I used to run mine with OS .46 FX also, but with a Nelson Ultrathrust muffler. It performed very well with this setup. I went between a 10x6 2 blade and a 9x6 three blade prop, which helped somewhat with downline braking- a nice thing to have when flying in boat-ridden coves. I have the copycat Neptune NIB that I bought years ago to replace it, just havent had the time to put it together. I was thinking about going electric this time though, since I fly from a boat and the logistics of fuel/starting equip can be a pain. That, or holding off even longer and wait and see if they come out with a suitable sized gasoline ignition engine for the Seamaster. Or do they already?