Good question - How do you calculate the displacement (like "it's got a 5 liter V8!") of an engine?

by | Jun 14, 2010 07:30 AM ET

When you buy a car, you always hear about engine displacement. For example, the Brain Family's minivan has a 3.8 liter V6 engine. The Bugatti Veyron has an 8 liter W16 engine. But what does 3.8 liters mean, and what does it tell you about the power of the engine? The following video shows you how displacement is calculated in a very visual way:

The formula:

stroke * (bore / 2)^2 * Pi * number of pistons = total engine displacement

Here is more detail on what the engine is actually doing with that displacement:

See also:

How does displacement affect the power of the engine? The maximum amount of power an engine can develop is controlled by the amount of oxygen that can flow into the cylinder on the intake stroke. You can put all the gasoline you want in a cylinder, but the amount that burns is controlled by the amount of oxygen available. The larger the displacement, the more oxygen (and therefore the more gasoline) the engine can burn on each firing of the spark plug. The amount of oxygen is directly controlled by the engine's displacement.

The displacement, along with the maximum RPM, tells you maximum horsepower possible. There are things that can diminish the engine's power, like valves that aren't big enough, a restrictive exhaust system, problems with resistance on the intake side, etc. But the displacement is the starting point for the maximum power calculation.

If you have an engine and you want to make it more powerful, what are your options? You can re-bore the cylinders and put in bigger pistons. You can put in a different crankshaft so the pistons travel a further distance in their bore (the resulting engine is called a stroker). Or you can add a turbocharger or supercharger to stuff more oxygen into the same cylinder space.

More info: How Engines Work

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