There are actually three different engine configurations commonly used in automobiles:
  • Inline -- the cylinders are arranged in a line in a single bank:


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  • V -- the cylinders are arranged in two banks set at an angle to one another:


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  • Flat (also known as horizontally opposed or a boxer) -- the cylinders are arranged in two banks on opposite sides of the engine:


    Click on image to see animation

You can find, for example, inline 6 cylinder engines, flat 6 cylinder engines and V-6 engines. If you built all three of these six cylinder engines to the exact same specifications -- same displacement, same valves, same intake and exhaust systems, etc. -- they would likely perform nearly identically. Displacement is displacement.

However, there would be a number of differences between the engines in use. Here are several of them to give you a taste:

  • An inline engine is long and narrow. In small cars in particular, a long, narrow engine mounted transversely can allow a very short hood. In an air-cooled engine, the inline configuration is sometimes harder to cool.
  • A flat engine is wide and flat. This gives it a low center of gravity.
  • A V engine is a compromise between the two. It tends to be more cubical in shape.
  • The inline shape needs only half as many camshafts as a V configuration (if using overhead cams), which can lighten things slightly.
  • There can be differences in the amount of metal required in the block, meaning that one type might be lighter than the other.
  • There can also be cost differences during manufacture.
Designers choose among a number of variables when deciding which configuration to use in a car. Variables include cost, space available under the hood, position requirements, existing manufacturing facilities, power to weight ratio, etc.

People sometimes get religious about engine configuration.

Check out these links for more information on engines: