the reason you NEED GSR (or type r) belt and pump are because the belt is actually longer than the b16 belt, and the pump is a different shape (larger than the b16.) the belt is longer to fit on the taller deck height of the b18 motors. any b18 belt will work, and any b16 belt will be too short. the water pump is a completely different shape, the b16 one is much smaller in diameter (just the case, the impeller is the same) than any of the b18's. and like noted, the type r has 22teeth, which will slow down the flow of water and prevent high rpm cavitation.