One other thing to Ponder. Keep the overall weight of RTF plane to a minamum. All my Profiles over 7lb. I run the OS 120 2cyl.
The OMP kit built Yak54 RTF weight was 7lbs. 2oz( OS 91FX APC 15X4W) The New ARF OMP 65" 55-SP Yak RTF weight came out at 8lbs. 4oz so it received an (OS 120 2cyl. APC 16.5X5W) both sport stock mufflers. IMHO a stock muffler works the best for 3D.The Ultra Thrust mufflers such as the one from jett enginering is designed for racing (TOP END power and do not transition well when hovering) one thing I do not like is a plane that will only hover just under full power. I like a plane I can tail slide in from 20 feet at a good decent and stop the tail slide where and when I want. This requires a very high power to weight ratio of at least (2 to1) another thing I like to do is start at one end of the runway at about 30 feet in knife edge. drop to 2 feet and fly down the center line of the entire length of the runway, high alpha knife edge all the way The main thing is to get out and fly, fly, fly and experiment, experiment experiment OOH YEH remember Altitude is your friend when doing these things. LOL!!! P.S. The Goldberg Extreme 540 Extra 47" pictured here has an OS 91 FX (APC 15X4W) on it, theplane is in take off mode, the other is a 47" MVVS, SU-DO-KHOI with an OS 61 FX (APC 13X4W) Accel Katana Saito FA 72a (Zingar 14X4)