Lee,
Guess I misunderstood....That's something to look into but after looking at Dick Pettit's cub with the same engine I see no enlarged exit hole. I have pictures of other DPM cubs and see none there either? Perhaps Dick Pettit can better answer that question.

I hear you on the early morning flights....what I liked about that time of day was the tails of F86's sticking just above the fog on the runway and you couldn't see the rest of the plane, talk about a picture!