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
 
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