If you Google HHO you will find all kind of information on it. Forget about the ones who are selling HHO units and concentrate on the articles.
I haven't started building one yet, but I am convinced it can greatly increase gas mileage if you put in the proper unit. There are some things you need to do to get the most out of an HHO unit.
The type of electrodes you use can make a difference in the output of HHO gas. There seems to be a general consensus that spiral electrodes work better than plates.
Modulating the power increases output while using less energy, and the modulator can be bought or you can build one.
HHO gas introduces more oxygen into the exhaust causing the computer to richen the gas mixture. For maximum efficiency you need to fool the computer and you can get a unit that does just that.
For safety make sure you use a bubbler, that prevents a spark from reaching the HHO unit and causing an explosion. They are a very simple device and there is no reason not to install one.
