i am building a hydrogen fuel cell to put in my car will it hurt my car?
You're confused. A fuel cell consumes hydrogen, burns it, and generates electricty. What you are building is an electrolysis unit that generates a tiny amount of hydrogen. Good question about getting the engine hot. I never ran an engine on hydrogen, so I'm not going to pretend to give you an answer. I'd say that's just part of the experiment. It can't possibly improve your gas mileage, though. Sorry. Your car is carbureted, so even if you had a source of hydrogen that made thermodynamic sense, your car isn't able to make any adjustements for that.
You have the mechanical skills and chemical expertise to do that? I'm impressed. All the car manufacturers are spending billions of dollars on the same thing, if you can do it in your garage, you should become rich and famous. I would guess you would need to install it in the rear seat/trunk area and put a Lexan firewall behind the front seats - depending how big the unit is. You will also need to install a separate a/c unit in the fuel cell area to purge it of any excess gases. Good luck - post photos on line.
actually they produce less power than gas. it will leak out of every joint because it is so thin. The heat generated depends on how you have your engine setup with timing, etc. We had a ford unit here where I work. Lots of stuff to add to make it work.
If you can build a hydrogen fuel cell by yourself, you clearly are more then capable of adding the required safety measures.