These are a set of very high quality high pressure springs for the Predator 670 engines. This spring kit includes 4 springs and 4 CNC machined billet 7000 series alum retainers. The retainers fit the stock valves and keeper much better than the OEM retainers. Springs are to be used with aftermarket hard face welded cams only. Works with stock length valves and cams up to .250 lift.