Hey Dan,

The engine is now in a 30 size Yellow Aircraft Sukhoi, weight is 73 oz with 21.4 oz wing loading. I made the muffler out 1" dia. aluminum bar stock and has an internal diameter (I.D.) of 7/8". Length is 2" with a 6-32 pressure fitting. The 90 deg. outlet on the can is .350" O.D. x 17/64" I.D. x 1/2" long to fit a Dubro silicone exhaust deflector.
I made a 90 deg. header pipe out of steel with an I.D. of 19/64" (.298") from the stock 6.5MM (.256"). One end was threaded to match the M10 x .75 thread of the engine head and the other end was 3/8-24 to match the muffler. The weight is less than an ounce more than the original. I would conclude that the larger volume and pipe I.D.'s was the gain to the RPM increase. Sorry, I can't attach a pic.
As for Props, I just ran the APC 12 x 6 on the ground for now. I have yet to fly the plane (hopefully this weekend). The 11.5 x 6 Bolly works very well and have used them in the past. It feels like it has more pull than the APC, but a test fly is in order there. I have also used Zinger 12 x 5's in the past which worked alright.
If you want a prop for hovering, use the largest diameter, smallest pitch possible. I do have 12 x4's (probably not enough), I don't have a 12.25 x 3.75 (probably O.K.) or a 13 x 4 (???) to try.
The problem with swinging to large of a diameter prop on a 4 stroke is that it tends to load up the engine and you get detination.

I'm certain this engine is now turning RPM's very close too, if not more than a .46 2c swinging the same sticks! I'll have to bolt the two on my FX and compare?


Happy Fly'n....