Originally Posted by corsair23
assuming someone can tell me this won't cause my engine to melt down
If you assume that the amount of H2 produced is not really significant, then I don't think you'll do anything that the ECU and ignition advance won't be able to deal with. My guess is the main immediate concern would be not passing the tailpipe emissions tests anymore. While the catalytic converter prefers a slightly lean condition for the oxidation reactions, if you lean out too much the reductions won't be balanced. At a slightly rich condition, the NOx reduction is favored and if you are abnormally lean then you might not reduce enough NOx and that could fail your test. I'd have guessed on an 80 series with an O2 sensor after the cat that the ECU would run rich to keep the reactions balanced and so that would compensate out any MPG gains you might get from introducing hydrogen into the intake. A single O2 sensor system would just be shooting for 14.7~14.8 stoichiometry and so adding fuel into the intake might make the ECU dial back the fuel injectors, that seems logical I guess.
The unburned HC oxidation
Carbon Monoxide oxidation
Nitrogen reduction (this is the NOx)