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?

Hi Tommygun,

I don't have enough info.
The un-piped 90 will have about the same ponies as the piped 60, but at different RPM.
Try running an 11-10 or 11-11 rather than the 11-7 you probably had onn the old piped 60.
Is that what you had on the piped 60?

Like I said ... need more input!

Dean P.

I think the old .60 had an 11x6 on it. When I got the .91, I somehow managed to put the recommended 12x7 or 8 on it. But, I moved shortly thereafter, and haven't been able to play with prop sizes for a while. (I'm just now getting ready to play with it again.) My LHS has a Macs header for a .91 FX, and a 15CC pipe. The pipe looks like it might be the right size, but I really don't know. So keep the original diameter, but go up in pitch?

I use a 13X10 or 14X8 or 14X6/8 on my 91FX will pull a 8lb bird almost out of sight. This is a long stroke motor that doesn't need the high rpm of the 61FX to do the job.

Taildrager, what kind of rpm do you get with the 13x10