heat wrap/shield (Peter Schulz)
sidman at webloq.com
Wed Feb 1 20:14:43 EST 2006
In the sixties I restored a 1936 Bentley that had all the exhaust components
wrapped in asbestos and covered with shaped aluminum covers. The car had
80,000 miles on it and the exhaust system was in perfect condition. It was
made of standard steel, not SS. In later discussions with RR engineers, I
learned this practice was carried well into the early sixties.
It served three purposes. Heat concentration, noise isolation, and slow
cooling. The first two were obvious, but the third was a surprise. When you
turn off a hot engine, moisture is drawn into the exhaust system. If you
start it up and drive a short distance, the exhaust gases mix with the
residual moisture, creating an acid brew which then rusts through the bottom
of the mufflers and pipes. Which is why folks who have a short commute burn
up mufflers. A long drive burns out the residual and the problem is much
less. By wrapping the system, their logic was that much less moisture would
be drawn in because the cool down would take much longer, and the more rapid
heat up would more quickly burn off internal nasties.
For whatever reason this wrapping practice was discontinued in the
mid-sixties, and flat heat shields were hung under the frame to isolate
I have never tried this on another car.
Chairman & Chief Technology Architect
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