Do not take this the wrong way, but I'm getting tired of saying the same things over and over again (becasue I'm mad at myself that I don't have time to follow up with this project and contribute some useful, actual data!!)
Every cell is different and unique. You might very well be able to build a cell that's small yet produces fuel to make a noticeable difference. But here's some food for thought:
From what I've read and experimented with myself, it takes a rather large cell to produce enough fuel to even make a difference on a small 5 hp B&S engine. And you can't even run that same 5 hp B&S on straight HHO at idle. Even that small motor consumes way too much volume. Only way to do it would be to take a large, thick skinned 'balloon' and use it to store up HHO gas from your generator, then you could actually start and run that 5hp B&S for several seconds. Then you need time to generate enough HHO to do that again. So your LPG tank, even though turn 'low' still has a pretty good flow coming out of it, much more than a small cell like you described is capable of producing.
You could probably run a 5hp B&S at idle with a unit the size of several 5 gallon buckets, with an optimum design, but I'm not sure. That's one project I wanted to complete, to run a small elect. generator on HHO, but for it to even idle we're talking about a large cell...
Now think of what you want to do with a motor HOW many times larger?
This guy's cylinder of water was about as big as a roll of paper towels and he claimed 10 hp gain. How large would we need for a 35 hp gain?
10hp on a very small ci motor is way different than 35 hp on a BIG ci motor, as far as volume of fuel required to produce said gains.
It plumb takes A LOT of HHO to make a difference.
But with some careful engineering and LOTS and LOTS of experimenting, I bet you could build a HHO generator that would fill a normal bed tool box, that would produce enough gas to make a 1 or 2 mpg
difference at best (which would be cool in my book!!). Someday when I get caught up and have some extra time, I'll get back on the project. For now I just keep tripping over the cell I have in my shop, reminding me what I'm missing...