[aerohead]

* Pistons are formed out-of-round at room temperature.
* During operation, the piston/skirt expand, based upon the coefficient of thermal expansion chosen by the engine designer, becoming 'round' once thermally-equilibrated.
* The action of the piston rings under combustion pressure, staggered gaps in the compression and oil rings, along with the oil film separating the piston from the cylinder wall provides the trifecta of industry-acceptable combustion gas sealing.
* Compression ratio, rated brake-horsepower, and brake-torque reflect the capability of this trifecta.