I have had several of these planes. A good strong .46 engine will work just fine. I believe the Tower .46 muffler will fit that engine. I had an OS .46 FX on my current UCD, using a Tower Muffler, 15% Byrons and either an APC 12X4 or 13.25X3.75W prop, it worked just fine and hovered reliably. Once I wore the .46 out, I installed a Magnum .52 with the same Tower muffler. That engine is nearly worn out as well, but still under warranty. The plane rocks with this engine. Sean's advice to avoid the .61 is good advice, not only is that too much engine, the wing loading would suffer due to all the weight you would need to add to the tail to balance the plane.

I used an OS .50 SX on mine for a while and it worked pretty good, but like the Magnum better, once I got it broken in. Many members of my club are using the OS hype .50's on thier's with 20 to 30% nitro. They really rock and spin an APC 12X4 well over 16K, hover about 1/2 throttle and have unlimited accelerating vertical.

If you consider a 4 stroke, a Saito .91 or .82 is the way to go, due to them being the lightest of the class.

There are several threads about this airplane on the 3D and sport areas that you might want to visit.

You also may want to set up your account to take PM's.

Hope this helps, You'll love this great airplane, make sure you read up on the landing gear fixes also, If you fly aggressively off of grass and do harriers, you will be repairing the landing gear.

Happy Landings!