After reading posts about using the Tower Hobby muffler I tried in on a OS 46AX.

My flying time went from over 15 minutes to under 9 minutes. []

The Tower muffler has a small amount of additional power over the stock muffler and turns a 11x6 prop at 12,800 instead of 12,400, but it's not worth it to me. I would rather fly the additional 6 minutes!

My advice is stay with the stock exhaust. It's tuned for the engine and preforms better.