GReddy Blow Off Valves are easily adjustable to eliminate compressor surge and preventing premature boost leakage, while increasing boost response between shifts. Each valve is made of durable cast and billet aluminum frame and the valve to diaphragm ratio provides performance that cheap piston types cannot offer. The spring stiffness adjustment screw and the three different sizes give the GReddy user the option to match vehicles with mild upgrades to heavily tuned engines. There are many factors in matching a blow-off valve to an application, valve location, turbocharger size and pressure, but as a general rule of thumb, we recommend Type R for 260-450hp and the Stiff Spring Type R for over 400hp applications. Also available in easy to install kit form for many turbocharged vehicles.