Sport_Pilot, Speedster,


In model, tapered-bore ABC/ABN/AAC engines, life cannot be quantified as a linear function of RPM.

In a ringed engine this is not so easy either, since though the ring does ride on the cylinder wall, it is not only the number of times it reciprocates, but also the outside load applied to it.

Only a small part of the force that pushes the ring against the cylinder wall is the ring's springyness.
Much more of it is compression and combustion pressures, that bypasses the piston crown, enter between the ring and the top of its groove and build up behind the ring, being unable to continue down, between the ring and the bottom of its groove, since the piston is pushing up against it, sealing it for all practical purposes.

So the higher the compression and combustion pressures, the harder the ring is worn against the cylinder.

So higher BMEP/torque may wear the ring as fast, or faster than higher RPM.


If anyone here does not understand what I just wrote, it is not because it is incorrect.
Just look closely at full-size, drag-race pistons, from some years back and the holes drilled in them, through the crown, to pressurize the ring grooves...


Back to tapered-bore engines; the pinch does not exist, when the engine is running at its normal operating temperature, so no vibrations will be caused by this 'cold only' pinch, neither will any additional wear take place.

The piston is actually riding on a film of oil and this is the reason RPM does not directly determine its rate of wear.

High compression does increase the vibration level somewhat (greater change in rotation speed) and may require more flywheel, or more RPM, to overcome, in a single cylinder engine.
The differences are not very large, however.