ive seen a system that a guy put in his 4.3 V6 s-10 that used a secondary 100 amp alternator to run current through some sealed containers of water in the bed, with a collector tube at the top that went to the intake. the thing (he built it himself) seperated the hydrogen and oxygen from the water and he saw a 15 mpg increase, no word on whether or not its still running though lol