Multi-cylinder engines are produced in four common configurations. They are:
- Inline
- "Vee"
- Horizontally Opposed
- Rotary
Inline engines can be found in 2, 3, 4, 5, and 6 cylinder configurations. There have been inline 8 cylinder engines, but they are too long to fit into an engine bay of a conventional modern car.
Cylinders arranged side by side in a single row identify the 'Inline' engine. They can be mounted longitudinally (lengthwise) or transversely (sideways) in the engine bay. However, it is uncommon to find a longer 6-cylinder engine mounted transversely.
"Vee" engines are shorter than an equivalent capacity inline engine. They can be found in 2, 4, 6, 8, 10 and 12 cylinder configurations and consist of two banks of cylinders arranged in a Vee that is joined at the bottom. They are shorter than inline engines, because offsetting the wider top parts of alternate cylinders into the different arms of the Vee allows them to be connected closer together at the crankshaft.
Vee engines can be mounted longitudinally (lengthwise) or transversely (sideways) in the engine bay. A V6 will have two banks of 3 cylinders, a V8 two banks of 4 cylinders.
The angle of the "Vee" varies according to the number of cylinders. The natural angle for a V4 and V8 is 90°. The natural angle for a V6 and V12 is 60° and for a V10 is 72°. Some manufacturers vary their angles due to convenience or design requirements. Some manufacturers use 90° and 15° V6°s
Horizontally opposed engines are commonly found in 2, 4, 6, and 12 cylinder configurations. Like a "Vee" engine, they have two banks, but in this case they are 180° apart. Unlike "Vee" engines their crankshaft differs in the way the pistons are paired. A Horizontally Opposed engine is only fitted longitudinally.
Rotary engines are very powerful for their size, but they do not use conventional pistons that slide back and forth inside a straight cylinder. Instead, a rotary engine uses a rotor which has three convex sides, attached to an eccentric shaft inside a specially shaped housing. As the rotor rotates, it covers and uncovers inlet and exhaust ports, and its curved shape alters the size of the working chambers, which are formed in the spaces between the outside of the rotor and the inside of the housing. For each complete rotation of the rotor, there are three power pulses, and three rotations of the shaft.
A V engine is a common configuration for an internal combustion engine in which the pistons are aligned so that, if viewed along the line of the crankshaft, they appear to be in a V. The V configuration reduces the overall engine length and weight compared to an equivalent straight engine. Various angles of V are used in different engines; depending on the number of cylinders, there may be angles that work better than others for stability. Very narrow angles of V combine some of the advantages of the V engine and the straight engine (primarily in the form of compactness) as well as disadvantages; the concept is an old one pioneered by Lancia, but recently reworked by Volkswagen.
Some V configurations are well-balanced and smooth, while others are less smoothly running than their equivalent straight counterparts. With an optimal angle the V12s and V16s have even firing and perfect balance. The V8s can be balanced with counterweights on the crankshaft. Others, such as the V2, V4, V6 and V10 show increased vibration and generally require balance shafts. In some configurations a special crankshaft is required to achieve even firing.
The way engine cylinders are arranged is called the engine configuration.
Tilting an engine reduces its height. This can reduce the height of the bonnet as well, which allows a more streamlined body shape.
Tilting can be carried to an extreme by lying the engine completely on its side. It is then called a flat engine. This greatly reduces engine height.
As the number of cylinders increases, the length of the block and the crankshaft can become a problem. One way to avoid this is with a V configuration. This design makes the engine block and the crankshaft shorter, and more rigid.
In vehicle applications, the number of cylinders can vary, usually from 4, up to 12.
Common angles between the banks of cylinders are 90 degrees and 60 degrees.
V-type engines are wider than inline engines, and may also be lower.
Horizontally-opposed engines have 2 banks of cylinders, 180 degrees apart, on opposite sides of the crankshaft. A useful design when little vertical space is available. It is shorter than a comparable in-line engine but wider than a V-type.
A rotary engines uses a rotor in a housing, instead of a pistons in a cylinder. This provides a very compact power unit.
