Small Block 265-400, Retro-Fit Roller Lifter for Early Model Blocks Originally Equipped with Flat Tappet Cam, Tall Body Fits Both Standard Blocks and Tall Lifter Bore Aftermarket Blocks, Short Travel, Race TypeeDesigned to perform at higher engine speedsWhen equipped with hydraulic lifters, high RPM is limited by improper position of lifter's internal piston as lifter "pumps up"Improper location results in open valves that lead to lost power and possibly engine failureMinimize internal piston movement to allow higher engine RPM