Hi Alan,
Ringed engines are a pain, they are always wearing out and losing compression, just when you need it. If I were a serious competion flyer, I would do anything, rather than have a ringed motor. OK, they are easy enough to take down and hone the bore and fit new rings. But they always seem to play up at the most inconvenient time (in my experience anyway).
I think it significant that none of the top stunt motors, like the Randy's PAs, RoJett etc are ringed. They have gone that way for reliability. I still love my Merco 61's and think they are great stunt motors, but that doesn't fool me about their reliability at the crucial time. They can be an absolute pain , suddenly the run characteristics will change and you just know you have ring problems. Look at what the top fliers use. They were quick enough to drop the ST46s and ST60s, when they had the chance to go to reliable, repeatable ABC motors (or derivatives of the same)!
Right, I am going to dig a very deep foxhole. I rekon that I am going to get a lot of flak over this!
Regards,
Andrew.