I've been flying my Excelleron 50 for a couple months now and I love it! I am just a sport flyer but I like to make up my own pattern and fly the plane rather than let them fly me, if you know what I mean. My Excelleron 50 has had an OS FL-70 during most of that time but i recently replaced it. I think it was getting messed up somehow by the weird soft mount system that comes stock in the ARF. That stuff seemed to let my engine vibrate more than hard mounts, and seemed to shake the engine to death. Anyway, that is another story, and I just in the last few days put a Surpass 70 II in the plane on hardwood engine mounts. I hated to add weight (about four ounces all up) compared to the FL-70, but my son has the same engine and it runs like a champ all the time. I just got done installing it and will fly it this weekend. Prior to this, the engine could slow down to a walk to land, yet really zip at full throttle. There's some coupling caused by the rudder in KE, but I have gradually mixed it out with some elevator and aileron. Great airplane, my fave now, even over my CG Ultimate bipe with an OS 120 Surpass in it. BTW, my all up weight is 6.6 pounds with the heavier Surpass II in it. (I weigh the plane with me with my human scale, weigh myself again immediately, and take the difference.) Some of the trim covering needs to be CA'd down because pointed edges on the stars and other areas want to peel up. Oh, the FL-70 gave the plane unlimited vertical as long as you controlled the assent with rudder and elevator, while the engine was newer and strong. I expect the Surpass II to do the same if not better. Good flying, Jon