When ever I use a MagnaFlow, I only use one outlet of the pump to feed the engine, and the other outlet to go overboard. By putting a gate valve on the overboard side only, you can control how much water you waste, (waste gate).This way, there is very little pressure on the block and the water pump. This is especially handy when running aluminum heads where you need them to be at least 180 degrees and ideally 200.