Fit 5.9L 12 Valve motors. Kit includes heavy duty double valve springs with dampeners, titanium retainers, and hardened chromoly locks. For use with roller cams only. Retainers CNC machined in house. Requires machining of cylinder head for larger diameter springs. Requires removal of valve seals. Proven on Darren Morrison's 7 second 1/4 mile Pro Mod S-10 among others.