Last summer, I overheard someone who had experience
with the engines of cars, of several decades duration.
I heard him mention that he had added a structure
to the engine of his pick up truck
that ran an electric charge thru some water, separating
hydrogen from oxygen, and that the hydrogen yielded 40% better gas milage
when combined with his normal use of gasoline consumption.
I have no expertise in such matters; I cannot judge this.