Powdercoating takes 350-400* for 10-15 minutes. Never more. Ceramic coating takes 500*. That will not affect your casting in the least.
Where did you get your information?
The company that coated my pipe with ceramic said the pipe will not get over 250 degrees at any time during the coating process.
I also have my manifold coated.
Its a thermal spray then it gets put in a vibrator to be polished out.
Im pretty sure this is the temp they told me, Im going to shoot the guy a email and confirm.
Ok just called the guy.
He said they normally take a part up to 500*'s depending on what the part is made out of. He took my pipe up to 300* and just baked it for a lil longer time than if it was at 500*.