A fellow racer showed me his header off his old 1.6L Miata engine he swapped out to 1.8L.

He told me it was ceramic coated aluminum and I did not believe him; until he took out his pocket knife and carved off a section from the inside where he had ground through the ceramic when port matching the flange. It was also suspiciously light.

So yes, a thin coating of ceramic really does work as a thermal barrier to exhaust and combustion temperatures whether it is on a piston, combustion chamber facing or exhaust pipe.

If ceramic thermal barrier coatings (commonly called TBC) didn't work they would not bother plasma spraying all combustion surfaces of turbine engines.

Here is a link to a WIKI article on TBC
http://en.wikipedia.org/wiki/Thermal_barrier_coating

I know some top rotary drag racers using alluminum.