can anyone tell me what the difference is between nitro fuel for cars and for planes.
would car fuel work in a plane engine, without damaging it?

A lot of car fuels have lower oil content. Some car fuel mfg actually advise that the fuel NOT be used in planes. Planes tend to run at more constant high RPM whereas car RPM varies a lot.

i have already used the little bit of car fuel i had left in an airplane engine (old engine i didn't care about) it might have something to do with the % of lubricant, but i may be wrong

Most car fuels have between 8-12% oil content and not many come less than 20% nitro. this means more heat.

On another note my buggy engines get either repinched or rebuilt every 2 gallons to keep them in
top running condition. Some of the veteran pilots on this site will tell you about their plane engines with
10 gallons through them and they still run great. Guess it's the fuel

As others have said, car fuels simply don't have enough oil in them for plane engines. On the reverse side of things, plane fuels work perfectly well in car engines. I have plane engines that I consider to be barely run in after 10 hours and I expect them to last for hundreds of hours but I don't skimp on how much oil I mix in when I make my fuel. Put it this way, the engine runs on the methanol and nitro but it's the oil that keeps it running .