Which bore shape would NOT be found in a high-speed engine piston centerline?

In high-speed engine pistons, the design of the bore shape is critical for efficiency and performance. A crescent moon shape would likely create uneven distribution of forces and could lead to issues like poor sealing and increased wear, making it impractical for high-speed applications. High-speed engines typically require bore shapes that promote even wear and uniform combustion characteristics, hence the common shapes include round, oval, and occasionally square, as they can effectively manage the stress and strain on the piston, improve sealing, and optimize combustion efficiency.

Round bores are most commonly used due to their well-balanced performance characteristics. Oval shapes can also be designed for specific applications where certain performance traits are desired. Square shapes, while less common, may be utilized in specific configurations to achieve particular design goals.

The crescent moon shape disrupts these requirements significantly, thus it is not suitable for high-speed engine pistons.