1681CI 1963-1977 Small Block Ford cast iron 5-9/16" water pumpSmall block Ford running hot? Flowkooler designed a high flow water pump with a CNC machined billet impeller, an increased vane count and a reduced casting to impeller vane clearance. It achieves greater flow rates, higher head pressure and a more efficient flow. The impeller color is due to Type II Class II military grade surface coating which protects against corrosive fluids. FlowKooler introduced the first hi flow pumps and continues to improve