Lag control - stopping the compressor from stalling against pressure build up when the main throttle is closed.
A pre-compressor throttle is used to lower the pressure before the compressor inlet, thus eﬀectively increasing the corrected mass ﬂow while keeping the actual mass ﬂow within its limits.
With conventional wastegated turbochargers or fixed geometry turbochargers (FGT), a turbine flow area cannot be adjusted during operation.
Knocking is abnormal combustion in which the air-fuel mixture ignites prematurely due to exposure to high temperature and pressure, creating an unwanted high-frequency noise. When the compression ratio is increased, the temperature at compression top dead center (TDC) also rises, increasing the probability of knocking.