These things do not work...think of it this way...You are saying you can get "something from nothing" perpetual machine [?] To get the hydrogen you will be using a wire run from your alternator. You then put an extra load on the alternator to produce this HHO. What drives the alternator? Will you not have to use more energy from the engine to keep the alt out put high enough to keep up with both the engine and the HHo system?

Best way to get better fuel mileage....drive differant.