Ive found that it's not the paint (either rattle can or spray gunned) as much as the prep. I've been epoxy priming bare metal, both cast iron heads and block and sheetmetal valve covers etc prior to spraying on color for years. An inexpensive alternative is to use self-etch primer ina spray can. Any body supply store will have it. Don't go overboard.. just dust it on light to achive hiding then go over with your engine color. My oldest was done in '92... no peel or flaking.