Variable Induction System

DISA Schematic:

OPERATION
During low- and mid-range engine operation (<4,800 rpm), the DME control unit powers the solenoid valve open which applies reservoir vacuum to the vacuum motor. When activated, the vacuum motor causes the changeover valve to close creating a "long pipe" condition. As the engine approaches the high rpm range (>4,800 rpm), the long pipe advantage diminishes. When the changeover valve opens (>4,800 rpm), the engine breathing dynamics change due to the short RAM air pipes, creating higher output. The changeover valve closes below 4,760 rpm and opens above 4,800 rpm. The overlap of 80 rpm prevents the repeated open and closing of the valve.

The changeover valve is held in the "normally open" position by spring pressure. In the event of a system failure, the open flap allows full engine performance at high rpm for safety reasons.