Fitment: 1973-'91 Big Twins. Features & Benefits:Same width oil supply and return gears as the stock HD® aluminum pump. S&S pinion and oil pump drive shaft drive gears increase potential oil volume delivery by 25% over stock on 1972 and earlier engines. Machined with an oil pressure relief bleed off passageway & relieves pressure build up on top of the valve to maintain consistent oil pressure. Oil pressure regulation bypass routes excess oil directly to the supply side of the pump & reduces the amount of oil returned to the tank, less foaming and cavitation. The standard pump cover allows total flexibility for oil system configuration with a number of oil feed and return options.