I presume you mean the 61CX which seems to be based on the 50CX seeing that the stroke is the same for both of them. The .61 really is a .61 though. I have the 61CXLRS which is just the rear exhaust version of the CX (the extra "S" at the end just means it's the CL stunt version). I'm extremely happy with it, although obviously I can't comment on an RC application, and has never given a moment's trouble in the (so far) 7+hours of running. Being a ringed engine it needs a typical Enya fairly long running in time. The Enya web site shows it as being an ABN liner but not to fret. The instruction sheet gives a bit more detail and it's actually a Nikasil liner using a silicon carbide composite which I think is a first for model engines. It seems to work OK in Formula 1 race cars anyway .

Granted that my particular use is different to RC but mine swings a 13.5x5 Bolly FG prop with ease (WAY too much power if it 2 strokes) with zero nitro fuel but a lot of oil because I want it to last forever . At about 12 ounces bare for the RC version it's a real lightweight compared to other .60 size RC engines.