So the area ratio is 1144/1255 is .91. Not much.

     Calc the new area. 6.28 times .91 is 5.72 square inches.

     5.72 divided by pi is 1.82.

     The square root of 1.82 is 1.34" radius or 2.69" diameter pipe.

     Might as well use 2.75" inch pipe. Well it is a little bit
smaller.

     You would have to lose a lot of temp to make a big difference.
     That lost heat would wind up under the cowl.

     Paul Lamar

Paul and Jerry,
Jerry's cool pipe through the muffler will help in that reguard. The
best solution though would be to vent the cool pipe overboard as
well to prevent heating the cowl air.
Bill Jepson

Bill,  there is no problem with venting the cool pipe overboard.  I
plan to do that except when I am using it for cabin heat.

Careful on that Jerry. You could get carbon monoxided.  A little
un inspect able crack and you would never know what gassed you.

Paul Lamar

It is no different than any other heat muff in this regard.  I don't
see it as a real danger since the cool tube is protected from burn out
by a steady stream of cool air.  Still,   it is something to consider.
  Either way,  the hot air will be not be dumped inside the cowl.
Jerry

The heat muff on the C182 can be inspected. It is bolted on. When it is unbolted
you can see if there are any cracks in the muffler can. With a tube welded into the
muffler can that is not possible unless you use something like a bore scope or pressurize
the tube and see if it loses pressure. CO is odorless so you would never know
you were being gassed. The best heater is a duct on the back side of
the oil or water rad that picks up hot air from that source.

Here is what Dave Leonard is using.

Paul Lamar
 
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