The WRX Stealth FX is a direct bolt-on replacement blow-off valve for all late model Subaru WRX’s and STi’s from MY01 (MY02 in the U.S.) with no adaptors, extras or modifications required. Everything you need is supplied in the kit for quick and easy installation. Only the Stealth FX allows you to go from silent and unnoticeable to ear shattering in a matter of seconds! It is a little known fact that the late-model WRX factory blow-off valve is actually designed to leak at boost pressures exceeding the factory level. Replacing it noticeably improves throttle response, and is definitely recommended in applications where the boost has been raised. Standard Trumpet Driveby Stealth FX with standard trumpet, 15psi boost on a WRX, recorded from the side of the road. This sound is the same as a Mach 1. Standard Trumpet In-car Stealth FX with standard trumpet, 15psi boost on a WRX, recorded from inside the car. This sound is the same as a Mach 1. Standard trumpet free revving Stealth FX with standard trumpet, free revving the engine in neutral. Recorded from in front of the car. The advantages of this system, combined with GFB's other proven features are numerous... Fingertip control over how loud your shifts are! By simply turning the lower ring of the cap, you can adjust how much air is vented to the atmosphere or to the inlet, giving you complete 'noise control' over your shifts! For cars with sensitive air-flow meters, you can dial in the valve to eliminate common problems normally associated with aftermarket valves... and still get a great sound. No tools needed for spring adjustment. Spring adjustment is achieved via the chrome cap on the top of the valve. The unique adjustment mechanism is contained completely within the valve, meaning that the profile remains as low as possible, as the cap does not move up and down when adjusting. Unique piston seals achieve the best possible seal on both ends of the piston. Now, as well as our acetal piston seat, a low friction, lubricant-impregnated polymer piston ring is incorporated. This system is far more reliable than o-rings, which require frequent maintenance and replacement. Tight engine bays are NO problem! The vacuum nipple is free to rotate through 360 degrees to make fitting easier. The Stealth FX is available for: Subaru WRX, Nissan 200SX, Nissan Skyline and Universal Fit.   Check out and hear the Whistling Trumpet for the Stealth FX   Colours available: red, blue, silver or black.