As I understand it, in American planes, water injection did and allowed the following: It cooled the cylinders, which let the crew chiefs up the turbo pressure, so the engine wouldnt blow up at full rpm. Higher turbo pressure meant more air/fuel burning and more horsepower. Souping up an engine without water injection would cause it to blow sooner. Pilots used it judiciously. It also allowed for a denser oxygen charge as cooler mixtures contain more oxygen.
