Posted for "Steitle, Mark R" <mark.steitle@austin.utexas.edu>:

 Chuck,
 Yes, I do believe I've got it covered.  I can see your point though.  If
 the exhaust is hidden behind and under the engine, the UVtron would have
 trouble "seeing" the fire until it was a full-blown emergency.  My
 situation is a little different as my exhaust headers all exit straight
 out the left of the engine (Mazda 3-rotor) and then down and back,
 exiting through the tunnel.  The UVtron, which has a 180* viewing angle,
 directly faces the exhaust system since I rationalized that if there was
 a fire under the cowl, it would most likely start in the vicinity of the
 exhaust system.  If there is a crack in the exhaust, the flames would
 start escaping out through the split and the UVtron would alert the
 pilot within a second or two.  If for some reason the flames aren't
 visible through the crack, then the crack would most likely continue
 getting bigger until the UVtron was able to "see" a wisp of flame
 peeking out through the crack.  It really doesn't take much flame to
 trigger this device.  The UVtron can "see" a flame the size of a match
 from across the room.  So, it doesn't take much to get its attention.
 It sure beats the fire warning system I had before (nothing).
 
 Thanks for asking...
 
 Mark S.