Variable Induction System: Description and Operation

DISA Components:

PURPOSE
Variable length air intake pipes provide a measured supply of clean air which is mixed with injected fuel for combustion. Because of the ability to change intake pipe length, throttle response is improved and horsepower is increased over a broader rpm range.

CONSTRUCTION
DISA intake components include:

^ Primary chamber with dual intake pipes
^ Ram air manifold with changeover valve
^ Changeover valve actuating system

DISA Schematic:

OPERATION
During low- and mid-range engine operation (<4,800 rpm) the Digital Motor Electronic (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 and a significant increase in horsepower.

As the engine approaches the high rpm range (>4,800 rpm), the "long pipe" advantage diminishes. The DME control unit switches power off to the solenoid valve, removing vacuum to the vacuum motor and opening the changeover valve via spring pressure. When the changeover valve opens (>4,800 rpm), engine breathing dynamics change due to the short RAM air pipes, increasing power at higher rpm`s.

The changeover valve closes below 4,760 rpm and opens above 4,800 rpm. The overlap of 80 rpm prevents repeated opening 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.