Alloy Atmospheric Ram Dump Valve available to fit the Impreza 2001 onwards models including the 2009 GR STi Made from billet aluminium, this atmospheric diverter valve dumps the charge-air to atmosphere creating the "Whoosh" sound most commonly associated with rally cars when the throttle is lifted. This increases both quicker throttle response and higher clamping load to maintain boost pressure more reliably. Dual-Piston Atmospheric Valves and Valve Fitting Kits All Forge Motorsport Dual-Piston Atmospheric Valves have been designed and built with the intent of venting 100% of the residual charge air remaining in your forced induction system to the atmosphere at throttle lift. While we have incorporated many elements into the design of the Dual-Piston valves to aid in their compatibility with mass air-flow sensor equipped vehicles, we cannot always guarantee that each individual’s application will be compatible with a valve that vents the charge air into the atmosphere. Forge Motorsport nor any of it’s Authorised Distributors can assume any responsibility for any adverse effects resulting from the installation of this valve onto a vehicle whose engine-management-system, whether factory or aftermarket, is not capable of compensating for the loss of metered air through a vent-to-atmosphere valve such as this.