Hi Pe
That's pretty much what I'd always thought until I started measuring and collecting some figures which is why I said I can't find any rhyme or reason.

As a for instance, compare my Moki M5 with my Enya 60-IIIB. Both are 60's, both baffled piston, both designed for low down torque and both have identical cylinder timing. But the crankshaft timings are radically different. The Moki (and the Magnum GPA 53) has by far the most conservative timing of any of my engines at 45/30 while the Enya is 40/55. The Enya has identical crank timing to my Rossi 45. So there's 2 engines ideally suited for CL stunt yet one has the crank timing of a high speed engine.

Another comparison in the RC sport type where the Rossi can be used as the bench mark at 40/55. The Magnum 46XL is 35/50 (same duration but 5 degrees earlier open/close) but with far more aggressive cylinder timing. The ST G51 though has a very mild crank at 43/40, far less duration than either of the others but it's certainly no slouch.

I'm confused .