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So you don't think it matters that my crank pulley is smaller than the 3groove crank pulley that was on the 340? Could this add any power, like a underdrive pulley?



You need to see if the pump is the bigger diameter, 8 blade, or the smaller diameter 6 blade to determine the speed it should run. The big diameter impeller should be at .95 ther crank rpm and the small diameter impeller should run at about 1.3 times the crank rpm. Be sure to measure the pulleys at the pitch diameter (not outside diameter) when you do your calculations. Pitch diameter will be about 2/3 of the way up the belt thickness.