what is this part called ? Exhaust related
 

I don't have a picture but on race cars where the exhaust exits sheet metal on the body there is a trim ring or half ring that I guess acts as a heat protector for the painted body. What are those trim rings called ? I'm trying to search for them for a project I'm working on.

Here's what you need:
Flame Header Flange (Trim to Fit)


Flanges

Try "thru body exhaust" and/or "side exhaust plate" in Google...

You can also search marine applications as any 'through hull' exhaust needs a trim surround plate. Several companies making very nice ones........