These are the same Springs and Retainers we install in all of our Hydraulic Roller heads. Designed to work with all our Hydraulic Roller cams from 1.1 through 2.9X and yeild 150# closed seat pressure at 1.650" Installed height. Designed to be used with Boport or other .400 or .470" tip length single keeper groove valves.  No spring pocket machining or valve guide machining required with correct valves and stock heads. Select valve tip length so we can supply the correct valve locks for proper installed height. Available in X series that are Polished and micro-finished to relieve stress for increased durability.