I hope this attachment works.

It's an email from the late Paul Conner with images of his 'muffler' on
his SQ2000. If you factor in 'goodness' as part of the quiet equation,
Paul had it all over anything else I've heard in over 10 years of
watching (& hearing) rotary powered a/c except Dennis Haverlah, & he
cheats by using a Renesis. While his plane wasn't silent, it wasn't any
louder than a typical Lyc and it was much more pleasing to listen to
than a 4cyl Lyc (& quite a bit more pleasant than the 2stroke-like bark
of a typical rotary. It really sounded like a healthy automotive V-8.

It's also pretty hard to beat for simplicity and even weight. Obviously
cost a little HP, but real tuned headers + an equal performance muffler
would weigh several times as much & just might drive the HP back to
Paul's configuration. Run the HP vs weight gain vs money numbers....

Charlie