RE: SAP 180 (Syssa Performance)
I have seen Walt Erickson's Aquila set up with a SAP and the stock muffler.
Surprisingly good combination! He is using stock components and also an ignition battery and switch instead of the IBEC, so his model is a bit heavy on the wing loading, but it still flies great and makes weight easily because it is not a full 2-meter ship. I think the wingspan is around 70 inches and weight is probably about 9-3/4 lb.
Very little, if any, cutting of the cowl to accommodate the Pitts muffler, and noise level is very well controlled with the muffler "tone inserts", as Syssa refers to them, with very little loss of power.