How engine size is measured

The size of an automobile engine can be measured in many different ways. Most of the ways that engine size is determined are based on its displacement. Other ways of determining an engine size are based on its number of cylinders.

The displacement measurement

Displacement is the most common way to measure an internal combustion engine. Displacement means the amount of volume that is displaced by all of the cylinders in the engine combined. This sounds complicated, but it becomes simpler when you break it down.

Finding the displacement of one cylinder

To find the displacement of one cylinder you’re going to need to use a little math. The displacement is determined by finding the area of the bore, and multiplying it by the stroke of the piston. This will give you the volume or displacement of the cylinder. The first thing you need to know is the bore and stroke of the engine. The bore is the diameter of the cylinder and the stroke is the distance the piston travels. To find the area of the bore, use the formula Area=πr2 where r is the radius of the bore. Once you have the area, you multiply it by the stroke to get the volume or displacement of a single cylinder. Once the displacement of one cylinder is determined you must multiply it by the number of cylinders to get the engines total displacement. Let’s do some examples.

engine size chart

Chart for determining engine size in cc.

Examples of finding engine displacement

A four cylinder engine with a bore of 50mm and stroke of 80mm would be determined like this.

The bore diameter is 50mm so the bore radius is 25mm.

The area of the bore will be 3.14X252.

The area is 1963.5mm2

The displacement is 1963.5mm2 x the stroke of 80mm.

The displacement then equals 157080mm3 or 157.080cc.

For a four cylinder engine you then multiply the individual cylinder displacement by four to get the displacement of the engine as a whole. In this example, the displacement for the entire engine would be 628.32cc.

Another sometimes useful thing to know is the displacement of one cylinder of an engine when you know the total displacement. To do this, you simply divide the total engine displacement by the number of cylinders. For example, a very common size for a V8 is 5.7 liters of displacement. Since this engine has eight cylinders, simply divide the 5.7 by 8 to get the displacement of just one cylinder. In this case, one cylinder would have 0.7125 liters of displacement.

engine displacement

The volume that all of the cylinders displace is the engine displacement.

How big is a 350?

Most American car manufacturers talk about the size of their engines in cubic inches rather than cubic centimeters or liters. A typical size for a General Motors V8 is 350CI or three hundred and fifty cubic inches. This engine ends up being 5.7 Liters, or 5700cc.

Is a V8 the biggest engine size?

Well, a V8 is a layout of an engine. The only thing calling an engine a V8 tells us is that there are 8 cylinders arranged as 2 banks of 4 in a V shape. The displacement is really what determines the size of the engine. There are plenty of large diesel engines that only have one or two cylinders that are much bigger than any automotive V8. Similarly, an engine designed as a V10 or V12 may not be any bigger than a V8 or V6 when it comes to displacement. There are many high performance supercar engines that are V10 and V12s that are only around 5 Liters of displacement. That’s less displacement than most American V8s.

Generally, all automotive engines will have 4, 6, or 8 cylinders. In almost every case, an engine with more cylinders will have more displacement. When comparing engine sizes, it is generally accepted that displacement is what should be considered and not the number of cylinders. If all other factors are equal (turbo, max RPM, compression ratio, etc) an engine with more displacement will produce more power.

Filed in: Gasoline Engines
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