Pro Magnum Hydraulic Flat Tappet Lifters. Specifically designed to perform at higher engine speeds. Proper position of internal piston at higher RPM prevents lifters from harmful "pumping up". Unique design yields significant power increase over standard hydraulic lifters. Adjustable valve train required. Pre-load .002"-.004" with engine warm. Applications: Buick V8 350-455, Specifications .842" Diameter - 94g Weight - 2.01" Seat Height.