The distance of the piston of the engine from one extreme position to the other is called a stroke. Also called the itinerary. The length of the stroke has a direct relationship to the piston speed of the engine. As the stroke becomes larger, the piston speed increases and the mechanical loss increases. This directly limits the maximum engine speed. The formula for the average speed of the piston motion is: stroke * 2 * speed. In general, the average speed of the piston of the engine will not exceed 20m/s, regardless of the engine exhaust volume or operating speed range. The faster the piston speed, the more unfavorable the engine life.