Greddy Type-RS Blow Off Valve Kit - VW Golf 1.8T 98-05. If the throttle plate is closed while engine is making boost, the compressed air will return to the compressor housing which causes "compressor surge" and also damages the turbine shaft. In the same condition, the GReddy Blow Off Valve will release the copressed air from the charge pipe to protect the turbocharger from the pressure spike and also gives quicker boost recovery. By modifying the vaccum line routing, it can also be used as a Relief Valve.