Engine Performance: System: Turbocharger: Operation
Turbine impeller of turbocharger is driven by exhaust gases expelled from cylinder combustion chambers. At idle, no pressurization of intake air takes place and engine operates like a normally aspirated engine.
With engine under partial load, throttle valve opens and more air/fuel mixture is drawn into combustion chambers. Speed and volume of exhaust gases also increase. Increased amount of exhaust gases turn turbine impeller at a higher RPM. If boost pressure of intake air is 11 psi (0.8 kg/cm2 ) or higher will signal the EGI control unit of over boost and will flash indicator light.
Compressor impeller turns at same RPM as turbine impeller because they are mounted to same shaft. Increased RPM of compressor impeller boosts pressure of intake air. With engine under full load, exhaust gases are at maximum pressure, which increases RPM of turbine and compressor impellers to an extremely high speed.