How to Determine CCs for a Motorcycle Engine

What You'll Need
Owner's manual

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: ((bore multiplied by bore, multiplied by stroke, multiplied by PI), divided 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 the bore by the same number as its measurement. So, as in the example above, if the bore is 60 millimeters, one must multiply 60 millimeters by 60 to get 3,600. Next, take the product of the first multiplication and multiply it by the 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 3,600 to arrive at a product of 252,000. This number must then be multiplied by pi (3.141593) because the piston cylinders are circular. So, 252,000 multiplied by PI would result in 791,681.436.

Step 3 - Divide

A red motorcycle.

The product of all the multiplication in the previous step must now be divided by the number of cylinders in the engine. Since the example only has only two cylinders, one would divide 791,681.436 by 2 to get 395840.718. Finally, divide the entire number by 1,000 which is 395.840718.

Step 4 - 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.