1975 SBC 5-13/16 with 3/4" shaft water pumpSmall block Chevy running hot? This is the 5 13 16" hub with the 3 4 shaft used on the 350 5. 7L. It has 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