Maximizing the performance of a supercharged or turbocharged vehicle includes more than the power adder itself. A number of supporting components in the powertrain and chassis require upgrades or attention to not only realize the full horsepower potential of the forced-induction system, but to ensure long-term durability by supporting the greater load imposed by the blower or turbo.
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Headers and Exhaust System
Simply put, a bolt-on blower or turbo kit won’t deliver as much power when breathing through the stock exhaust system. Obviously, the stock exhaust system is designed to minimize the sound level across the RPM band, but supercharged engines perform better with the least restrictions. Turbocharged systems, on the other hand, need a little backpressure for optimal performance, but not an excessive amount. Also, the very nature of how turbochargers are installed in the exhaust stream requires changes to the exhaust system.
The elements of the exhaust system discussed here include the exhaust manifolds and exhaust system after the catalytic converter, but the decisions for upgrading them aren’t necessarily as obvious as they seem. Installing headers with a catback exhaust system (one that bolts on after the catalytic converter to ensure emissions compliance) is often the best way to maximize exhaust flow, but not all headers provide a commensurate return on investment.
On most LS-powered exhaust systems, the cast-iron exhaust manifolds flow quite well, with the merge-style manifolds of the LS7 and LS9 engines being particularly good. Adding conventional “shorty” headers (those with shorter runners that bolt up within the stock exhaust system) may provide only a marginal airflow increase over the stock manifolds. Long-tube headers provide unquestionably greater flow than stock manifolds and shorty headers, but they also require additional system changes, including the possibility of new catalytic converters, due to the repositioning of the header outlets. Also, long-tube headers may not be legal in all areas.
The header option for turbocharged vehicles is mostly negated by the fact that they require either thick, cast-iron manifolds when the turbos are mounted directly to them, or one-off fabricated manifolds to accommodate a custom mounting position of the turbochargers.
Fortunately, superchargers and turbo systems don’t necessarily increase the sound level of the engine by themselves, so adding a typical cat-back exhaust system does not adversely affect the sound quality of the vehicle. In fact, with a Roots-type or twin-screw blower, it may even be quieter at idle and low speeds. Of course, a lower-restriction exhaust system will be louder at higher RPM and wide-open throttle, but that would be the case for a non-blown vehicle, too.
The bottom line is a blower or turbo system should be complemented by a lower-restriction exhaust system to realize more power on the street. The cat-back system should be the priority over headers, too. There are countless aftermarket cat-back exhaust systems for all LS-powered vehicles, so finding one isn’t a problem. Bolt-on headers, however, can be an issue for some vehicles, as they are not available for all LS-powered vehicles. The majority of the popular models have headers available, however.
For the enthusiast having a forced-induction system installed by a professional tuning shop, it is ultimately more cost effective and time effective to have the exhaust system installed as part of the entire project.
Real-World Project: Installing a Cat-Back Exhaust System
The installation of a bolt-on catback exhaust system is relatively easy, but can require the assistance of professionals or at least professional tools. Later-model LS-powered vehicles, such as the Pontiac G8 GT/GXP (and its Holden/Vauxhall cousins) and Chevy Camaro, are equipped from the factory with very large, completely welded exhaust systems. On the fifth-generation Camaro, for example, the exhaust system after the catalytic converter comes out of the car as a single component that is more than 9 feet long. It was replaced with a Corsa system comprised of multiple (and more manageable) components.
Although the basic procedures involved with this exhaust swap are easily handled by the do-it-yourselfer, the length of the stock system, along with the leverage required to remove hard-to-reach muffler hangers, means the job should almost certainly be done with the vehicle on a lift. There just isn’t enough room to maneuver with the jack stands and ramps found in most home garages.
As mentioned in the previous section, taking the cost and labor for a cat-back exhaust system into consideration when committing to an entire blower/turbo installation at a professional shop is probably the best option for most enthusiasts. The following is the installation of a Corsa cat-back exhaust system on a 2010 Camaro SS, which is similar to the Pontiac G8 and Holden Commodore. And, in general, the steps outlined are similar for most bolt-on exhaust systems on most LS-powered vehicles.
Along with boost comes heat that promotes detonation and saps horsepower. So, the cooling system of a force-inducted car is a crucial component in ensuring consistent, longterm performance. The radiator and cooling fan(s) are the items to address, as the stock water pump is adequate for street-based vehicles with supercharger and turbo systems.
For most LS-powered vehicles, the standard radiator provides sufficient cooling capacity for bolt-on blower kits and mild-boost turbo systems. For all street vehicles with forced-induction systems that exceed 10 pounds of boost, larger-capacity radiators should be considered.
The electric cooling-fan assembly on performance-oriented vehicles, such as fourth-generation F-cars, Corvettes, G8/Commodores, and fifth-generation Camaros is also adequate for most street-based vehicles. Earlier truck-based LS vehicles, such as pickups, SUVs, and the TrailBlazer SS, benefit from cooling-fan assemblies that convert engine-driven fans into more controllable electric-fan systems. Popular swaps include the efficient fans from C6 Corvettes and the twin-fan arrangement from LS1- powered fourth-generation F-cars, particularly TrailBlazers.
A number of aftermarket sources offer electric fan conversion kits that include all of the necessary parts and wire harnesses. Such a conversion requires a tuning adjustment in the engine controller to not only activate the fans, but prevent the “Check Engine” light from illuminating.
The Tremec 6-speed manual transmissions that have been offered with select production vehicles, such as the F-car, Corvette, and GTO/ Monaro, hold up well to bolt-on supercharger and turbocharger kits on cars primarily driven on the street. Vehicles that see considerable time on the drag strip or road course benefit from upgrades to strengthen internal components, such as swapping the shift forks and synchronizer keys with heavier-duty parts.
Additionally, higher-capacity, dualfriction clutches work well to prevent slippage and should be considered at the time of the supercharger installation, particularly if the vehicle has more than about 40,000 miles on the odometer. A stronger flywheel is also a wise consideration on high-power vehicles, as stock ones can break under high load.
When it comes to automatic transmissions, the stock Hydra-Matic automatic transmissions, which came equipped on the vast majority of LS-powered vehicles, can quickly strain the far edge of their capability envelope when a blower or turbo is added to the powertrain. Those transmissions are manufactured and electronically controlled to perform within a limited performance range and the 100-plus horsepower that is added to the drivetrain with a turbocharger or supercharger quickly exceeds the automatic transmission’s torque capacity. The lifespan of the transmission diminishes even quicker if the vehicle is regularly drag raced.
A number of performance transmission companies offer upgraded versions and kits for GM’s electronically controlled transmissions. As with manual transmissions, the majority of upgrades include replacing internal components with stronger, heavier-duty components. Indiana-based RPM Transmissions offers a range of upgrade options for the popular 4L60/4L65 transmissions and 6-speeds that include stronger clutch packs, hardened output shafts, and other strengthened components.
Along with strengthening the transmission (manual or automatic) to stand up to forced induction, another consideration when upgrading the transmission is altering the gearing to better match the power delivery of the supercharger or turbocharger. The same goes for the torque converter in automatic transmission vehicles. This is more of a concern for supercharged vehicles, where additional power is being made at even the lowest RPM levels. Stock transmissions, particularly GM’s automatics, have relatively “short” (numerically low) first gears that provide energetic launches in stock form, but are overkill with a power adder. A taller first gear (and equally matched gear pack) provides smoother, more controlled launches on the street and strip.
As for torque converters, there’s not enough room in this chapter to give advice on selecting the most appropriate one. Your best bet is contact the tech department of a trusted, recommended performance converter manufacturer and discuss the type of power adder, along with the vehicle’s intended use, to receive a professional recommendation.
The rear axle on full-size pickups and SUVs are strong enough for most bolt-on blower and turbo kits, but those of other LS-powered vehicles are on the edge of their maximum load capacity when used with forced induction.
Generally speaking, the stock solid (Salisbury-type) rear axle of fourth-generation F-cars, TrailBlazers, SSRs, etc., should hold up to most street use and mild to moderate drag racing. More regular racing and the use of slicks or drag radial-type street tires hastens the demise of a stock axle, as the high load that comes with strong traction is usually the culprit of a broken axle. In a very real sense, the axle in a car with street tires that spends more time spinning its tires than yanking its way to 1.2- second 60-foot times lasts longer.
Stronger axle shafts and differential units are the cure for most vehicles, while replacing the stock axle assembly with a stronger, racingstyle assembly from aftermarket manufacturers such as Strange or Currie Enterprises is recommended for higher-powered vehicles and those expected to spend more time at the race track. Convenient, directswap kits are offered for popular applications, such as the fourthgeneration F-car (see “Real-World Project: F-Car Axle Swap”).
Independent Axle Options Although surprisingly robust in stock form, the basic design of an independent rear axle system is inherently weaker than a solid axle when it comes to the strains of drag racing and very high power on the street. For owners of a GTO/Monaro, G8/Commodore, Cadillac CTS, and fifth-generation Camaro, there’s a well-established aftermarket industry catering to GM’s independently sprung rear-drive cars. Stronger CV shafts, axle stubs, driveshafts, differential units, and more are available, along with chassis and suspension components designed to quell wheel hop and other launch issues. Floridabased BMR Fabrication has one of the largest selections of these parts.
Solid Axle Conversion
On vehicles intended for regular use on the drag strip, the replacement of a factory independent axle, such as the one found on the Pontiac GTO, G8, and fifth-generation Camaro, with a solid axle is a wise consideration. Regardless of the strength of the differential or axle shafts, an independent-rearsuspension design simply doesn’t offer the strength required for the load put upon it by repeated fullthrottle launches, especially the hard-biting launches that come with using racing slicks or drag radials.
Currently, there aren’t any direct-swap solid-axle conversions kits to recommend, but several GTO racers have adapted kits for fourthgeneration F-cars. Similar adaptations can be applied to the G8, Camaro, and even Cadillac CTS.
Real-World Project: F-Car Axle Swap
In LS vehicles with solid rear axles, primarily fourth-generation F-cars and trucks, those axles may not stand up to the torque from a high-boost, high-horsepower engine combination. The F-body axle, for example, is a relatively mild 10-bolt/ 7.5-inch design that is only slightly stronger than similar axles used on countless low-power sedans of the 1980s.
Indeed, for most serious street vehicles and race cars, GM axles aren’t always the first choice. Nine times out of 10, there’s a Fordderived 9-inch tucked between the rear wheels. Of course, most highperformance 9-inch rear ends these days share only the design of the Ford axle—all the parts are newly manufactured. The 9-inch design has proven to be extremely durable, but there is another strong, performance-minded axle option in the Dana 60 design.
As with most new 9-inch axles, the late-model Dana 60 is completely manufactured by another company. In this case it’s Strange Engineering, called the S60. With the popularity and proven track record of the 9-inch, it is logical to ask, “Why venture into uncharted territory with the Dana 60?” For one thing, it is extremely durable. Strange Engineering says the larger, 9.75-inch Dana 60 is about equal in strength to a Ford 9-inch, but offers that strength at a lower cost. Certainly, cost is a factor for most enthusiasts, so strength for less cash is an enticing combination.
Strange says the S60 axle weighs only about 25 pounds more than a comparably built aftermarket 12-bolt setup. And while the individual components for the axle can be purchased separately, Strange offers the S60 in a complete, bolt-it-in combination with 35-spline axles for many GM vehicles, including the fourthgeneration F-car. The following is the installation of an S60 axle assembly into a fourth-generation Camaro. For this project, the complete package included the S60 case and axle tubes with spring perches already welded to them. Because almost no two enthusiasts’ combinations are alike, here’s a rundown of what the project axle assembly included:
- S60 housing
- 3-inch axle tubes and end housings for late-model F-cars (with spring perches installed)
- Power-Lok locking differential
- 3.73-ratio ring-and-pinion
- 35-spline S/T inductionhardened axles
- Aluminum rear-end cover
Because Strange’s custom S60 case is designed specifically for this application (it’s not a cleaned-up, old Mopar part), the F-car’s suspension components bolt right up to it. The only considerable detail to work out with the axle swap was the driveshaft. Because the S60’s pinion is longer than the 10-bolt’s, a shorter driveshaft was required. So, after careful measurements were taken with the axle installed, a custom metal-matrix shaft from Strange was ordered to fit. It bolted up without a hitch and the Camaro project car was again mobile—and ready to withstand the stress of a high-boost blower engine.
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 began experimenting with power adders in 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 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 leanout 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.
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 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 degrees F. Lower-range gauges should suffice for most low- and moderateboost turbo engines.
Written by Barry Kluczyk and Posted with Permission of CarTechBooks