ACIS (Acoustic Control Induction System)
The ACIS uses a bulkhead to divide the intake air chamber into two stages, with a intake air control valve in the
bulkhead to vary the effective length of the intake manifold. This increases the power output in all ranges from low
to high speeds.
This system is basically the same as the Intake Air Control System of the 7M–GE engine for the previous Toyota
VSV circuit for ACIS
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.