In an in-line engine, as the name implies, the cylinders are arranged in a row, one behind the other, or horizontally, side by side. With few exceptions, in-line engines are limited to five or fewer cylinders.
Although straight-six cylinder engines have excellent running performance, they make the body very long which restricts their use and excludes entirely installing them transversely with front-wheel drive. For more than six cylinders, construction in the shape of a V has prevailed.
Besides in-line and V-type engines, boxer engines eke out an exotic existence because of their high construction costs.