How much of hho gas a minute do you require to run a vehicle?

If you are referring to water split into oxygen and hydrogen through electrolysis, the answer is alot; and far more than the onboard, engine driven electrical system can generate. If this were possible to run a car on solely "HHO" it would be the equivalent of a perpetual motion machine, and regardless of every conspiracy theory out there; every manufacturer would sell an "HHO" powered car.