Your chemistry is absolutely wrong. To begin with, any scientist worth his salt doesn't use the BTU; calories or joules are preferred. Second, delta G, or the change in Gibb's free energy, for the electrolysis of water under ideal circumstances is roughly 237.1kJ/mol. The inverse reaction is -237.1kJ/mol.

Again, those are under absolutely ideal conditions. In reality, an efficiency of 70% is really good, and that's only considering the net loss of electrical energy to pure hydrogen's chemical. More realistic numbers are far lower, especially with less precise (i.e. homebrew) rigs.

The argument you presented above suggests a "free energy" situation. If you actually stumbled upon a chemical process that releases more energy in one direction than it absorbs in another, you would have solved our planet's energy crisis.

I'm sure you don't have any reasons to tell stories or make things up, but I do think you're a little misguided. After all, what do we have to gain from convincing you one way or another? The science behind "hydrogen fuel enhancement" just isn't sound.

Additionally, the MPG "gains" you noticed aren't great enough to be statistically valid. Remember, correlation does not imply causality. There could be a variety of lurking factors affecting your MPG; the most likely being your driving habits. I don't know about you, but if I had a bucket of water sloshing around in my trunk and tubes full of flammable hydrogen running through my car I would probably be persuaded to drive more carefully.