Even with the recent uptick in popularity of electric vehicles, the vast majority of cars on the road still rely on the tried and true mixture of air, fire, fuel, and compression to give a car power. Simple as it may seem, the way that these four elements are combined can vary quite a bit between different engine types. In addition to cylinder count and induction type (supercharged, turbocharged, or N/A), engines can vary in their cylinder layout.
With some exceptions, there are three distinct ways that an engine can be laid out: inline, flat, and “V.” To help you become more acquainted with what’s under the hood of your car, this article will go into detail on the differences between each of these different engine configurations. Before we do that though, let’s take a crash course on how engines work to get you started: welcome to Engines 101!
How Does an Engine Work?
The first thing to understand about engines is their purpose, which is to generate power to then be transferred to the wheels of the car. They do this by creating thousands of mini-explosions per minute. These mini-explosions move a piston that’s attached to a crankshaft (we’ll be talking about the short-lived rotary style engine a bit later, which works differently). The crankshaft then spins, which creates rotational force. Through a series of gears in your transmission, this force is then sent out to the wheels of the car.
These explosions happen inside something called the combustion chamber, which is the area between the top of the piston and the cylinder head. Within this area you will find the three material ingredients to combustion: air, fuel, and spark (diesel engines do not use spark, but we’ll save that for another article). The fourth important part of combustion is compression, which comes from the pistons up and down, or, as we’ll soon learn, side to side, movement. The air is brought in through the intake system, the fuel through the injectors (at least in modern cars), and the spark comes from the spark plug. These things all come together, go boom, and push the piston in a direction that will spin the crankshaft.
Now that we’ve got Engines 101 out of the way, let’s get into the different engine configurations.
What Are the Different Engine Configurations?
There are three main engine configurations, and then a number of exceptions that we’ll mention briefly, after we get the most popular out of the way. These three most common engine configurations are inline, “V” and flat. These terms refer to the orientation of the cylinders (the sleeves within which the piston moves) in relation to a hypothetical 3D plane that exists within the engine bay.
V style engines
V style engines are one of the most common engine types, and their name should be fairly straightforward in telling the orientation of the cylinders: the cylinders are arranged in a pattern that resembles the letter “V.” V style engines will always have an even number of cylinders, with half of the cylinders occupying each side of the V (at least I don’t know of any exceptions to this rule off the top of my head). For example, a V8 engine will have 4 cylinders on one side of the V, and 4 more opposite them on the other side of the V. The angle at the bottom of the V is most often 90° as well, though there are some exceptions. Within this large family of V style engines, there can be quite a bit of variation with regard to how the engine operates (like pushrod vs. dual overhead cam, or V6 vs. V8), but all V style engines will be structured according to the general principles that we outlined above.
To give an example of a well-known line of V style engines, I will point you toward Chevrolet’s LS line of V8 engines. The LS engine series is one of the most well-known engine groups, for both their robust reliability, as well as potential to be quite powerful in racing applications. They’re simple and effective, and represent V style engines well.
Unlike V style engines, inline or “straight” engines will have all cylinders aligned in a row. Inline engines are typically found in either four- or six-cylinder variants, as an eight-cylinder inline engine would be very long and difficult to effectively package into most cars’ engine bays. Inline engines are known for being smoother and more refined than other engine types, and the inherent mechanical and physical balance of an inline six is difficult to match with other engine types.
A notable example of famous inline engines can be seen in BMW’s N and S series of engines, including the S54, N54, N55, and S55. BMW has been making I6s for longer than I’ve been alive, and they have garnered a reputation for making the best straight sixes in the business over the years, and still to this day. Their I6s are smooth and refined, and are known for making quite an evocative sound when uncorked with an aftermarket exhaust. Another notable example of fantastic inline engines is Toyota’s 2J series of engines, found most famously in the MKIV Toyota Supra. The 2JZ GTE specifically found in the Supra Turbo is known for being highly modifiable without much work being done to the engine internals themselves.
Flat or “boxer” style engines are the final type of engine that we’ll discuss in detail, and they are also the least common of all the engine types we’ve covered so far. Flat engines are arranged in such a way that the cylinders are oriented horizontally, so they oppose each other when firing, as if they are boxing each other (hence the nickname boxer). A simple way to visualize a flat engine is by thinking of it as a V style engine with a 180° angle at the bottom of the V, making it flat.
Flat engines are most notably found in Porsches, as they have been using flat-6 engines exclusively in their famous 911 since the 1960’s. Porsche has had flat engines with varying displacements, states of induction, and cylinder count, but they’ve stuck to their now long-revered configuration for longer than perhaps any other manufacturer has remained exclusive to one engine layout. Another well-known example of a flat engine configuration can be found in the Subaru WRX STi, which uses a Flat 4.
Other Engine Types
The three engine types that are listed above are what you’ll find in 90% of cars on the road. However, there are other engine types making up that last 10%, and some of them are pretty interesting.
VR Style Engines
If an Inline and V style engine could be combined, the result would be the VR engine. The VR engine has no angle, in that all cylinders share the same head, however, they are offset, rather than inline. If you took a V style engine and closed the V like you would if it were an open book, the result would be a VR style engine.
VR engines are almost exclusively used in VWs for reasons that only VW would be able to explain. However, their use in VWs has gained a bit of a cult following as their famous VR6 sounds quite good, and was a potent powerplant in its day.
W Style Engines
In VW’s never-ending pursuit to link every letter of the alphabet to an engine configuration, they came up with the W style engine. The W style engine, which only came in 12-cylinder variants from Volkswagen, is effectively two VR6’s joined at a 90° angle, much like a V style engine. This means you have two banks of 6 cylinders in an offset, VR-style configuration.
The W12 was used in luxury sedans and SUVs and can be found in models like the Audi A8 W12, as well as the Volkswagen Phaeton W12. It is my opinion that the W12 was worth nothing more than a few horsepower and a cool W12 badge, but some will argue that they’re smoother and more well-suited to a luxury sedan than the V8 alternative.
Rotary Style Engines
If you’re interested in a car that will have more hours broken down in your garage than miles travelled, than the rotary engine is for you! The rotary engine is completely different from the other engines that we’ve discussed, as there are no pistons or cylinders. Instead, there is a large, Dorito-shaped rotor than spins within a housing, and creates power using this rotation. Rotary engines are fairly complicated, at least to people who are far more familiar with piston engines, so if you want to learn more about rotaries, I will direct you to the Engineering Explained YouTube channel, which will give a much better explanation than I am capable of.
The rotary engine was most famously used by Mazda in their 90s RX7, which has amassed a following just as loyal as the uber-famous Toyota Supra. This era of tuner cars was made famous by the Fast and Furious movies, but the incredible engines used in these cars, like the 2JZ and the rotary, no doubt have something to do with that fame as well.
As you can see, carmakers like to try lots of different methods to get the same job done: combine air, fuel, and fire to make an explosion and power a car. As for pros and cons, they really aren’t concrete enough to list with confidence, as each style has been executed both very well and very poorly, meaning that any benefits can be attributed to general engineering, not to cylinder configuration explicitly.