We have upgraded our exhaust valve technology from a membrane bellow style actuator to a piston style actuator. A much simpler design that uses less components and eliminates bellow failure in big bore and turbocharged applications. Our piston mechanism stays lubricated by the engine's 2 stroke oil system and is actuated by the exhaust pressure from the cylinder. Same design works well with naturally aspirated engines as well. We developed this valve design in the fall of 2010 and tested them on turbocharged and naturally aspirated engines throughout the season with amazing results. You will love the throttle response gained. Say goodbye to failed servomotors and stretched cables. There is no need to play with cables or reprogram your CDI to change the opening RPM of the valve. You can adjust the opening RPM by changing different thrust springs. Assemblies are shipped pre-calibrated ready to bolt-on and ride. We do stock different spring combinations for finer tuning: Kit # 78SPNG sold separately Applications only for models 2007 through 2011. F8 & M8 F8 HO & M8 HO F1000 & M1000 F1200 & M1200 BIG BORES The valve housing is made of billet treated aluminum and valve blades made of billet high carbon heat-treated steel. We also include a plug in chip to the ecu harness that allows you to remove the servomotor without defaulting the ignition timing. Complete bolt on and ride assembly and includes tools. Overall dimensions are 2 7/16” high x 1 3/4” diameter measured from cylinder mounting surface.