Roger

Frequently we would like to make the tubes thin, but one has the problem
that the material thinning on the outer radii is too high. To get a robust
design, one wants the tubes to be as flexible as possible, but the minimum
wall thickness is dictated by what we can bend successfully. The stiffer
the tubes are, the higher are the loads that are created by thermal
expansion. The thicker the wall, the bigger the temperature gradient in the
steel itself and the higher the thermal inertia (resulting in uneven
heating and cooling).

I can assure you that the only reason why the manifolds in the EU are
fabricated is for weight reduction and survival at gas temperatures over 950
degrees C. In racing circles, the highest cost is for labor and generally
the highest quality materials are used (Inconel) and they frequently can be
very durable indeed. The cost calculation is very different when losing a
race could result in losses of 100 000's of Dollars. The turnaround time
for replacements is also a pretty big issue since the components are
generally hand made.

If you want to see an example of a air gap insulated manifold, you should
take a look under the hood of a current E class Benz.

Keith
"Roger Halstead" schrieb im Newsbeitrag
news
There are a lot of , for lack of a better term, "old wives tales" that
develop in these trades.

They are talking headers. All performance headers I've see on race
cars were developed for high performance and made as light as
possible. Not a combination that would indicate a long life product.

Show cars OTOH may have massive, chrome, or ceramic coated headers.
Sure they are tuned for performance, or most are, but they weren't
built with weight savings in mind.

Back when I was playing around with street rods...a very long time
ago... we paid a lot of money for the big name headers which lasted
about as long as the packing in a steel pack muffler which was a
fraction of a glass pack.

When I got to that temperature amplification part the site lost a lot
of credibility.

As to the wrap, or dual tube air gap insulated I would think a
manifold and exhaust ceramic coated within an air gap insulated tube,
or the ceramic coated tube *inside* the wrap would be the way to go.

I can see where a dual tube, air gap insulated exhaust could scavenge
the air through the gap cooling the tube (much like an augmenter) and
pretty much keeping the engine compartment cool...or as cool as you
can expect with an air cooled engine.