1687 1971-1977 Inline 6 cylinder 250/4.1L 4 1/4" tall water pumpIf you have the 1971 1977 Chevy truck with a 250 4. 1L you might be finding it runs a little hotter now. You might also find heat cycling is occurring with your riser set up. Either way, the 1687 can help the problem. We designed a impeller with an increased vane count and a reduced impeller vane clearance to take care of both problem. It achieves greater flow rates, higher head pressure and a more efficient flow and squeezes that air out of your