I've heard two stories as to having
them coated. Tom says racers do it after running them to get them sort
of normalized. Others say 321 doesn't need it.
Kevin,
I had my 321 SS exhaust ceramic coated by
a company called Jet Hot. They have a ceramic coating that will stand
2000 degrees. The big advantage that I see to the coating is that, it
keeps the exhaust pipe from absorbing as much heat from the hot exhaust, and
also it radiates a whole lot less heat inside the cowling. It was also
pretty cheap to do. As I recall, about $50.
I've been very pleased with
it.
Here's a link to their website, if you are
interested.
Steve Brooks