The .55 AX is a great sport flying engine in pretty much any ARF designed for a .60, it will not 3-D a 60 size plane. It is a little under powered for a kit built 60 size plane, kit's are heavy compared to an ARF of the same size, something do do with the weight of wood compared to air and covering?? Up-Roars!!!!!!! I have built 8 of them, two or three kits and the rest I used my own wood and cut my own kits from templates I made from one of the kits. I love that little plane and the better looking Dazzler, they fly the same but the Dazzler is a better looking bird. I never stuck in a bigger engine then the OS .46 LA in any of mine, except for some engine break in's. I have flown a few I built for other guys with the OS .46 FX. It's a fun fly plane and just doesn't call for a bigger engine. Sometimes I think rubber band power would work on them, that's a heck of a wing they have!!! I no longer have an Up-Roar but I do fly a 60 size Hots, same wing design and will fly the same.