Zetetic -
I have a post for this :
Hydrogen Booster Installed ...
http://www.gassavers.org/showthread.php?t=2668
Like Spence says, the 02 sensor will cancel out the gains. The dude that provided me the solution instructs me to replace the exhaust 02 sensor with a potentiometer in order to make it work. Since I want to be emissions compliant, I don't want to do this. However, I am going to put a bias on the 02 sensor with an EFIE gizmo, which was another option he said would work (but less efficiently).
I have seen no gain, but like I said, I never installed the whole system as instructed.
Hydrogen generators are ideal for diesel engines because of their lean-burn capability. There are after-market hydrogen generators for truckers that give you a two for one, improved emissions and improved FE.
CarloSW2