In an engine, the bore refers to the diameter of each cylinder). The engine displacement is calculated based on the bore, stroke length, and the number of cylinders). The stroke is the distance within the cylinder that the piston travels. The bore and stroke ultimately determine the engines displacement, and you can multiply that number by the total number of cylinders to determine an engines displacement. The stroke ratio, determined by dividing the bore by the stroke, traditionally indicated whether an engine was designed for power at high engine speeds (rpm) or torque at lower engine speeds). A bigger bore is generally the best way to get more power, as it creates more space, allowing for bigger valve openings, which in turn can bring more fuel and air into the cylinder. A bigger bore with a shorter stroke also allows an engine to rev higher, which creates more horsepower. On the other hand, a small-bore, long-stroke engine requires the flame to travel less distance during combustion, which means the burn duration is shorter, allowing combustion to do more work and make the engine more efficient.