I had my pistons and chambers coated at swain tech.
www.swaintech.com
They are higher rates but back a few years when i did it the prices were a little lower. reallly good work. Gold coat on the crowns, moly coat on the side and coated chambers and exhaust ports. exhaust valves are coated up the stem a little too.
i figured if the piston top coated keeps heat out of the engine and piston the coated chambers and exhaust ports keep heat out of the engine and out the turbo housing.
i ported the head and exhaust ports myself before getting them coated. The gold coat has to be installed and the engine started quickly because the coating will absorb moisture and start to turn a greenish color.
i do believe coatings will help keep heat out of the engine and thru the turbo. oh yea my exhaust housing and DP is ceramic coated. i would like to get my next dp coated by swaintech with the white lightning coating which is supposed to be cool to the touch quickly after you cut the engine off.