24. Here's a shot of the surge valve after it was installed. It is operated by vacuum or boost, and allows boost to be bypassed from the engine during normal riding conditions (idle, cruising) so that the bike delivers normal cruising feel, fuel economy and drivability. The surge valve is normally open. Once the engine senses load however and the engine goes from a normal vacuum situation to boost, the valve instantly closes and allows the boost into the throttle body. Upon deceleration, the valve opens again so that excess boost isn't backed up in the engine.