For those of you still flying the OS.46fx here are some bench readings with the jettstream muffler in case your interested. (This is a rather worn out FX so one with less miles would probably do better).

Omega 15%
OS #8 plug
APC props
OAT 85 degrees F
Humid conditions

9x8 15,700
10x6 15,100
10x7 14,500
11x6 13,500 (never really got on the pipe, this engine likes to rev)