Ok, I have heard of this mod for a while now. I don't know all the details, but basically you make a concoction of chemicals that gives off hydrogen gas and is sucked up into the intake manifold. The creator of this video is claiming a 38% improvement in a escort and a 43% improvement in his Saturn.
[YOUTUBE]http://www.youtube.com/v/YFGhZNxdyDY&rel=1[/YOUTUBE]
You can see the rest of his videos here:
http://www.youtube.com/sm0ky40