I am in the process of training a guy with a 46 FXI on his Nextstar. I have a 46FX and the engine is a rebadged 46FX. This is my personal opinion with no facts, but the engine runs very well. There may be some differences internally but overall it is a rebadged FX or it could be a modified AX (except for the head bold # and muffler). I removed the needle limiter and it is a normal FX now to me. High Speed and low speed adjustments are made the exact same way as my 46FX. The limiter is for a newbie not to be able to get the engine in a too rich or too lean situation, but the engine needed to be broken in and it was not broken in and needed to be adjusted badly. I had a 46fx on my trainer when I started and the FXI has the same exact pull as my 46FX had on my trainer. Yesterday, I did some training on a Nextstar with FXI and an Alpha with the Evolution 46. There is a very big difference in power. The FXI had a ton more power compared to the Evolution. The Evolution 46 did not have the power to accelerate into the air quickly. It literally creep on up in altitude, but the FXI really gained altitude quickly. Much more pull. The alpha did have a 3 blade and the Nextstar had a two blade, but the difference was significant. If OS ever starts selling this FXI engine seperately, I would by one especially if it is cheaper than the FX. It has the same power as a FX. I doubt they will ever sell the FXI seperately because people wouldn't go buy a higher dollar FX line then but would be bascially getting the same motor.