COMP Cams 865-16 Pro Magnum Hydraulic Lifter for Buick 350-455 V8 and 183-252 V6, (Set of 16) 0.842 inches diameter; 94 gram weight; 2.01 inches 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 pumping up Adjustable valve train required Pre-load lifters 0.002 inches - 0.004 inches with engine warm