Cold water fog/mist into intake cools intake charge/increases density ergo turbo boost pressure = higher compression... Combustion, with or without HHO, flashes water to superheated steam = higher compression. Steam wishes to occupy about 1600 times the physical space (at atmospheric pressure) that the amount of water that made the aforementioned steam previously occupied. Except it's not at atmospheric pressure is it? NOooo.. It's crammed into the top of a cylinder with a bunch of burning hydrocarbon fuel and donating it's expansive energies to the general push to get out = more bang for the buck. G'nite...