From four-bangers and flat-6s to V-8s and Wankels, we explain the engine types powering commuters, classics, and supercars.
When first on the hunt for a new or used car, you’ve might have run into numbers and letters referencing the engine type a particular car has. For the uninitiated, those little numbers and letters may not mean much. I-4, V-6, and so forth refer to the number of cylinders and their alignment. Below we’ll go into detail on what these and other configurations are, their strengths and weaknesses, and what makes each uniquely cool.
The cylinders in an inline or “straight” engine are positioned … you guessed it, in a straight line. The most common inline engine (and currently the most commonly used engine design) is the inline-4 or I-4. Inline engines benefit from their simplicity. The single cylinder bank means just one camshaft, fewer valve covers and cylinder heads, and many few parts overall and less complexity. The vertical nature of the design also leaves more room in the engine bay, making components easier to access and work on.
In addition to 4-cylinder verities, there are also 3-cylinder versions (like the 1.0L EcoBoost used in the Ford EcoSport or the GR Yaris’s 286hp turbo-3), 5-cylinder version (as in the Land Rover Defender and Audi RS3), and the famed and fabled straight-6 variety (like the Supra’s 2JZ or the Mercedes-Benz 300SL and it’s M198).
Straight-6 engines have a major benefit over their other, smaller inline engines, and that is balance. By basically pairing two 3-cylinder engines together the resulting 6-cylinder engine is able to equalize the primary and secondary forces (essentially the wobbles you get from moving pistons) that otherwise require counterweighting or other methods to mitigate vibration.
Inline engines do have their detractions. Since they are tall, vertical engine types they tend to have a high center of gravity. In addition to being tall, inline engines, and I-6s in particular, are long (hence the long hoods of many I-6 cars). Since inline engines tend to suffer from vibration, they often require balancing shafts or other countermeasures. And finally, given their shape, inline engines are limited in how much displacement they can have.
V engine types feature two cylinder banks in a V shape sharing the same crankshaft and are most often set at between 60° to 90°. They most often come in V-6 (six-cylinder) and V-8 (eight-cylinder) varieties but there are also V-10s, V-12s, and even sometimes V-16 engines have made their way into production cars, like in the aptly named Cadillac V-16.
The V engine design solves some of the inline engine’s shortcomings. V engines are shorter longitudinally than inline engines and more easily fit in cars’ engine bays, especially front-wheel drive cars. Like inline engines, V engines often require balancing shafts or counterweighting to combat vibration.
The V engine has tow major drawbacks. The first is complexity. By splitting the engine into two cylinder banks, a V engine doubles the number of numerous components like valve covers, camshafts, and cylinder heads to name just a few. All those extra parts mean added complexity and more components that can break down and need fixing. This leads us to the second problem with V engines and that is their blocky shape often takes up more room in the engine bay, making maintenance more challenging.
Like V engines, boxer engine types set their cylinder banks at an angle, but in this case, they’re set at a full 180° from each other. This design is why Boxer engines are also referred to as horizontally opposed or “flat” engines. Technically, there is a difference between a boxer and a flat engine. Flat engines are considered “flat Vs” and their crank pins are shared by two cylinders whereas a traditional boxer engine’s cylinders each get their own crank pins. Boxer engines typically come with either four or six cylinders.
Originally designed by Carl Benz (yes, of Mercedes-Benz) and dubbed the contra engine, a horizontally opposed engine doesn’t need balance shafts or counter-weighted camshafts as they are naturally low vibration. Another benefit of boxer engines are their low profile. Sitting low and flat in the engine bay, boxers have a naturally low center of gravity. This compact shape also makes them ideal for rear engine cars like the VW Beetle and Porsche 911.
But boxer engines have their detractions as well. Chief among them is their flat shape and low position in the engine bay make them challenging to work on, often requiring the engine to be pulled for work to be completed. They are also fairly complex. Like V engines, boxer engines double many components thanks to the dual cylinder banks. Also, boxer engines tend to be loud. Some like their distinctive rumble, others, not so much.
Now things get a little weird. A Wankel rotary engine (designed by Felix Wankel in 1951) doesn’t use a traditional piston-driven construction. Instead, a rotary engine features a triangular rotor that spins a drive shaft. It still uses the same Otto cycle of intake, compression, ignition, and exhaust but the ingenious design achieves them very differently. As a lobe of the rotor passes the intake it creates a vacuum sucking in the air-fuel mixture. From there the lobe continues on, sealing the chamber as it passes the intake and then a spark ignites the air-fuel mix (typically with a pair of spark plugs) the resulting explosion spins the rotor on to the exhaust port and pushing out the exhaust. The Mazda RX-7 and RX-8 are the most well-known rotary engine production cars.
Wankel rotary engines benefit from having fewer moving parts than piston-driven engines, they also rev higher with red lines at 9,000 or more rpm, and they are smaller than other engines. The major downside of these engines is their basic inefficiency. Wankel engines have low compression ratios, fail to burn all their fuel in the combustion cycle, and tend to burn oil as well. But they do sound really cool.
Typically, a W engine type (typically in the form of W-12s or W-16s) is comprised of a pair of VR-6 or VR-8 engines combined and sharing a single crankshaft. VR engines fall between a traditional V design and an inline design and feature a very acute V angle and using just two rather than the typical four camshafts of most V engines. Production cars that have used VR engines (often transversely mounted) include the VW Passat and the VW Jetta.
As you may suspect, W engines are pretty complex. The Bugatti Chiron’s 8.0L W-16 features four turbochargers, 64 valves, weighs 880 lbs., and produces 1,479 horsepower and 1,180lb.-ft. of torque. As for servicing this engine, we’d recommend taking it to the experts.