It's
an issue of burning the paint aft of the existing insulation blanket and above
the exhaust tip. Also, the strength of a carbon composite structural panel
is reduced while at elevated temperatures.
I happen to have just measured temps around
my LIVP exhaust to get a baseline for an alternate exhaust pipe. My stock
pipes are aimed down at a 45 degree angle, so it's about as cold as you could
get in the IVP installation. The hottest point I measured.....and
this was just going around the pattern, not at high cruise with the TIT
maxed...was right about 200. With a more streamlined exhaust I would
expect way higher.
I'm told prepreg epoxy starts to soften at
250 while high quality epoxy that we use for hand layups is down around 170
dF. (boat epoxy is down at 120 dF) Doesn't seem like a good match for the
fire wary. I recently got to observe what happens if you have a leaky
exhaust slip joint, for example. Having another layer of metal
nearby strikes me as a good idea