How to Determine CCs for a Motorcycle Engine How to Determine CCs for a Motorcycle Engine

What You'll Need
Owner's manual
Calculator

Anyone who has done any sort of work on a motorcycle engine has heard of cc's. Cubic centimeters, or cc's, 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 cc's 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 cc's of an engine, use the 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 post them online.

Step 2 -  Multiply

The equation for finding the engine displacement of a motorcyle 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 also, has only 2 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 3600. Next, take the product of the first multiplication (3600) 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 3600 to arrive at a product of 252000. This number must then be multiplied by PI (3.141593) because the piston cylinders are circular. So, 252000 multiplied by PI would result in 791681.436.

Step 3 - Divide

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 2 cylinders, one would divide 791681.436 by 2 to get 395840.718. Finally, divide the entire number by 1000. 395840.718 divided by 1000, leaves only 395.840718.

Step 4 - Round Up

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

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