When you level off the fuse, the 14" will not clear. the 12" was cutting it very close (on grass at least...pretty good chanceit will work on asphalt). But the .91 does not fit on the engine mount either. You would either have to get a new nount or modify the stock mount. Besides, it's a 6 lb plane. I think a .91 would turn it into something just short of a missle. And if the wings don't hold up, you will have a missle. Those aren't fun, I've had that happen before.