So, how do you vary HHO output? And how much power does HHO use?

[Lorena_Palin]

So, question:

Per litre (or whatever unit of volume you want to use) of HHO produced, how much power is needed?

Also, in a system with a separate battery setup to power the HHO, can you increase the amount produced on the fly by increasing either the voltage or the amperage? Ideally I'd like the ratio of HHO to normal fuel/air to remain constant no matter what the throttle is at.