Flyboy, I believe if you take the time to read back through the pages of this thread, you will find that engines ranging from the OS 1.60 all the way up to the DA 50 have been installed in this plane. And, I think if you read in between the lines, you'll find that all of these different engines have their advantages and disadvantages for this airframe. The OS 1.60 is plenty of motor, but from what I've read, most of the guys who installed this motor ended up moving servos and stuff around because the plane ended up on the tail heavy side. Notice I said "most"-apparently for some others, it wasn't a problem. In doing my research, I contacted someone who had installed one of the early DA 50 combinations in his Cap-X, and he told me that the plane flew OK, but the wing loading was too heavy for some of the 3D stuff. He advised me to stay away from this combination for this airplane. However in John's review for RCU, he loves the way his plane performs with the DA 50. I honestly think it's more a matter of personal preference and each individual's particular flying style. Over time, I've seen so many reports on the same plane/engine combo, where one guy loves it and another guy says it's a piece of junk. Go figure.

I'm with you on the Saito engines. I have three of them in various sizes and really love them. However, again as part of my research, I found that the bigger Saitos were quite thirsty and would be rather expensive to operate in a plane this size. Again, this is a problem for me, but may not be for others.

I ended up choosing a Moki 1.80 for my Cap-X, based on what I read right here in this thread. I can only tell you from my personal experience what to expect if you choose this motor. Sizewise, it fits perfectly. You do have to redrill the holes for the motor mounts, but it's no biggie. My airplane balanced right on the recommended CG without any balast or moving anything around. I used Futaba 3050 digitals on all control surfaces with the exception of the rudder, where I used a Hitec 5625. I have a 2100 ma 6V NiMH battery mounted very close to the CG. I bought a 580 cc Tettra tank due to the capacity needed for the bigger Moki. One nice thing about the Moki is that it runs just fine on FAI fuel, which has 0% nitro and costs me around $7.50 a gallon. I just throw in a little extra Castor Oil and I'm good to go. It starts on the first flip every time-you don't need an electric starter with this motor. Just break it in as they recommend in the instructions. Idles great, plenty of power for this plane. There are three or four of them in my club and all the guys love them.

Again, if you really want to answer your own question, just take the time to go back through this thread and see what others have written about this very subject. I think the OS 1.60 is a fine choice, as are many of the others. You just have to decide what the important points are for you and go from there. 2 stroke, 4 stroke or gas, they all will work.

By the way, I'm kind of surprised that this plane has not become more popular. I have not read many negative things about it. It seems that Chip has designed out a lot of the bad Cap tendencies. It's an awesome performer in my opinion. It flies much better than I can, and has provided me with a great 3D learning platform. About the only negative thing that I can think of is that the wing is a one piece design, and the sucker is big. Makes transporting it somewhat of a problem for people with smaller vehicles.

Good luck with choosing your motor,

Vince