Under the hood: A guide to car engine types

Although most of us obsess over the look of a car, very seldom do non-petrolheads pay attention to its most important part – the engine. 

The internal combustion engine comes in various shapes and sizes, each with its own set and advantages and limitations. With this in mind, we have put together a small list explaining all the common engine types so next time you do not have to stand there confused when someone says their car has a "V6" or a "boxer" engine. 

We are going to skip the electric motors for this one, simply because there are only a handful of electric vehicles in Bangladesh and anyone looking to get one likely already knows more than we do.

Inline engines

The most common type of engine used in modern cars, Inline or "straight" engines are types of engines where all the cylinders are placed vertically in line, or one behind another.

Common layout includes 3, 4 or 6 cylinders, while rarer 5, or  8 cylinder setups also exist. Small 3 or 4 cylinder inlines are efficient, relatively simple and cheaper to make, making them automakers preferred choice for compact and fuel-efficient cars. 

However, such designs lack the power generation capabilities of more complex engines, and because of their straight-line design, become less space inefficient as more cylinders are added. 

V engines

To get around the length issue of inline engines, engineers came up with the "V" layout. In such a configuration, an equal number of cylinders are placed parallel to each other, tilted in an angle and connected to a single crankshaft. This resulting shape is largely similar to the English letter "V", hence the namesake.

V6, 8, 10 and 12 cylinder engines are most common, though oddities such as Lancia's V4 does make it to the production line-up once in a while. Compared to inline engines, the V design is much more complicated, but can accommodate double the cylinders at half the space. The additional cylinders can be used to produce more power or run the engine smoother, making them ideal for performance and luxury automobiles.

Because of the sheer number of cylinders, such engines also have large displacement, usually starting from 2,000cc and up making V engine cars a rare sight on Bangladesh roads.

Flat engines

Flat, also known as horizontally opposed and sometimes incorrectly referred to as "boxer" engines (which is a subtype), are engines where the cylinders are laid horizontally flat against each other. A flat engine retains the compactness of a "V" engine but is much shorter in height, resulting in a lower centre of mass. And since the pistons move against each other, they cancel a lot of their own vibration, netting a more smoother running engine. 

On the downside, such engines are much wider. The wide set up helps with the cooling (more metal surface) but makes it hard to fit on most cars. These kinds of engines are also more expensive and complicated to build, making them a somewhat unpopular choice.

However, Subaru is an exception to this however. Their entire vehicle line-up exclusively uses the boxer engine, and is offered only in all-wheel-drive, with the only exception being a two door RWD sports sedan made with Toyota. Another automaker that uses the flat engine is Porsche, whose Boxster nameplate is widely regarded as one of the best sports cars ever made. 

Rotary engine

All the engines on this list use multiple cylinders to drive a single crankshaft, but this one does not, it has none.

Designed by one Felix Wankel, a German with no formal training in mechanical engineering (who also happened to be an enthusiastic member of the Nazi party), the rotary engine uses a triangular rotor (sometimes called a "dorito" because of its shape)  to convert pressure into rotating motion. In a much simpler terms, the walls of the rotor compresses the air against the wall of the engine block, creating the same effect of an engine cylinder in a much smaller space. 

Rotary engines are simpler, smoother, and offer a lot of power for their size. But they are also fuel inefficient, and tend to be more environmentally "dirty" compared to the rest.  

A lot of carmakers tried to work with the rotary engine, but all shelved their designs for one reason or another. Mazda has been the most successful of all the attempts, which for a while, embraced the rotary just like Subaru embraced the boxer. Their rotary swan song is the RX-8 sports car, of which more than a few  can be seen in Bangladesh. 

That being said, Mazda is reportedly working on a new rotary successor to the RX-8, so we might soon witness rotary making a comeback. 

Others 

In addition to these layouts, there are more engine designs out there that are much wilder. There is the "VR" layout, which is basically a V engine made to fit inside an inline engine block. Two of those from a "W" engine the best of such design would be the W16 used exclusively by the multi-million-dollar Bugatti hypercars. There are "X", "H" and U types of engines, but those are mostly used for military and marine vehicles.