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