Alloy Atmospheric Ram Dump Valve Fitment Guide Evo 1 Evo 2 Evo 3 Evo 4 Evo 5 Evo 6 Made from billet aluminium, this atmospheric diverter valve dumps the charge-air to atmosphere creating the "Whoosh" sound most commonly associated with rally cars. 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.