RE: Anyone tried an oval outlet pipe?
No, its not stock, its just an experiment which was done to minimize losses with a RAM 500. -Instead of the bifurcated pipe, I made a single wall oval exit pipe.
now with the rabbit power is plenty , but I left the single pipe as it works well.
I made a plywood former (as in your drawing) to fit the pipe oval exit, no need for a strut..
the plane is in storage now, but can get some pics for you later if needed.