Variable Induction System: Description and Operation

PURPOSE
The Variable Intake Control System (VICS) changes the effective length of intake manifold runners, taking advantage of high and low pressure oscillations to improve volumetric efficiency at different engine speeds.

LOCATION
Shutter valves are in dynamic chamber.

OPERATION
Opening and closing of the intake valves causes areas of high and low pressure to oscillate through the intake manifold at different harmonic frequencies, depending on engine speed. VICS changes the effective length of intake manifold runners, taking advantage of these oscillations to improve volumetric efficiency at different engine speeds. At low and mid-range engine speeds, oscillation frequency is low and shutter valves are closed. Intake air takes a longer path to the cylinders. At high speeds, oscillation frequency is higher. Shutter valves open and intake air takes a shorter path through the manifold. This synchronizes intake valve opening with the occurance of a high pressure area behind each valve. When an intake valve opens, high pressure air rushes into the cylinder followed by high velocity air from the intake runner. This "packs" cylinders with air/fuel mixture, producing more torque across a broader rpm range.

When engine speed is below 4900 rpm, manifold vacuum is applied to the diaphragm, holding shutter valves closed. When engine speed exceeds 4900 rpm, the PCM de-energizes the vacuum solenoid valve. The manifold vacuum port is blocked and the shutter valve diaphragm is vented to atmosphere. The diaphragm spring extends, opening the shutter valves.