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
