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>Porsche has used ceramic coating in their turbo cars for years. NOT, mind
>you, in or on the Exhaust Manifold. Given that they saw the importance of
>ceramic coating in production turbo cars, and chose exactly not to use it
>the EM, one has to wonder, "why not"?
Yes, but I believe Porsches' intent was not just performance. Coating the
exhaust ports as they did on the 944t can significantly reduce head
temperatures and help prevent overheating. This was probably more of a
reliability issue then a performance one. If cost was no object then
Porsche probably would have coated the EM. Coating the exhaust ports,
valves, combustion chambers, piston tops should be addressed first as you
will see more gains per $ here. However, there is absolutely no sound
reason _not_ to coat an EM except cost. But even this can be justified.
Coating the manifold will extend it's life. Furthermore, it will lower
underhood temps. How many components fail due to extreme heat? Motor
mounts, wires get brittle and crack, hoses, etc. There are clearly numerous
advantages to coating the EM. Furthermore, the performance advantages of a
coated EM are not in the absolute HP numbers but in the improved
responsiveness of the engine (turbo). This is clear if you understand the
theory and I do. It has also been stated by Eric. I don't have that turbo
book you always quote but I have taken numerous courses in thermodynamics,
materials, flow, etc. Maybe your opinion would be different if Eric's was.