Red Shift Dual Piston Cam Chain Tensioners + Axtell Oil Bypass Valve Fits 2007-Up Big Twin engines, 2006 FXD engines, and all 1999-2006 Twin Cam engines converted to hydraulic tensioner systems. Dual Piston Design Eliminates Chain Instability & Tensioner Shoe "Rocking" Facilitates Accurate Cam Timing Events for Both Cylinders & Tolerates Common Crankshaft Run-Out (Unlike Gear-Drive Cams) Improves Throttle Response, Acceleration and Across-The-Board Power With the added Axtell Bypass Valve you can expect higher, more stable oil pressure at all engine rpms, longer oil life due to reduced oil shear, lower oil and engine temperature, improved valve train control and reduced noise.