I can't see what numbnuts is saying, though I imagine he his still trying to hide his numerous and egregious errors and salve his ego behind a bet about rusty, or maybe we are back to garbage cans, or proving the earth is flat, but basically what rusty is saying is best understood with a video. Though in this video, the area under the solid green line to the left of TDCC isn't very much but increases with more rpm and more vaccum (whenever ignition is advanced), certainly not enough to get you from 12 to 17 mpg. It describes the effects of rpm and MAP basically. Supposedly we get less area under the pre-tdcc pressure curve with HHO while maintaining pressure peak at ~10 degrees ATDC (via faster combustion of the whole charge making the curve narrower).
If the energy to make the hho is less than 2x the area under the curve left of tdc, you "win", so to speak, approximately of course.
edit: note that "energy" under the curve is the integral of pressure and swept displacement, not accounting for heat loss.