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. Gunmetal/Chrome, 40mm valve, adjustable, funnel outlet, 100-400hp range, BOV gasket, nuts & bolts