I don't want to burst your bubble, but if you can get the compressor in a
car, it's probably not big enough to do spray painting.

Good spray guns need about 15 SCFM.

There's a bunch of newer conversion guns on the market that use less air.
They'd more accurately be described as MVLP (medium velocity). Most of these
work at 5-10 CFM and they're fine for most woodworking projects. A typical
25 gallon unit is usually sufficient to run these guns.