I have finally worked out a cell design that will allow the flow of water through the cell. The water and gas exit the cell at the top and the water is picked back up for return to the holding tank while the gas goes up into the line going to the engine. This will significantly reduce the amount of HHO gas waiting to be burned. With a little flashback control and the amount of gas stored in the lines drastically reduced will only provide a small pop if ignited.

BEHOLD! more of my MSPAINT skills! lol

Here is a diagram of the cell prototype. I think 3 of these units will run the engine just fine with gas to spare. Throttle can be controlled by the PWM.