Perrin Recirculating Blow off Valve Red 2002-2007 WRX / 2004-2021 STI

It is vital that a blow off valve for your WRX/STI recirculates the air back to the intake track to maintain proper air-fuel ratio and driveability between shifts. While this can be set up as a vent-to-atmosphere style blow off valve, we only recommend that on cars running aftermarket Speed Density type tuning (cars without mass airflow sensor). The unique design allows you to control the volume of air released when the blow off valve vents. Adjusting the volume of air helps maintain the perfect amount of boost in your system during shifts without causing compressor surge. Venting too little can damage the turbo, venting too much air can make the throttle less responsive. This adjustment is independent of the relief pressure allowing for a totally customizable blow off valve. The PERRIN Blow Off Valve cap features adjustable spring tension, which allows for an adjustment when the blow off valve vents. A looser setting will make it act smooth and more like stock. Setting it harder will