here is an OS 45 FSR with stock muffler and the DuBro "diverter".
It really runs hard on a 10x6 TF and #1 Magnum fuel.
power loss ? not much, if any .
Very quiet in the air and flawless performance even if the old bearings are starting to sing a bit.
I have not run one of these engine in years , but tuning was easy and in the NOBLER- it was very fast --or- flew slowly with instant acceleration.
If you are having trouble with this type diverter - something else is wrong in your setup .