Are 4-strokes not a good match for this airframe? I noticed that the Thunder Tiger F-91s is actually about 3 oz lighter than the Thunder Tiger Pro .61 2-stroke. I was actually leanining toward the TT F-91s for mine (I have a brand new one sitting around looking for a home), but a Super Tigre G-61 or Thunder Tiger Pro .61 would seem to be a more popular choice for this airframe.