How to Determine CCs for a Motorcycle Engine

Anyone who has done any sort of work on a motorcycle engine has heard of the ccs. Cubic centimeters, or ccs, are the unit of measure used to describe the amount of air displaced in the piston chambers during one revolution of an engine. There are two important variables that determine how many ccs an engine has: the bore and the stroke. The bore refers to the size of the chambers in the engine that house the pistons. The stroke, on the other hand, is the distance the pistons move within these chambers. To determine the ccs of an engine, use both the bore and the stroke in the following mathematical formula.

Step 1 - Determine the Bore and Stoke of the Engine

Use the owner's manual to determine the bore and stroke of the engine. Both measurements will be given in metric measurements (usually millimeters). Specifically, the bore measurement will describe the diameter of the piston cylinder. The stroke measurement will describe the distance traveled by the piston from the top of the piston to the bottom of the cylinder head (when the piston is in the lowest part of its revolution). If these measurements are not in the owner's manual, some websites may have them.

Step 2 - Multiply

The equation for finding the engine displacement of a motorcycle engine is: ((one half bore multiplied by one half bore, multiplied by pi (3.1415927) multiplied by stroke, multiplied by the number of cylinders in the engine), divided by 1000. This equation assumes all measurements are in millimeters.

Since that may be a little confusing, the following will break this equation down step by step. To better understand the mathematics in the next few steps, imagine a motorcycle engine with a bore of 60 millimeters and a stroke of 70 millimeters. This imaginary engine has only two cylinders. First, multiply half bore by half bore. So, as in the example above, if the bore is 60 millimeters, one must multiply 30 millimeters by 30 to get 900. Next, take the product of the first multiplication and multiply it by pi (3.1415927) resulting in 2827.43343 then multiply by stroke of the engine. Again looking to the above example, if the stroke of the engine is 70 millimeters, then one must multiply it by 2827.43343 to arrive at a product of 197920.3401. This number must then be multiplied by number of cylinders. 197920.3401 multiplied by 2 results in 395840.6802 which is then divided by 1000 to result in 395.840.

Step 3 - Round Up

Last but not least, round up to finds the ccs of the engine. In other words, the engine in our imaginary example is a 396 cc engine.