Mark,
Take a look at the newest Mistral pictures. They are using a tangental with a "cool tube" something that I drew several years ago for PL's site. They use a large down pipe with a annular exit around the tube. If you are doing something new it is worth a look. Material is 321 I think.
Bill Jepson

 

Hopefully it is an improvement on the last years model made by a third party, that decomposed and blocked the outlet, bringing the test plane down.

 

Muffler design is very serious business.

 

Lynn E. Hanover