A piston that is elliptical in shape when cold is termed a(n) _______ piston.

A piston that is elliptical in shape when cold is termed a cam ground piston because this design is specifically engineered to accommodate the natural expansion and changes in shape that occur when the engine warms up. The cam ground design allows the piston to maintain a better fit within the cylinder as it heats up, ensuring that it takes on a more circular shape at operating temperatures.

The unique geometry of cam ground pistons helps to reduce friction and improve the piston’s performance, leading to an overall increase in engine efficiency and longevity. This design is especially beneficial in high-performance or high-temperature applications where maintaining optimal contact with the cylinder walls is crucial for effective combustion and reducing wear.

In contrast to the cam ground design, options such as oval ground or two-piece pistons do not specifically refer to this unique elliptical to circular shape transformation associated with temperature changes. The term "truck type" usually identifies pistons designed for specific applications but does not relate to their thermal characteristics in the same way.