HHO generators need to be Sealed, and made into the shape of an upward turned horse shoe to be able to create H and O at the same time.

Glass jugs can be used as long as they have a flow tube between them at the bottom to allow the water to be the same level between the 2 jugs. It doesn't have to be made that way, but it seems to work best.

When High Current at Low voltage is applied, H is created in one jug, as O is created in the other.

And if they are sealed, the Gas pressure can be vented and separately channeled into a carburetor to increase fuel mileage by almost 75%. But gas or some other fuel is needed to keep it going.

It would take a great amount of power to turn enough water into H and O to fuel a small car at any normal speeds. A car would have to have quite a powerful battery system, and an alternator large enough to charge it.

I'm not sure if a Higher voltage will make any difference. If it would, then by Rectifying 110 AC into DC, it could do what you need it to do.

If this is the case, then a small AC power generator could be used to power the HHO generator and the car can run completely off H and O.