Blitz VD Polished Dump Valve Kit - 70183 - Impreza V1 & 2Blitz Venturi Drive Super Sound Blow Off Valve Release Type The all new ribbed main body dissipates heat more effectively and the venturi shaped funnel creates a sharp dynamic sound. Venturi Drive dump valves also feature "Dual Drive" for maximum response, a small port for low boost and a larger port for high boost. Manufactured from die cast polished aluminium with a brass piston and a rubber diaphragm, meaning they can easily cope with boost