Spraying before charge cooling can cause the water to condense and turn to droplets instead of vaporizing and reaching the combustion chamber.
Recent study's by BMW show that the most efficiency, knock limit gain etc. is made by mixing water and fuel under high pressure and inject with direct injection. Next best option is port injection.
The usual aftermarket approach is to inject after charge cooling and cool the air charge before it enters the combustion chamber if there is a long enough routing like on turbos.
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