Well....
Those who say it's theoretically impossible are wrong, they don't even know what theory they should be using most of the time, however, those who say it's easy don't know much about the theory either and many of them "got lucky".
There are a ton of self deluders into this as well, when they fit the kit, fill the tank, drive 100 miles and can only get a cupful of gas back in, what happened? .... the gas in the tank expanded.
The reality is that there is a relatively narrow range of parameters for this to work, and it's a little different for every engine... and that's before you start fighting the computer controls.
I know a smart guy, builds engines for economy and power, lost his shirt in trying to commercialise this and related technologies. The potential is there, but individual engine setups are just different enough that you can't write a recipe for success that works on all of them.
All this is really to say, that this is best classed as "experimental" and there's probably no pre-existing magic recipe for your particular vehicle.
Other factors...This isn't going to cure below par engine performance or bad driving habits, if you can't get "stock" economy, there's something wrong.
I have been researching this seriously for 5 years or so, but I don't have a system on my vehicle yet, it's taken me that long to sort out the BS and find the right science to work with...then I've been "test benching" various setups in my head and finding problems, I'm somewhere near something acceptable that I would try running on a car now, but it still needs lab work to settle a few parameters.
A brief summary of why it can work, and what one needs to research into to make it work.
i) engine efficiency is not the same at all RPM and VARIES WITH LOAD
ii) engine efficiency is affected by the thermodynamic properties of ALL of it's inputs. (And we're not talking pure air and gas any more)
iii) Most of the energy in gasoline is wasted, sometimes as much as 85%, according to where in the operating range the motor is, this can be scavenged internally or externally to increase the total efficiency of the system.
iv) electrolysis efficiency is determined by it's TOTAL energy input, at room temp 70% comes from ambient temperatures.
v) it's really important to remember that you're not going to get free energy, it's coming from somewhere, you're just redirecting it to be more useful.
regards,
Flashman.