The Turbocharger FAQ

A turbocharger is an exhaust-driven turbine which drives a centrifugal compressor wheel. The compressor is located between the air filter and the intake manifold (or intercooler if so equipped), while the turbine is located between the exhaust manifold & muffler. The turbocharger's primary function is to compress the intake charge of air into the engine, thereby increasing horsepower.

The turbocharger is driven by exhaust energy which would otherwise be lost. A combination of exhaust heat and velocity are what transmit energy to the turbine. The turbine housing is constructed in such a way to take advantage of the exhaust energy and transform this into motion by spinning the turbine.

In most turbocharged engines, an intercooler is used. An intercooler is an air-to-air radiator. In compressing the intake charge, heat is generated. Above a certain boost level, the heat is so great as to cause engine-damaging detonation. The intercooler removes the heat from the intake charge to reduce detonation, and provide more power, as colder air is more dense, and means more horsepower.

Also most turbocharged engines incorporate a bypass valve. This valve's function is to relieve the excess pressure from the intake tract when the accelerator pedal is released. Otherwise the pressurized air would force its way back through the compressor, eventually leading to damage. This is known as compressor surge. Blowoff valves are popular as well, and perform the same function as a bypass valve, except instead of bleeding the air back into the air cleaner, the air is vented to the atmosphere, making a hissing sound.

It is very important, in any turbocharged engine, that the fuel system is operating properly, especially if more boost is to be run. Most engine failures involving turbos are due to detonation, brought on by the fuel system's inability to provide enough fuel to keep the air/fuel mixture at the proper levels. A wideband air/fuel mixture gauge is highly recommended for any modified turbo engine, as it will give a general indication of mixture.

Another enemy of the turbo engine is heat. Above 6 or so PSI of boost, a turbo engine cannot safely run more boost without an intercooler...thermal stresses on the engine are too great and the chance of detonation is too high. The cooler the intake charge, the more power can be made, and the longer the engine will run.

A turbocharger is a precision component. The bearings in the turbo are lubricated by engine oil, fed by oil pump pressure. In some cases the turbo is cooled by the engine cooling system. In either case, it is important to allow the turbo time to cool down, while the engine is sitll running - this ensures that the oil supply is maintained to the turbo, helping to eliminate the chance of oil coking, a phenomenon where the oil in the bearings is "baked" into an abrasive powder which is extremely harmful to the bearings.