[David Paule]

For you folks trying to get your airplanes to go faster, what have you provided for the cabin ventilation air to exit?

Dave

 

[F1Boss]

easy

I added a bluff body outlet where the aft inspection panel is normally mounted. Seem to work OK for me - you could install such an outlet on the underside of the fuse near the tail if desired. Might think about a doubler around the hole you would cut if you pick this option.
For an example (sizing and design), have a look at any Beech 18.

Carry on!
Mark