I have a .91 FX in a Sig King Kobra after breaking the connecting rod in my piped .61 FX. The motors are the same dimension wise, so it bolted right in. Well, I wasn't overly impressed as it doesn't have that high revving feel of the .61. It kinda sounds more like a slow chainsaw motor or something, and the plane flies accordingly. Granted, I don't have a pipe on it like I did on the .61, and I'm using a wider prop, so I'm hoping that could be part of it. Does anyone use these motors in pattern ships? Or should I go back to a .60?