Boost Pressure Influences:

Fuel Octane Rating

The high combustion pressures resulting from the increase in volumetric efficiency of turbocharging require a high-octane fuel. If the octane rating of the fuel is too low, what’s variously known as detonation, pinging, or spark knock will occur.

The end result of this knocking is damage to the engine. The ECM is programmed to retard ignition timing if detonation is detected. Excess spark knock will cause the ECM to enter a “Fail-Safe” mode wherein the boost pressure is reduced to the minimum value determined by the wastegate actuator.

Turbo Lag

The pressure of the exhaust gas is low at slower engine speeds. As the turbocharger uses exhaust energy to operate, it does not respond immediately when the throttle is opened.This is referred to as “turbo lag.”To overcome turbo lag, the turbocharging system and its controls are matched to each vehicle model, based on the vehicle’s specifications, features and the expected use of the vehicle.

By now, it should be pretty evident that the basic concept of the turbocharger is relatively simple, but attaching it to an engine, controlling its operation and getting the best results is quite complex. Subaru engines are perfectly matched to the turbocharging components for optimum function. The key factor to keeping them running at tip-top shape is following the correct maintenance procedures.