The intake manifold should stay painted if some type of "high heat" enamel is used on it. Exhausts- - - -about the only thing I've seen that stays put well is "stove polish", the black greasy stuff that old-time wood stoves got treated with periodically to retard rusting. It's basically carbon black powder suspended in a beeswax/grease carrier that burns away, leaving the black pigment behind.
Jerry
One of the old street rodder tricks that ran chrome headers was to spray the inside of the tubes with white lithium grease before installation. It is supposed to burn on and create some sort of coating that prevents blueing. My personal experience in my very young days was to try it on a new set of cheap headers. The factory paint lasted many years which normal experience was it lasted very few minutes. I don't know if this applies well to this conversation but if exhaust is off, it can't hurt and may help prolong any coating put on the exhaust manifold.
