OK, so here they are HPC coated, very pleased with the result too.
I have made 2 experimental exhaust valves which divert exhaust from the underbody pipes to the sidepipes and can be adjusted to tune the sound. I had a spigot and blanking plate put on when the underbody pipes were fabricated.
They work well so far but dont know if the high temperatures will cause them to sieze in time. At present they are adjusted by hand but might put a cable or motor drive in if they prove to be durable.
