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

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.

Your would need minimum of 1 LPM, if over 3000 cc engine, you'll need 2 LPM, running at around 18 amps, you'll need neutral plates and a PWM, no need for an addtional battery

in order to do what you would want to do, the output would have to vary according to throttle position and level of RPMs. in order to change the output, you would have to vary the current going to the generator. in order to do this you would either have to increase the voltage or decrease the resistance. both of these are extremely difficult to do in order to keed the same A/F/HHO ratio like you desire. most set theirs up to give them the amount needed at cruising speed.

also, there hasn't been a single credible person on here that has shown results from an HHO setup. it doesn't mean that it is impossible but everyone is still waiting for the results that will tell the tale. there are many drawbacks to such a system.

I would think that if you did want to experiment with such a setup that you would want to start simple and slowly increase in your complexity.

my personal opinion is that you can't get the energy equation to work out with a net gain and if you can, you will never see the famed DOUBLED mileage that so many web sites claim.

if you do decide to experiment though, good luck to you.

Mechanical means to regulate production could be employed, such as arranging that the plates are raised from and lowered into the electrolyte with change in throttle position. Production is exposed plate area dependent. This would allow some tracking of consumption with production, but A/F demand is not really quite linear with motor speed and load, so extensive development with plate shape would have to be done to match the motor... like maybe hourglass shaped plates, with the thinnest point emerging/submerging at torque peak.

HHO problems
 

Do not forget that since you are drawing more current to power the HHO system than your alternator can produce, you must keep the battery charged with an external charger when not in use. Also, HHO systems put such a drain on your alternator that I highly suggest keeping an eye on your engine belt since it will start to show wear faster than normal. You see the same problem develop in marine inboard/outboard engines when boat owners neglect to charge their batteries. The belts wear out quickly because the alternators on these engines works much harder to overcome the dead marine batteries.