Definitely not my intention to start a heated debate. You are 100% correct about the OS. My point was based on observance of the OS FX 1.60 on H9's 1/4-scale Cap 232 -- a very close cousin to the H9 Edge 540. While that engine provides all the power in the world you would normally want for a 1/4-scale aerobat it lags behind the Moki 1.80 and 2.10. In addition, I wouldn't mount anything less than the OS FX 1.60 on a 1/4-scale plane designed to fly the 3D envelope. That is why I said the OS FX 1.60 is on the low-end of the RECOMMENDED power.

RECOMMENDED = pilot's recommendation, not manufacturers.

BTW, I would be the last person to denegrate the OS FX 1.60. I've been getting max out of my 120 Ultra Sticks on that engine for the last 3 years -- I only hope that my 1/4-scale Cap will give me the same dependability with its Moki 180 that I've had with the OS. I would even recommend the OS over the Moki if it could be mounted without having to add extra weight to the nose because pound-for-pound it is slightly more powerful than the Moki(s), i.e., 3.7hp for 32.6ozs vs 4.1hp for 41ozs vs 4.95hp for 46ozs.

Besides, I have another 120 Ultra Stick in a box with a choice of a Zenoah G23 or the OS FX 1.60 (The G23 is a dog on this airplane, therefore I will stay with the FX 1.60). I also have a NIB Moki 180 and a H9 1/4-scale Cap in a box -- a marriage made in heaven.