My TT .91 weighs about the same as my ST .90, maybe a tad more. But then this is an older one with the bolt on bearing case, so it may weigh more than a new ST .90. My TT .91 weighs 26 oz, just two ounces more than my old OS .91, but a lot more power. That said I would consider the YS 110. But then again that engine probably has more power than I would use most of the time and it probably would eventually get swapped to a larger plane.