Engine displacement

When you talk to bug guys for a while they frequently throw our engine sizes in CC's. You hear numbers like 1585, 1776, 2110 ... So I wanted to figure out how to calculate the size of an engine. Here is what I found out.

Engine displacement is a measure of the volume of air displaced by an engine. The measure of the distance between piston's top dead center (TDC) and bottom dead center (BDC) is known as the stroke. The measure of the cylinder diameter is known as its bore. Knowing the bore and stroke of an engine and the number of cylinders we can calculate the amount of air/fuel the motor displaces or its' displacement.

The formulas for a cylinder is given as:
Displacement = PI * BoreRadius^2 * Stroke * NumberOfCylinders

For my stock 1600 DP engine, this is what we end up with;

PI = 3.1428
Bore = 85.5 mm
Bore radius = 42.75 mm (85.5 / 2)
Stroke = 69 mm

Now for the math for my stock 1600!
3.1428 * (42.75 * 42.75) * 69 * 4 = 1585.25 CCs

Here are the common air cooled VW engine sizes (bore * stroke)
85.5 mm * 69 mm = 1585 (called the 1600)
87 mm * 69 mm = 1641
90.5 mm * 69 mm = 1776
92 mm * 69 mm = 1835
94 mm * 69 mm = 1914

A stoker motor has a crank shaft that has a larger diameter, which means the piston travels farther with each up and down stroke.
Stroker engine sizes :
90.5 mm * 74 mm = 1904
90.5 mm * 82 mm = 2110
92 mm * 82 mm = 2180
94 mm * 82 mm = 2275
94 mm * 84 mm = 2332