HardDrive Billet Oil Pumps are made from cast aluminum that is CNC machined to close tolerances and then polished to a high gloss finish. These pumps are a great economical choice! Surplus oil is routed back to the main passage rather than the return to avoid unnecessary filtering and offer the opportunity to upgrade earlier engines to the 81-up oiling system. This oiling system splits the bottom and top end oil supply which increases oil pressure to the hydraulic lifters and top end.