I think the HHO is a red herring. A normal alternator will never produce more that about 1.5 HP. It take about 2.5 time the amount of energy to crack water as you get when you burn hydrogen (thats why water is so good at putting out fires) So the best you can hope for i about .5 HP. out of the system. I figure that when the vacuum on the engine increases you end up with a very fancy water injection system. And water injection can increase horse power and milage.
Jay