your gonna need to scuff it up first off... then look at using a high temp engine enamel or go the extra mile with the ceramic stuff. They sell it in rattle can form at most auto parts stores. Shit takes a long time to cure between coats, but it'll stay on there.
EDIT: found it -
http://www.duplicolor.com/products/engine.html
EDIT: found it -
http://www.duplicolor.com/products/engine.html