Quoting Beaner:
You could coat the manifold with anything you want and I bet you'd never notice a difference. You would be more interested in a phenolic spacer though. It keeps the manifold cool to touch after driving around. I have one I plan to install soon only in the interest of getting an extra inch in length for the runners. The gains from the cooler manifold are about zero according to my searching around on Google.
cooler manifold at first.
I had a Phenolic Spacer on my stealth, with an infrared Thermometer it read 45* cooler when at idle vs with out.after 10 minutes, hood closed.
but after driving, the manifold temps were exactly the same +-5degrees.
Spacers work well on NA engines, but youre forcing hot air in there, so the temp is going to come up regardless /ubbthreads/images/graemlins/smile.gif