A turbocharger is an exhaust-driven air pump consisting of a pair of turbine wheels, not unlike pinwheels, on a single shaft. One turbine is positioned in the exhaust stream; when the engine revs, the exhaust makes it spin. This turns the second turbine, which is part of the intake system that directs air into the engine, and acts as a pump.
In order to develop boost, the engine must be working hard enough to produce significant exhaust pressure to spin the turbocharger. This results in “turbo lag” — the engine does not get a power boost at lower engine speeds, and it feels as if the car is hesitating instead of accelerating. Newer, more technologically advanced cars have less turbo lag than older cars. The advantage to using turbocharging to boost power is that when the turbo is active, the engine uses fuel, whether it be gasoline or diesel.
The benefit of turbocharging is that carmakers can use smaller, gas-sipping engines to get the same power and acceleration as a larger gas guzzling engine.