HardDrive Polished BIllet High Volume Oil Pump 301493Harddrive oil pumps are made from cast aluminum that is CNC machined to close tolerances and then polished to a high gloss finish. Great value for small dollars! 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 bottom and top end oil supply which increases oil pressure to the hydraulic lifters