Zero fossil fuels has done some tests for the addition of HHO to gasoline for running internal combustion engines, i think understanding his research, the results of which he points out in this video, will help you save time and money while you are working on your project.
if you are trying to run hydrogen into your car engine to make an improvement on gas milage, you can do this, but it requires a lot of hydrogen, in the range of 15, 20, 30 liters per minute, to see an improvement, and anything less than that is useless.
these are not my conclusions, but his, as explained in his videos.
there is also a research paper from some university in Australia that did similar tests and got similar results, you can find that information from some of smack's videos on youtube