I'm not trying to say HHO doesn't work. I KNOW it does. But I believe the gains are from burning more of the gasoline or diesel that normally just passes out the exhaust.
My figures were solely to prove that HHO should not be classified as a fuel additive by those states (like CA) that regulate, and must approve, such additives.
1991 Plymouth Acclaim 3L V6.
1 dry cells with nineteen 6"x8" 316L ss plates, driven by constant current PWM set at 35 amps (13.3V at PWM). 28% KOH electrolyte. Total measured output 2.5 lpm. Mileage went from 18 to 26 mpg, all city driving (44% increase). EFIE set at .370 and I still need to play with ignition timing.