Q-ball, Im useing a K&B .61 with a 13x6 prop, and yes it was a lot of trouble to get it in the plane the way i like it. I always try to center the muffler or tuned pipe between the landing gear it looks better and keeps the oil spray on the bottom of the plane. i had to cut a half circle out of the bottom of both firewalls and use balsa sticks to build an inclosure along the bottom of the plane where the tuned pipe ran this was done to the belly panel to. the two black plastic wing things are used to take up space where the wings but up against the fuse, without them on my plane i could see a lot of gaps between the wing and the fuse i also didnt use most of the hardware that came with the kit like the aluminum moter mount it looked heavy and cheep so i used a nillon moter mount instead. The K&B .61 is a well broken in moter that has been one of my most reliable engines. to date it has never even dead sticked even when it was new and breaking in im shure its all about High RPMs as to why it makes this plane fast this engine makes every plane ive put it fast , so long as the planes weight stays in the 5- 7 lbs range. but when i put it on the Edge the shape of the edges wing made it fly faster than enything that ive flown before that might not be saying much tho. the bad part of this story is that i didnt want a fast pilon racer i wanted a 3D plane and this plane is to heavy for this. The elivator and rudder throws are to limmited in their travel do to. The angles where not cut near the hinges to allow larg throws. i know i can cut o n the covering and redo the hinges myself but this would ruin the looks of the covering and the plane would no langer have this great looks it has now. so im keeping this plane the way it is and ill fly it when is want to fly fast but when if want to fly 3D ill fly my new Funtana 40 that just came in yesterday.