Competition Cams 858-16 Pro Magnum Hydraulic Lifters for Small and Big Block Chevy .842 diameter; 99g weight; 1.93 seat height Specifically designed to perform at higher engine speeds with significant power increase over standard hydraulic lifters Proper position of internal piston at higher rpm prevents lifters form harmful inchpumping up inch Adjustable valve train required Pre-load lifters .002 inch-.004 inch with engine warm