Piston speed is a phrase found primarily within engine building discussion groups. This terminology refers to the average speed, measured in feet per minute, of a piston moving through its combustion cycle inside of a cylinder or, as it is more commonly referred to, its stroke. The formula for determining average piston speed is: (RPM x 2 x stroke)/12.
Engine designers refer to many factors, including piston speed, when designing a new engine. Functions such as oil pump volume, piston ring design, and engine cooling all work in concert with the function and cooperation of the other engine parts. These factors also help in creating the parts to ensure that they are comprised of the proper materials and the proper thickness to withstand a lifetime of duty within an extreme environment.
When creating a new engine for a production vehicle model, factors such as piston speed help in determining where the engine will make its peak power and efficiency. Fuel mileage and towing capabilities are all determined by these different engine characteristics, as are fuel type and octane rating. In aircraft engines, even maximum altitude restrictions can be influenced by piston speed.
A combustion engine is nothing more than a big air pump. The efficiency of the engine's ability to pump and move air is the determining factor of a successful engine. While pumping its air, an engine creates heat from the friction of all of the moving parts. The designers and engineers put in many long hours designing oiling systems that will cool the engines and allow them to perform their job under less heated and damaging conditions. They examine all aspects of the engine during this critical design phase.
In performance applications, piston speed is a critical factor in determining fuel mileage. It appears that more and more races are being won by a vehicle with the lowest fuel consumption per mile (kilometer). Therefore, it is the engine designer's duty to create an engine which will make the most power while consuming the least amount of fuel. The remainder of the race vehicle is often built around that engine design.
Piston speed is responsible for the ultimate creation and success of any given type of vehicle. Long hours are spent calculating component design and the relationship of those components to other engine parts. Piston speed is a critical component in combustion engine design, planning, and execution.
