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Scott Dahlgren's inquiry about the heat wrap tape brings up the point of
possible heat backloading of the   exhaust valves. While I know  NOTHING
about aviation engines,  I have experience with smaller air cooled
engines.  Often, when installing an aircooled generator in a vehicle
(such as an armored car) we must heat wrap the custom exhaust that is
plumbed to the outside the vehicle.  Dependent on the makeup of the
valve material, (READ "STELLITE"), we have seen incredible  exhaust
valve overheating from backheating.  This may be less important in your
aircraft installations, as you should not have the more extreme changes
of direction of the exhaust that we are force to use in our industry.
We find a "POINT AND SHOOT" thermo scanner made by Ray-Tech to be very
useful for determining the before and after effects of the heat wrap.
Thjis scanner is used by the builders of hi-performance engines, and by
"DRAG" Racers to ensure the correct temperature of their tires, engines,
exhausts, etc. I would also suggest contacting Lycom/Conti for their
experience/heat load limits for  the sake of longevity and safety.  
Regards to all,  build and fly safely,  Jeffrey B. Chipetine