Engine Performance: System: Turbocharger: Operation

The turbine impeller of the turbocharger is driven by the exhaust gases expelled from the cylinder combustion chambers. At idle speeds the engine operates like a normally aspirated engine.

As engine speed increases with opening of the throttle valve, the amount of exhaust gas increases. This leads to an increase in the rotational speed of the turbine. Turbine speed may increase up to 130,000 RPM.

The turbocharger is equipped with a wastegate to prevent engine damage from excessive boost pressure. Below 6.4 psi (.45 kg/cm² ) the wastegate valve is closed so all exhaust gas is directed through the turbine. At the specified pressure, the wastegate diverts exhaust gases around the turbine. The wastegate valve controller diaphragm is operated by an air pressure signal from the intake manifold. The air relief valve is designed to relieve air pressure at 7.5 psi (.53 kg/cm² ).

The turbocharger is lubricated by engine oil. Full floating type bearings are used to form desirable lubrication films on bearing surfaces during operation. Lubricating oil is also essential in cooling the turbocharger to prevent bearing failure.

The turbocharger is water cooled. Coolant flows through a drain hose from cylinder head through a pipe to turbocharger bearing housing. After bearing housing is cooled, coolant flows into thermostat housing in intake manifold.