Race N75 Frequency Valve
Audi B5 A4 Quattro 1.8T 

The N75 is the VW/Audi part identification number for the wastegate by-pass regulator valve. This valve is responsible for controlling the movement of the pneumatic actuator which drives the wastegate. The wastegate is an internal valve in the turbo-charger which controls the amount of exhaust gas that flows over the turbo impeller generating boost. Under normal operating conditions the engine's ECU sends signals to the N75 valve asking it to open or close which adds or reduces pressure on the wastegate actuator which results in more or less boost. The ECS RACE N75 valve modifies the normal operating parameters of the original N75 valve by delaying the speed at which these ECU signals are interpreted. The result is a higher initial peak boost and an elevated boost curve which tapers back to stock/chipped levels over the engines rev range. Average boost gains are 1-3psi over the rev band.