I fly a 4*40 w/ an OS 46AX that is just now getting well broken in. The 46AX replaced an aging OS40FP. I run APC's 11.5/4 propellor. With the stock muffler, the 46AX flys the plane with authority and it's a pleasant sunday cruiser that does basic aerobatics quite well. But, it will not quite hover.

I bought Tower Hobbies muffler ($14.95 and reputed to be a cheap mod for performance) and the 46AX came alive. Now it turns the 11.5/4 prop at just over 13000 rpms. Top speed is scary fast for me as a fun fly lover and I spend a lot of time at about 1/3 throttle. The plane will take off into a hover in about 20 ft. and easily maintains the hover. It will not, however, pull vertical out of a hover. At 4200 ft. elevation, it literally has "unlimited vertical" and will accelerate in a vertical upline. That muffler made the plane into an entirely different animal that competes w/ my Hanger 9 Twist (w/ OS 50sx) for adrenalin rushes. I've achieved flat spins (though once started the plane doesn't want to stop), rolling circles, and high-angle-knife-edge flights with stock surfaces (only having the control surface gaps sealed). The motor did require addition of about an ounce of lead under the horizontal stabilizer for balance but it now flys as well inverted as upright.

I love the OS 46AX and the $14.95 for the Tower Hobbies muffler is money well spent IMHO. BTW - I've read in the forums the Tower Hobbies muffler gives similar results on the Thunder Tiger Pro 46.

Live long, and prosper
Jerry L. Gubka