Welcome to the site!
you will find that your hydrogen out the water "mod" has been tried many a time. I have yet to see hard ABA data that shows it helping. I keep an open mind but I need to see the data to believe it.
Get me some reliable data though and I can add it to our wiki of car mods (in the pending more data to be proven or in the hoax section depending on the data):
Car MPG Efficiency Modifications Main - EcoModder