Engine Performance: System: Turbocharger: Operation: Notes
The turbine impeller of the turbocharger is driven by the exhaust gases expelled from the cylinder combustion chambers. At idle speeds there is no pressurization of intake air and the engine operates like a normally aspirated engine.
With engine under partial load, the throttle valve opens and more air/fuel mixture is drawn into the combustion chambers. The speed and volume of exhaust gases also increases which turns the turbine impeller at a faster RPM. The increased RPM of the compressor impeller boosts the pressure of the intake air.
With engine under full load, the exhaust gases are at maximum pressure and increase the RPM of the turbine and compressor impellers to an extremely high speed. The boost pressure of the intake air reaches a maximum.
When the pressure in the intake manifold reaches 8.4 psi (.59 kg/cm2 ), the diaphragm of the wastegate controller pushes against the linkage which opens the wastegate. Part of the exhaust gases are then routed directly into the main exhaust pipe, by-passing the turbine impeller. This prevents engine damage from excessive pressure.