Re: [Fot] Fot Digest, Vol 66, Issue 9-Stahl header

[Duncan Charlton <duncan.charlton54@gmail.com>]

Mike,

Several sources claim that keeping heat in the headers causes the gases to
exit the system faster due to decreased density.  I haven't pursued the
science behind this.  One header wrap vendor says hotter exhaust gases are
like hotter liquids that lose their viscosity as they heat up, creating less
resistance to flow.  I'm not sure I buy that explanation.  We would probably
all accept the claim that the velocity of gas flow is important on the intake
side of an engine, although we would also agree that higher density
(cooler=denser) of the incoming charge is good too.

Whatever the true cause, Cool Concepts Performance Coatings goes so far as to
cite dyno tests (but I didn't spot any graphs or explanation of test
conditions there).  From their website: "Dyno tests have revealed power gains
of 8-10 hp in a 550 hp engine. This is mainly due to the heat barriers
trapping heat inside the header pipes and increasing exhaust velocity. It was
also acknowledged that more gains could be had when installed in an engine
bay, where hot air robs power."  Presumably the latter refers to the heat from
the headers causing the intake air to be hotter and therefore less dense.

I'm using coated headers on both my race car and a street car.

Duncan
(Texas)
1952 Morgan Plus 4 red #6


On May 4, 2012, at 7:38 AM, George Harmuth wrote:
>
> Follow up question, ceramic coating or not? My thinking is not to coat, let
> the gas cool quickly and contract, reducing the volume and back pressure.
> Less pressure == better flow?
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