In order for this whole thing to work you need to use the following equations: you must have the chemical formula H
20 + energy → HHO to create the HHO gas from water. When the gas is burned, you have the formula HHO → H
20 + energy. This appears to not need any extra oxygen (as a combustion reaction would), since all this seems to do is rearrange the shape of H
20 to HHO, while storing energy in this new configuration.
This isn't electrolysis, as the H
20 is never split into hydrogen + oxygen. It's just rearranged into a less stable form with a lot of pent-up chemical energy. (At least that is what I understand from the information provided.)
When they refer to powering cars off HHO, I don't think they mean like the way hydrogen is used in fuel cells. Rather, I think all they do is take the HHO gas and feed that directly into the internal combusison engine in a regular car. The only modifications they need to your car is a new carburetor / fuel-injector to one which can handle the HHO gas instead of (or in addition to) liquid gasoline.