1684 1966-1980 Chevy GM 366 427 water pumpBig blocks in big trucks need big cooling. We designed the 1684 pump for the 366 and 427 ci blocks. It has an impeller with an increased vane count and a reduced impeller vane clearance to take care of the problem. 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