Blow-off valves are essential to all turbocharged vehicles. The purpose of the BLITZ® Dual Drive Blow-off Valve is to relieve compressor surge without reducing compressor speed. It controls boost pressure that is built up by the turbo and vents it into the atmosphere when the car 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 and shaft. Repeated stress over time can cause eminent damage to the turbo charger and eventually lead to turbo failure. A blow-off valve is actuated by pressure changes only, ensuring quick valve responses and complete closures at idle. The BLITZ® Dual Drive Blow-off Valve not only improves performance and response, but also prolongs the life of the turbocharger. FEATURES DD (Dual Drive) for maximum response (small port for low boost + larger port for high boost) Includes mini SUS filter Urethane gasket to ensure complete seal Tension adjustable Available hard spring for high boost applications