First off you would have to use pure deionized water or else you would get buildup on the pistons from when the water boils off and the everything else stays behind (like boiling salt water).
second you would need a water tank to keep up with.
Third you would probably run the exhaust through your water tank after the catalytic converter to pre-heat the water before it is injected into the chamber, and if you kept the water at higher pressures then it wouldn't boil until the pressure lowers.
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