The reason displacement is so important in engine design is that in general there is a direct relation between the amount of displacement, and the amount of power ultimately produced by the engine. There are a lot of other factors, but as the old saying goes: “there’s no replacement for displacement!”

Just like when measuring the internal volume of any cylinder (like a can of Cola, which is 355cc by the way), displacement of an engine is determined by the bore size (diameter) and stroke length (depth). Bore size is simply a measure of the piston diameter. The stroke length is how far the piston itself travels inside of the cylinder. For example, the standard bore of a 150cc GY6 piston is 57.4 millimeters, and the piston travels 58 millimeters within the cylinder every cycle.

The more displacement an engine has, the more air and fuel mixture it can suck in from the carburetor. The more gas and air you can confine into a space and ignite, the bigger the boom! This translates to more power at the wheels of your buggy. The internal volume of the engine can be upped by either increasing the bore or the stroke sizes. While these both do the same thing, they are not created equal. This leads us to the next point…