This Perrin recirculating blow off valve for the 02-07 WRX & STI controls boost pressure that is built up by the turbo and vents it into the atmosphere when your Subaru is not under load (in between shifts). This prevents pressure from backing up into the compressor housing, causing the turbo impeller blade to rapidly stop or even worse, to spin backwards (compressor surge or backspin). Doing so can be potentially destructive to the turbine wheel, shaft, and turbo life in your WRX or STI.

The Perrin Recirculating Blow off Valve for the 02-07 WRX & STI is a direct bolt on for a simple install. Since this blow off valve recirculates air just like your stock blow off valve, you will not experience a rich condition between shifts, or hear a loud rush of air expelled. The Perrin Recirculating Blow off Valve is rated to hold 190 psi, so this blow off valve will never leak under high boost pressures.