My stock cast iron manifold is around 5/16 " thick.  Paul Conner

----- Original Message -----
From: "Bill Dube" <bdube@al.noaa.gov>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, December 03, 2004 9:47 AM
Subject: [FlyRotary] Re: New Muffler Design


>
> >  I have the smaller 1988 cast iron manifold,
> >and including pipe, my total exhaust weight is 12 pounds.  What appeals
to
> >me most is that it is compact, simple, and I don't have to worry about
thin
> >walled pipes glowing red inside my cowling, as the cast iron manifold
> >absorbs a lot of heat that would otherwise turn exhaust pipes red hot.
>
>          The noise reduction with thick headers is real. Thin headers on
> cars make a noticeable increase in the noise level. They make a lot of
> high-pitched "ping-hiss" sort of noise. (At the instant you first
> disconnect an air tool, it makes this sort of sound.) It is like you can
> hear the valves opening through the thin-wall header pipes. The pipe
itself
> also rings with each exhaust pulse.
>
>          A thick-walled pipe only delays the temperature rise and spreads
> out any hot spots. It does not reduce the final, steady-state, average
> surface temperature. The thin-wall pipe will indeed have more prominent
hot
> spots. These hot spots will appear on the outside radius of the bends as
> they leave the engine, where you can see them easily.
>
>          It is probably be a good idea to use thick-walled pipe for the
> first several inches, and then transition to thin-walled pipe. I don't
> know, but I suspect that the stock manifold is quite a bit thicker than it
> needs to be, however.
>
>
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