Possibly of interest, piston rings are the single most important, and largest, source of friction in an engine.
With that in mind, simple geometry dictates that, other things being relatively equal, the
less piston ring "swept area" and engine has, the more efficient it will be.
Engine designers have known this since the very early days. A large piston+cylinder has less "swept area" than multiple small cylinders of the same displacement, or more correctly, power output.
Conclusion: One main reason old aircraft engines had such large pistons was that the piston ring swept area was as low as possible, to greatly improve fuel efficiency and therefore, aircraft range.
It's interesting to note that the best of these old engines were so efficient, Toyota only recently surpassed the 40% efficiency numbers. Same goes for the "airlines" with regard to "passenger miles per gallon". We've only recently "bettered" the pax MPG of the old piston powered airliners!
Piston ring swept area is one main reason!
Modern engine designers strive to use "low tension" piston rings everywhere. It help efficiency greatly. Unfortunately, sometimes the engineers go too far and the rings fail to seal after short periods of time and seemingly insignificant wear rates. Honda/Acura and the Prius come to mind. This often leads to high oil consumption.