performance longevity.

Most intercooled/charge-cooled, street-intended bolt-on supercharger and turbo kits deliver between 5 and 8 pounds of boost, and that’s sufficient for stock-engine vehicles. Some kits push toward 10 pounds (with turbo kits easily tuned to deliver much more), but anything more than about 12 pounds is pushing the boundary of engine safety. Enthusiasts and builders seeking more than about 12 pounds of boost from an LS engine should consider rebuilding it with forged rotating parts and a lower compression ratio of approximately 9.0 to 9.5:1.

Because production LS engines have relatively high compression ratios, extreme care must be taken to avoid detonation with superchargers and turbo systems. Bolt-on kits can be tuned to minimize the risk, but lower-compression pistons should be used when building an engine for greater power and higher boost levels.

Production Engine Compression Ratios
GEN III Engines
LS1 5.7L	10.1:1
LS6 5.7L	10.5:1
Vortec 5.3L (early trucks, including SSR)	9.5:1
Vortec 5.3L (later trucks)	9.9:1
Vortec 4.8L (truck applications)	9.1:1
GEN IV Engines
LS2 6.0L	10.9:1
LS3 6.2L	10.7:1
L99 6.2L (2010+ Camaro SS with Active Fuel Management)	10.4:1
LS4 (front-drive application)	10.1:1
LS7 7.0L	11.0:1
LS9 6.2L	9.1:1
LSA 6.2L	9.0:1
L92/L94/L9H 6.2L	10.5:1
Vortec 6.0L (various truck applications)	9.4, 9.6, and 10.8:1

Crankcase Ventilation

LS engines have a tendency toward blowby, where combustion gases and engine oil slip past the piston rings. The condition is exacerbated with forced induction, which can push a considerable amount of oil out the engine in a relatively short period; and the factory positive crankcase ventilation (PCV) system may not accommodate the additional pressure introduced by a turbocharger or a supercharger.

Some turbo and supercharger kits include replacement valve cover breathers, but they may not be sufficient in some cases. Installing larger breathers and possibly a catch can for oil may be required. In racing applications, the engine may benefit from a vacuum pump. However, the bottom line for builders is: be prepared for blowby.

Importance of Tuning and Avoiding Detonation

The previous sections that described boost levels, compression ratios, and forged engine components are all tied together by the importance of proper tuning of a forced-induction engine. Without it, even the strongest engine parts don’t last long under pressure if the air/fuel ratio is too lean or the engine is prone to detonation.

Detonation is the uncontrolled combustion that is typically caused by excessive heat in the cylinders, whether through a too-lean air/fuel mixture or other factors. The added heat generated by a blower or a turbo system makes forced-induction engines extremely susceptible to detonation, particularly under high load and higher boost levels.

A high compression ratio can also contribute to detonation, making it important that an otherwise-stock engine (especially an LS engine with its comparatively high compression ratio) is tuned properly to prevent detonation at all costs. Many builders are adept at installing the hardware of a turbocharger or supercharger system but don’t have the knowledge to upload the proper software when it comes to the engine controller. Anyone who isn’t proficient at tuning should leave it to someone who is (see chapter 7 for more tuning details).

Enhanced crankcase ventilation is essential in a boosted LS engine to quell crankcase blowby. In some cases, a catch can for oil may be required in addition to conventional breathers.

Charge Cooling/Intercooling

To put it simply, compressing air, as superchargers and turbochargers do, generates heat. In the engine, that means an increase in the inlet air’s (the boosted air that enters the engine) temperature of up to 200°F at 8 pounds of boost.

Hotter inlet air significantly reduces the effectiveness of the boosted air charge because it is less dense than cooler air. It also makes the engine more susceptible to detonation. A charge-cooling system, commonly called an intercooler, combats the effects of a hotter cooling system by forcing the air charge through a radiator-like device to reduce its temperature before it enters the engine at the throttle body. Because of the concern for detonation on LS engines with their relatively high compression ratios, almost all bolt-on supercharger and turbocharger kits include a charge cooler.

A charge-cooling system not only helps deliver more power through a denser intake charge but it is especially important on street-driven cars to stave off the engine-damaging effects of detonation with the high compression ratio of internally stock engines.

There are two basic types of charge coolers: air-to-air and liquid-to-air (also known as water-to-air). With an air-to-air intercooler, the boosted air charge simply blows through a “radiator,” where air rushing over the fins provides the cooling effect. A liquid-to-air system is more like a conventional radiator and includes a dedicated circuit of coolant (typically a 50–50 mix of antifreeze and water, just as in the engine’s radiator).

Generally speaking, a liquid-to-air charge-cooling system is more effective on higher-powered, street-engine combinations and racing combinations. It requires a separate cooling circuit, a coolant reservoir, and an electric-driven water pump.

Auxiliary Instruments

Keeping tabs on a force-inducted engine usually requires instruments that aren’t found in a vehicle’s standard gauge cluster. That means adding auxiliary gauges, and it’s a process that’s been done as long as hot rodders have been experimenting with power adders (since the 1940s and 1950s).

A quick scan of any performance parts catalog or website reveals dozens of different instruments, all seemingly vital to monitoring engine performance. But when it comes down to it, there are four gauges that are more important than the rest when used with supercharged and turbocharged engines.

Boost Gauge: A simple instrument to install by tapping into a vacuum source on the engine (usually by inserting a T-fitting where a vacuum hose is located on the intake manifold), it delivers a reading of positive manifold pressure when the supercharger or the turbocharger is generating boost. For most bolt-on supercharger and turbo systems, a gauge with a maximum range of 15 to 20 pounds of boost is adequate. Higher-boost gauges are available in 30- and 60-pound ranges.

Fuel Pressure Gauge: More important than the boost gauge is the fuel pressure gauge, which can provide a glimpse of inadequate fuel pressure and give the driver the opportunity to shut off the engine before a lean-out condition causes engine damage. An electric gauge is preferred for the higher fuel pressure of the electronically controlled injection systems found on LS engines. Because of the obvious safety concerns of tapping into the fuel system to draw the pressure reading, high-quality fittings and lines (including braided steel) must be used. Typically, the fuel system is tapped at the Schrader valve on the fuel rail or the fuel pressure regulator.

Auxiliary gauges complement the forced-induction system, keeping tabs on the boost, fuel pressure, and more.

Air/Fuel Ratio Gauge: Like the fuel pressure gauge, an air/fuel ratio (AFR) gauge can indicate a potentially damaging lean condition, but it is also helpful for monitoring the mixture to optimize tuning across the RPM band. Installation is fairly simple. It simply connects to the wiring of the oxygen sensors, whether factory-style narrowband or wideband sensors. It is possible to split the connection so at the flick of a switch, the AFR from each cylinder bank is read separately. Or for the ultimate in engine minding, a pair of AFR gauges can be used to simultaneously monitor each cylinder bank.

Pyrometer (exhaust-gas temperature gauge): The pyrometer is more useful with turbocharged engines, where the exhaust temperatures can be extremely high. Excessively high exhaust temperature can indicate a lean fuel condition, restricted engine air supply, or a damaged turbocharger. Installation involves connecting the gauge to a thermocouple that is mounted on the exhaust manifold ahead of the turbocharger. Pyrometers are typically offered with maximum ranges of 1,200 to 2,400°F. Lower-range gauges should suffice for most low- and moderate-boost turbo engines.

Forced-Induction Terms

Throughout this book, a number of terms are used to describe or support specific characteristics, components, and performance related to forced induction. Reviewing them through the definitions below will enhance your comprehension of the following chapters.

Adiabatic Efficiency: The amount of heat generated when air is compressed by the supercharger or turbocharger in relation to the amount of the air compressed. Superchargers and turbochargers typically have adiabatic efficiency ratings of 50 to 75 percent. A 100-percent efficiency rate equals no heat generated during compression.

Air Compressor: With either a supercharger or a turbocharger, it is the fanlike device that blows pressurized air into the engine’s air inlet.

Air Density Ratio: The difference between the denser air under boost and the outside air.

Air/Fuel Ratio (AFR): The mass difference between air and fuel during the combustion process. For gasoline engines, the optimal (see Stoichiometric) AFR is 14.7:1, or 14.7 times the mass in air to fuel. A higher number indicates a leaner mix (lower fuel content in the mix). A lower AFR number indicates a richer mix (one with greater fuel content). A lean mixture (one with a higher air/fuel ratio) can lead to detonation.

Blow-off Valve: A vacuum-actuated valve that releases excess boost pressure in the intake system of a supercharged or a turbocharged engine when the throttle is lifted or closed. The excess air pressure is released to the atmosphere.

Boost: The pressure of compressed air at the intake manifold that is generated by the supercharger or turbocharger. It is generally measured in pounds per square inch (psi) or bar. A 1-bar measure is equal to 14.7 psi.

Boost Controller: A device used to limit the air pressure that acts upon a turbocharger’s wastegate actuator to control the maximum boost at the engine. It can be a mechanically or electronically controlled device.

Bypass Valve: Similar to a blow-off valve, it is a vacuum-actuated valve designed to release excess boost pressure in the intake system of a turbocharged car when the throttle is lifted or closed. The air pressure is recirculated back into the nonpressurized end of the intake (before the turbo) but after the mass airflow sensor.

Charge Cooler: A radiator-like device that is used to dissipate or reduce some of the heat generated by the compression of the boosted air charge, enabling greater power and/or helping reduce or eliminate the tendency for detonation.

Detonation: Abnormal and uncontrolled flame activity in the combustion chamber that can cause engine damage, typically due to excessive heat. In a forced-induction engine, detonation is generally caused by a lean fuel mixture, too-high compression, improper tuning, or a combination of all three.

Heat Exchanger: The radiator-like part of a charge-cooling system.

Intercooler: See Charge Cooler.

Preignition: Similar to detonation, preignition is a potentially catastrophic condition whereby heat retained in the cylinder causes the spark plug to act like a diesel engine’s glow plug, igniting the incoming fuel charge before the piston reaches the top of its stroke. A cooler air charge can reduce the chance of preignition.

Stoichiometric Combustion: The ideal combustion process that completely burns the air/fuel mixture. Generally speaking, an AFR of 14.7:1 in a gasoline engine delivers Stoichiometric combustion (see Air/Fuel Ratio).

Turbine: The part of a turbocharger that is acted upon by the engine’s exhaust gases. Hot exhaust gases flow into the turbine, spinning it. In turn, the turbine spins the corresponding air compressor that blows fresh air into the engine.

Turbo Lag: The time difference between the application of the throttle and the power boost delivered by the turbocharger.

Wastegate: A boost-pressure-activated valve that allows excessive exhaust gas to bypass the turbocharger’s turbine. It is used to control boost pressure.

Real-World Project: Larry Dye’s 1,300-hp Gen V Camaro SS

“Small” isn’t part of a Texan’s vocabulary, so it should come as no surprise that when Gen V Camaro enthusiast Larry Dye wanted to hit the street and strip with something that would make a big impression, he didn’t bother messing around with the stock 6.2L LS3 for very long. He went with a force-fed LS-based 427 engine boosted by a couple of turbos and a 200-shot of nitrous waiting in the wings for that final push over the edge.

“It makes about 1,300 horsepower to the tires,” says Dye. “That may seem like overkill for a street/strip car, but it actually is drivable. You can drive it on the street comfortably or drive it to the track, change the tires and rip off a few 9-second ETs.”

What’s even more intriguing is the deceptive appearance and street-driving demeanor of the car. Apart from the roll bar inside, the interior is pretty much stock; at least, it’s not a gutted, tin-covered race car cabin. The same goes for the exterior. There are no wings, extraneous scoops, or other race car accoutrements.

“The understated appearance wasn’t necessarily intentional, because I didn’t set out to build a dedicated race car at first. I just wanted a fast street car,” says Dye. “The car evolved from a 650-horsepower supercharged combination with the original LS3 to a twin-turbo system on the LS3, which wasn’t up to the power and punched a rod through the aluminum block. It was then that I doubled down with a new builder with a built-for-bear LSX engine, but we found the limits of that block before it was recently improved. Now, we’re using a Dart LS Next block for the foundation.”

Larry Dye’s twin-turbocharged street/strip Camaro SS runs low-9-second ETs.

With 23 pounds of boost feeding the engine in Larry Dye’s Camaro, a sheet metal intake is used for safety instead of a factory-style plastic intake that could crack or shatter. The engine makes 1,300 hp with a pair of Precision Turbo & Engine ball-bearing turbos.

Along with the Dart block, there’s a Callies Magnum forged-steel crankshaft (4.000-inch stroke), a set of Wiseco pistons (4.125-inch bores), and 6.125-inch-long Callies Ultra H-beam connecting rods. There’s also a custom-grind COMP Cams camshaft. Atop the rotating assembly sits a pair of LSX-LS7 six-bolt, high-flow ported cylinder heads delivering 410 cfm worth of airflow on the intake side and 275 cfm on the exhaust side (at 0.600-inch lift). The heads feature Del West 2.20-inch titanium intake valves and Manley Inconel exhaust valves measuring 1.61 inches, all complemented by Manley 0.700-inch-lift dual-coil valve springs and COMP

Cams tool steel retainers. They are secured to the block via ARP 2000 head studs.

It’s a solid, durable long-block that absorbs 23 pounds of boost generated by a pair of Precision Turbo & Engine hybrid 62/66-mm ball-bearing turbochargers. They blow into a Precision Metal Craft sheet metal intake manifold, where the pressurized air charge is mixed with fuel delivered via 140-lbs/hr injectors mounted in Aeromotive LS7 fuel rails. There are a couple of TiAL Q-series blow-off valves, too, to relieve pressure, along with an HKS EVC-V boost controller. The injectors are fed by a Weldon fuel pump in addition to the output from the OEM fuel pump.

The car makes this power on a street-friendly 93-octane tune, though they do use just a hint of water/methanol injection (from a custom-fabricated tank in the trunk) as a safety factor to help keep the charge temps down in the blistering Houston summer heat.

It’s a combination that has proven durable on the street and strip, proving there’s virtually no limit to boosted LS performance.