I don't know about a non-turbo, but a spraypainted turbo exhaust mani shield will discolor the paint after about a month. The paint pretty much just turns into ash.

I used 1600*F gloss black ceramic paint, baked in the oven at 600*F for 1 hour.



The grey is 1200*F "engine" paint and is pretty resistant to chipping and oil, but can't go on anything exhaust related.