Which factor influences power output at a constant displacement?

The factor that influences power output at a constant displacement is the compression ratio. The compression ratio is the ratio of the cylinder's maximum volume to its minimum volume and plays a critical role in an engine's efficiency and power production.

A higher compression ratio typically allows for better fuel atomization and combustion efficiency, which leads to an increase in power output. This is because, under higher compression, the fuel-air mixture is compressed more before ignition, creating a more powerful explosion when ignited. It results in more complete combustion of the fuel, thus maximizing the energy extracted from it and converting it into usable power.

While factors like piston stroke, intake valve size, and fuel quality can also affect performance, they do not serve as direct influences on power output in the same manner that compression ratio does when displacement remains constant. Piston stroke affects engine displacement, intake valve size influences airflow and performance, and fuel quality can impact combustion efficiency, but compression ratio specifically ties into the engine's mechanics with regard to efficiency and output power in the defined context.