Engine paint

POR15 makes an engine enamel that's supposed to be good, I'm spraying my nailhead with that this weekend hopefully. You can also brush it on. They also make POR20 high temp exhaust manifold paint, I'm using that as well. Neither of the POR products require primer but all 2K automotive paints do. I assume rattle can stuff does as well but I don't know, never use the stuff.

Regardless of what you use, getting the block Howard Hughes clean is the key. Paint doesn't stick to dirt or grease for long.