Rolling Thunderz has expert knowledge of Viper Cylinder head technology and extensive experience for applying the right cylinder head modifications to the many different performance requirements for Viper engines. This is the reason that Rolling Thunderz Performance Enhanced Viper Cylinder heads power some of the best performing Vipers. This Viper SRT 10 - Phase 4 Cylinder Head with 2.055 Intake Valve Flows 300 CFM @ .550 Inch Intake Valve Lift.