Variable Induction System: Description and Operation

ACIS System:

PURPOSE
The acoustic control induction system (ACIS) controls the effective length of the intake manifold runners.

THEORY
Air inside the intake system does not flow at a constant speed, but pulsates. Each pulsation consists of a low and high pressure condition. If pressure directly above and intake valve is high immediately before the valve closes, a larger amount of air is drawn into the cylinder. The result is increased torque.

Modifying intake runner length maximizes this affect by allowing the ECM to maintain high relative pressure at the intake valve over a wide range of operating conditions.


SYSTEM COMPONENTS
The system consists of a two chambered intake manifold, a vacuum controlled passage between the chambers, an ECM operated solenoid and a vacuum tank to maintain a steady source of vacuum.


Actuator
The actuator is a vacuum operated unit that physically opens the intake air control valve (IACV). Located under the intake manifold, based on ECM vacuum control it opens and closes the IACV based on engine demand. When vacuum is present at the actuator the IACV closes the center passage, effectively lengthening the intake runner.

Vacuum Solenoid Valve (VSV)
The VSV is a two port vented vacuum solenoid. With no power applied, vacuum is shut off and atmospheric pressure is allowed to the actuator. When energized, vacuum passes through the solenoid, to the actuator.

Vacuum Tank
To maintain a steady vacuum supply, a vacuum tank is mounted under the intake manifold. A check valve prevents vacuum from releasing during low intake manifold vacuum conditions.

ACIS System Operation:

OPERATION
The IACV is opened and closed based on engine demand and speed. Refer to chart for operating conditions.