can there be more miles per gallon if we can make more HHO gas?

a normal car have one generator, which can make power output about 600-1000W. and not all of this power can be used for hho, because there are other needs for electricity, such as lamps, batt charging a.o.
- at the end we can take only 200-300W. but if using two generators - than summary power for HHO can be about <1000W in ideal conditions. this makes about 3 liters hho per minute, compared to ~1 liter per minute with one generator.

car audio enthusiasts sometimes use two generators, and also couple of batteries, to supply special unnormally loud audio systems for loudness-drag championships.