When I bought the muffler I asked the Jett folks which muffler would give me more torque. I asked about the Jett Sream and the turbojett. The turbojett would have been a lot easier of an installation bc I wouldnt have had to carve up the belly of my plane so much.

The folks at Jett told me my best bet to increase torque would be the 120 sized muffler on the ST90 as oppossed to the 90 sized muffler.

So I went with their recomendation.