I agree that the 12.25x3.75 APC's are too dang big for a .46! I was never able to get my Prto .46 to run good with one. Either a bad idle, real sluggish transition, or a finicky high end.

The 11x5's are nice, but a little too small.

My favorite is the 11.5x4 APC. Just light enough for the throttle response and acceleration you need and gives you almost as much thrust as the 12.25... They look normal too.

I recommend the Tower Hobbies muffler. It will give you a very noticable power increase and seemed to make the engine easier to adjust. My throttle response is GREAT and I have never had a Pro .46 run as good as this one after I got the Tower muffler. Definitely the best $12 you will spend!