My older brother was big into HHO over a decade ago. My father asked me about it. That was the very point I made. I didn't know if it reached break even with improved combustion or not but acknowledged it was theoretically possible. For me it was nice to finally see an answer. Even if one has a more efficient HHO generator and alternator, and you exceed the required work for the HHO, the marginal improvement simply isn't going to be worth it.