Thermal coatings

[Bruce]

The really well done ones do inside and outside.
The home brew guys generally don't take the time to tie a string to a rag
(soaked in whatever thermal barrier stuff they're using) and drag it thur
the piping.  Couple hundredths (in I.D.) isn't going to matter that much
anyway (street car disclaimer).
>From the limited few I've seen, I'd bet there is less carbon build up on the
barrier coated ones anyway.  So long term the they might be better then
first imagined.
Bruce


> The ceramic coatings I've seen on exhaust headers go on the OUTSIDE of the
> header pipe.  The inner diameter is not reduced.  If there is less heat
> transfer away from the exhuast gases, the gas is hotter and therefore
lower
> density.  Lower density does yield a lower Reynold's number with all other
> things being equal.  Speed of sound within the exhaust gas is also higher,
> slightly raising the "tuned" RPM if it is a tuned manifold.  Coated
headers
> don't heat underhood air as much, allowing more of the heat to be passed
> through the exhaust system further downstream.


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