Viewed through the intake tube of the intercooler, the core of the intercooler is visible. It is vacuum operated so it only opens or closes. Under idle or light load condition (such as cruising down the freeway) the valve is held open by engine vacuum, bypassing boost. Once you stab the throttle, however, the valve closes and all the boost goes into the engine. This allows for the same or similar fuel mileage during normal cruising, good drivability, and no heat buildup. The amount of boost is dictated by the size of the supercharger pulley and engine rpm.