If you’ve been browsing our comprehensive reviews, you might have come across terms like ‘four-cylinder’, ‘V8’ or ‘straight-six’. You might know it’s something to do with the engine, but what does it mean exactly, and what difference do different ones make? We explain all in this hand guide.
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The science bit
Let’s quickly run through how an engine works. Power is generated when a mix of fuel and air is pumped into an engine’s cylinder. The mix is ignited by a spark, causing a small explosion. This happens across an engine’s numerous cylinders, thousands of times per minute. In each cylinder, a piston moves down as a result of each explosion and that force is sent through the gearbox to the wheels.
Generally, two factors affect how much power an engine produces – the volume displaced by each cylinder – i.e how small or large the engine is – and how many cylinders the engine has. If all other factors remain equal – more numerous and larger cylinders should produce more power, than fewer, smaller ones. It’s these cylinders that are being referred to when terms like V6 are mentioned, but why are there such a variety of names? That’s because the pistons can be arranged in a variety of ways…
An engine’s layout can vary for a number of reasons, often in order to either improve the ease with which the engine fits beneath the bonnet, or to improve its smoothness or even fuel efficiency. Here are the most common configurations…
Inline: All the engine’s cylinders are arranged in a line, facing upwards and usually perpendicular to the car. This configuration is found in the vast majority of family hatchbacks and smaller cars. This term is often used interchangeably with ‘straight’ below.
Straight: Like inline, but the cylinders are positioned in parallel with the car from front to back as opposed to across the engine bay. This layout is frequently used in premium cars, especially BMWs.
Vee: When viewing the engine from the front, the cylinders are arranged in a ‘V’ shape. Each bank of cylinders faces outwards, and drives a common crankshaft at the base of the Vee. This style is generally the reserve of premium and high performance cars because it allows you to squeeze more cylinders into a smaller space compared to inline units.
Flat: Also known as ‘boxer’ or horizontally-opposed engines. The cylinders are laid down on their side in two banks and point away from each other (picture two boxers standing back-to-back and punching outwards). This helps to keep the centre of gravity low, usually to the benefit of handling. Only two car companies currently use flat engines in their ranges – Porsche and Subaru.
VR and W: The VR engine was developed by the Volkswagen Group. It uses a similar principle to V engines but the distance between the two rows of cylinders is so narrow that they’re squished together in one block. A W configuration joins two banks of VR engines together at their base. VR engines are rarely used now, though W engines feature in cars such as the Bentley Mulsanne.
Like the cylinder arrangement, the number of cylinders can be chosen for numerous different reasons, including power, fuel efficiency, and even the noise they make.
Twin cylinder: Only used for very small capacity engines. The only car fitted with this engine currently is the Fiat 500.
Four cylinder: This is the most common arrangement and is almost always fitted in an inline configuration.
Five cylinder: These units are fairly rare and currently only found in a couple of Volvos and the Audi RS3 and RS Q3. They make a distinctive ‘warble’ sound thanks to their odd firing order.
Six cylinder: These engines are frequently used in many premium cars, in both straight and V formations. They make a higher-pitched, racier sound than four- and eight-cylinder engines. Some top-level supercars, including the Ford GT, are using this layout with big turbos to produce the kinds of power that used to require eight or more cylinders.
Eight cylinder and above: V8, V10 and V12 units are used in supercars and luxury saloons. Some top-end Volkswagen-group cars use W12 engines and the Bugatti Veyron used a W16 unit.