I've just got a large outlet at the bottom rear of my cowl, cooling is not an issue (os bgx 35cc glow)
I suppose the gas engine just does not make the revs.
nice to see this thread re started, my downer has been hanging in the hanger for too long now- time for a dust off and sorte.
see if you can get your hands on a gps to slip into the fuse-you've got 140mph to beat !