Modern piston engines come in a variety of layouts. These different layouts have allowed automobile manufacturers to design and sell a larger variety of vehicle designs, performance levels, and sizes, due to the flexibility the many designs offer. An inline-four engine can be made to fit into a compact vehicle while a V12 engine can provide a lot of power to a mid-engined sports car.
We will assume all the engines discussed here are four-stroke for the sake of simplicity. Stroke one is intake, two is compression, three is combustion, and the fourth is the exhaust stroke. This design is used by a majority of modern and semi-modern vehicles.
The alternative is a two stroke engine, which has different characteristics, and won't be covered on this article, despite having mostly the same design and parts.
Inline & V-Engines
The two most common internal combustion engine layouts are inline, a single row of pistons, and V, two parallel rows of pistons. A V-engine design is usually favored in engines with a larger number of overall pistons because an inline engine would be quite long, which would be hard to design a car around. Inline engines are often favored in low-cost, minimal cylinder count applications. V-engines are generally appear much more symmetrical (when in a rear-wheel drive configuration) due to intake and exhaust placement. Inline-4 engines appear quite frequently in modern compact cars, often due to the small hood length it allows in a front-engine, front-wheel-drive vehicle.Almost every automobile manufacturer produces some form of this engine.
| Type | Piston Banks | Pistons per Bank | Natural Balance? |
|---|---|---|---|
| V4 | 2 | 2 | No |
| V6 | 2 | 3 | No |
| V8 | 2 | 4 | No |
| V10 | 2 | 5 | No |
| V12 | 2 | 6 | Yes |
| V16 | 2 | 8 | No |
| Inline-2 | 1 | 2 | No |
| Inline-3 | 1 | 3 | No |
| Inline-4 | 1 | 4 | No |
| Inline-5 | 1 | 5 | No |
| Inline-6 | 1 | 6 | Yes |
| Inline-8 | 1 | 8 | No |
W-Engines
W-engines are similar to a V-engine, with an additional parallel row of pistons (for a total of three). W-engines are a relatively new arrival for automotive use, but the general design has been around since the early 1900s. The automotive version of this engine is technically a V-engine with staggered piston positioning, as seen in the accompanying video. The layout is favored for its ability to have a large number of cylinders in a relatively small space, in contrast to inline of V-engines. No manufacturer produces these in large numbers, but Volkswagen and Bugatti are notable producers of them.
Boxer/Flat Engines
The flat engine (often called the Boxer engine) is basically a V-engine that has a 180° bank, so that the two rows of pistons face away from each other. Because of this layout, they generally have good rotational balance and give the vehicle a low center of gravity (when placed low), but are quite wide, making them hard to fit into typical engine compartments. Boxer engines are one of only three cylinder layouts (others being the straight-6 and V12) that have a natural dynamic balance, which means the crankshaft doesn't need additional counterbalances to reduce vibration. This layout was invented by Karl Benz just before the 1900s. Porsche and Subaru are notable producers of these engines.
| Type | Piston Banks | Pistons per Bank | Natural Balance? |
| Flat-2 | 2 | 1 | Yes |
| Flat-4 | 2 | 2 | Yes |
| Flat-6 | 2 | 3 | Yes |
| Flat-8 | 2 | 4 | Yes |
| Flat-10 | 2 | 5 | Yes |
| Flat-12 | 2 | 6 | Yes |
H Engine
There are two designs which are considered "H" engines, both of which have a single block containing two crankshafts. One consists of two rows of pistons which appear similar to two inline engines sitting parallel to each other, sharing a single block. For example, an H6 engine of this layout would appear as two inline-3 engines placed next to each other. The other layout is similar in appearance to two boxer/flat engines, one on top of the other, sharing a single block or two half-blocks that are intended to be joined. This layout has four pistons per section, so that an H8 engine would only have roughly the length of an inline-2 or V4. Typically, these engines have only been used in aircraft and a handful of experimental vehicles.
Other Piston Engines
Diesel engines are produced in most layouts gasoline engines are produced in. The difference is not the piston arrangement, but the compression ratio and lack of spark plugs. Single piston engines rarely appear in automobiles, but are seen often in go-karts and motorcycles. A radial engine, or rotary piston engine (not a Wankel Rotary) is a rare sight in a car; it was mostly used in propeller-driven aircraft.
Piston Engine Features
Almost all engines use a single crankshaft; exceptions to this are quite rare. These engines use intake and exhaust Valves to allow an air/fuel mixture in and exhaust out. The four-stroke version is usually found in modern passenger vehicles, and in this type each cylinder is producing power one fourth of the time.
Engines Without Pistons
Pistons aren't the only means of harnessing energy for transportation. Jet, Wankel Rotary, Hüttlin Kugelmotor, and RKM engines don't have pistons, at least in the traditional sense (in the example of the RKM engine).