The 120 size jett-stream is a good solution for a torque install. That muffler boosts well from about 10000 to 13000 rpm - lower range than the 90 size muffler - so its better if you are running larger props.

The turbo-jett has a bit different torque boosting characteristic, especailly with the big engines. Plus I prefer it on the in-cowl applications.

Gringo, what size props did you utilize?

reference here... this is a large Pitts with OS160 and turbo-jett. Again, visualization of how one installs.