Since the invention of the internal combustion engine, engineers have developed hundreds of different engine designs. Most engines, however, fall into four different categories: inline, V-type, boxer and W-type. In this article, we’ll explain the basic characteristics of each engine along with notable examples of each type of engine.
Inline Engines
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Inline engines, sometimes called straight engines, are the most common types of engines; since 2000, nearly half of all new vehicles sold had an inline engine underneath the hood. In this type of engine, the cylinders are arranged in a straight line above the crankshaft. Most inline engines sport four cylinders, but some engines include six or even eight cylinders.
The straight cylinder configuration reduces the need for balancing components, reducing the mechanical complexity of the engine. Inline engines suffer from relatively small amounts of unwanted vibration at typical engine speeds, and the long stroke of their cylinders gives these engines superior torque. Their mechanical simplicity makes them cheaper and easier to maintain.
However, the mechanical constraints of placing all the cylinders in a row makes these engines increasingly unwieldy as the number of cylinders increases. They tend to be taller and longer than other engines of the same power. Additionally, they require stiff and heavy engine block to support the force of the cylinders. At higher engine speeds, this design can be imbalanced, generating unwanted vibration.
Example Engine: Straight Four
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The straight four is the most popular engine in the world by a large margin. The engine features four cylinders in a line. It offers simplicity, ease of access and greater efficiency; the small number of pistons reduces the number of mechanical components necessary while simultaneously eliminating opportunities for power loss. Turbochargers and superchargers can make these engines quite powerful; some high-end tuner cars can extract over 1,000 horsepower from a well-designed straight four. Notable cars with a straight-four engine include the Honda Civic, the Toyota Corolla and the Ford Fusion.
Second Example Engine: Straight Six
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The straight six finds wide applications in rear-wheel drive vehicles with roomy hoods. Arranging the cylinders in a line eliminates some of the balance problems associated with other six-cylinder arrangements while increasing the displacement of the engine. Straight-six engines also offer fantastic torque, making them a great match for trucks and other work vehicles. Notable vehicles with a straight-six engine include the BMW M4, older Jeep vehicles and some versions of the Dodge Ram.
V-Type Engines
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V-type engines split the cylinders into two even banks around the crankshaft; the angle between the two cylinder banks forms a V-shape, giving these engines their name. V-type engines can be found in a wide variety of sizes, from simple two-cylinder engines to gargantuan 24-cylinder engines.
In general, V-type engines are compact and lightweight, especially when compared to inline engines, and this effect is amplified as engines add more cylinders. When the engine is balanced well, these weight savings can translate into improved efficiency. The small form factor of V-type engines also allows them to fit into a wide variety of vehicles where space is an issue, such as motorcycles.
On the downside, V-type engines can be complicated to manufacture and service. If the cylinders aren’t aligned correctly, the engine can be horribly unbalanced, leading to mechanical stress and vibration without additional mechanisms to correct this imbalance.
Example Engine: V8
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For decades, the V8 engine was synonymous with power, speed and American automobiles; most classic muscle cars used a V8 engine. The V8’s eight cylinders are naturally balanced, reducing the complexity of the engine and allowing the engine to deliver an abundance of smooth power. These engines do go through fuel like a beast, but there’s no substitute for the superior power and performance of a V8. Notable vehicles that feature this engine include the Ford Mustang GT, the Chevrolet Camaro Z/28 and the Dodge Ram.
Flat/Boxer Engine
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Flat engines feature cylinders that are arranged horizontally, with the pistons moving left and right rather than up and down. Boxers are a special type of flat engine that split the cylinders into two even banks around a central crankshaft. Flat engines have been built with anywhere from two to 16 cylinders.
Boxer engines are inherently balanced, reducing the need for expensive and complicated balancers. Their horizontal arrangement gives them a low center of gravity, improving power transmission and handling in vehicles that sport these engines. Power delivery is smooth throughout, and the engines are easier to cool because of their spread-out design; for many years, these engines could get away with simple air-cooling.
However, these engines tend to be rather large, and their spread-out design can make maintenance difficult; cylinder heads are often pushed up against the walls of the engine bay, making a simple task like changing spark plugs a knuckle-bruising job. They are also more expensive to manufacture, and they often don’t fit well into typical engine bays.
Example Engine: Horizontally-opposed/Boxer (Subaru)
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Subaru has been using boxer engines in their vehicles for more than 45 years. The engine’s four cylinders balance each other perfectly and deliver a smooth experience when paired with Subaru’s AWD transmission. The engine’s lower center of gravity has helped these vehicles to deliver a unique driving experience, and the boxer engine has become synonymous with Subaru. Notable vehicles that have used this engine include the Subaru Impreza, the Volkswagen Beetle and the Porsche 911.
VR and W Engines
Much like V-type engines, W-type engines derive their name from the shape of the cylinder banks. W-type engines include three or four separate cylinder banks arranged to form a W or arrow shape. Some W-type engines may include more than one crankshaft. The advantages and disadvantages of W-type engines, although scaled up in comparison to V-type engines, largely mirror their simpler cousins. W-type engines are typically used in high-performance or heavy-duty vehicles.
Volkswagen has pioneered many modern W-type engines through the use of its VR-type engine design. VR engines are V-type engines that package the cylinders at a very narrow angle, spaced close enough that a single cylinder head can cover both banks of cylinders. For their W-type engines, Volkswagen pairs two VR banks together, creating an engine that is sometimes called a double-V engine rather than a W-type engine.
Example Engine: W12
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The W12 engine has seen two major designs: a traditional W-type engine featuring three banks of four cylinders, and Volkswagen’s W12 that combines two VR6 piston banks. This engine offers phenomenal power in a compact package, allowing automakers to pair the powerful engine with an all-wheel drive transmission. Using this engine as a starting point, Volkswagen later developed its notoriously powerful W16 engine. Notable cars that have included the W12 engine include the Bentley Continental GT, the Volkswagen Phaeton, and the Audi A8L W12. Although a few concept cars have used the W16 engine, the only production vehicles to use the W16 engine are the Bugatti Veyron and the upcoming Bugatti Chiron.
There are many different engine styles available for today’s car owner, and each engine type has its own advantages and disadvantages; the perfect engine largely depends on the needs of each vehicle.
What kind of engine does your car have?