I've been wondering about this system for years. Basic physics suggests that it could well make a difference. If you mix water with your air/fuel mixture the water should absorb some of the heat from the air/fuel, giving you a denser mixture, and, consequently, more power. The cooler mixture should also reduce the effects of high compression ratios or low octane fuel.
Next, when the air fuel mixture ignites in the cylinder the water will vaporize, increasing in volume, which should increase cylinder pressure, giving more power. The vaporized water, as steam, should have some cleaning effect from the combustion chamber on out.
On the other hand, if this system actually did make a noticeable difference, why don't we see them in use now?
Maybe my knowledge of physics is faulty.
