The engines we fly today are fantastic compared to what was available many years ago. I have been running model engines since 1950, so I have seen the good and the bad.

40-50 years ago, engines with steel liners and cast iron pistons had to be broken in correctly or they wouldn't run well or last any time. Now, most people just drop the engine in and go fly. Doing this may not get you the best performance in the long run, but it does work due to superior metallurgy and quality control during manufacture.

Ringed engines take at least, a few rich runs to seat the ring. If you don't do this, you risk a poor compression seal and less than full power. Many people run these engines lean too soon and then complain that they have less power than a corresponding ABC engine. Once an engine is in an airplane, there is a great urge to lean it to max power no matter what the instructions may say. This may be one of the reasons that manufacturers produce mostly ABC engines, to make them easier for the novice.

As for power, unless you are racing, there is really no difference. Take the new OS .50, for example. It is a ringed engine, while their .46 is ABC (or ABN, however you want to call it). I think you'll find the .50, even though it is only slightly larger, is considerably more powerful.