Baobab, you have a good idea already. I can help a bit...
The Lycoming has a "ring gear", which is used for starter motor engagement, and alternator drive belt (and maybe prop deice), but really has no significant flywheel affect. The metal propeller is the flywheel. This I know because I did testing of an IO-360 equipped with a small diameter Hoffman four blade propeller. The engine ran nicely, but was miserable to start. There was only a minor flywheel affect from the smaller, lighter wooden prop. During a start attempt, there was no flywheel affect to carry the engine through the compression stroke, so it acted as though it had a flat battery, even though the battery was fine. Similarly, the MT props can be a little difficult to start on the Lycomings. I did many shut down, feather and restart tests on the MT & IO-360 equipped DA-42-L360. The MT made the engine very hard to windmill start, and there were times in flight where I had to starter motor start the engine, or would not have go it running. Larger diameter heavier metal props seem to windmill start better - once you get them turning over, they stay turning, so the engine can start smoothly.
I'll have a look at my Lycoming data, to see if there is a reference to thermal efficiency, I do not recall having seen it before. If it interests you, compare the Lycomin IO-360, and HIO-360. Though the same displacement, they have different compression ratios. The HIO turns faster than the IO, though their powers are the same, or very close.
The compression ratio has a relationship to the torque of the engine. Though torque is not employed quite the same way in an aircraft engine, as it is in a car engine, there still is an effect. You can obviously pitch the propeller to be more course, and extract more power at the same RPM. The octane requirement of the engine is a direct relation to the compression ratio, which is a factor in combustion pressure, and the prevention of detonation. Detonation is also affected by engine speed. More speed = lesser chance of detonation, all other things being equal.