<<I was wondering more about the temperature of the plastic shroud
itself.
Being very close and directly above the cylinder heads  I assume it
would
get very soft during a hot soak.>>
Gary,
I did consider this.  A few comments:
The plenum cover is really closer to the cowling than the engine.  It
is not bolted directly to the engine so heat transfer through conduction
is not a issue.  I post-cured the epoxy plenum before flying by heating
up the engine on the ground and letting everything cool down.  My
observation is that the part remains much stiffer at temperature than
did the original cowl, which was made of polyester resin.

Two small plenums is another approach.  The one piece top was partly a
matter of convenience as the stock aluminum baffle structure was already
available for mounting.

Regarding "RTV BID".  I remember the post but forget what the
application was.  I have something similar covering the front spark
plugs.  The 360 cowl is very tight and where the front spark plug wire
loop around they nearly reach the cowl.  I had to make two little
flexible covers to give the front spark plug wires extra room.  They are
silicone impregnated FG.  I used a two-part room temperature cure
silicone.  It is a less viscous than RTV out of a tube and can be
applied with a brush.

Chris



Christopher Zavatson
Mobility Technologies
United Defense
(408)289-4329