sharkey,

I have the same setup except for a Tower Hobbies muffler. I quick get it going prop would be 11x4 apc. Kevin's 11.5x4 would be good to.

In the past I would run the 12.25 x 3.75 and Paul S. said to try the smaller diameter as the TT like higher rpms, (I hope I got this right, sorry it's from memory). It did work, quicker throttle response also. I just got some 11x4 Zingers and need to try them. The weight difference is huge so it should be interested.

Remember we are talking about small differences here so don't get to worked up about this, (just don't put an 10x7 on that plane).

Have fun.

Ken