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What do engine sizes actually mean?

An engine’s size is otherwise referred to as its ‘capacity’ or ‘displacement’. Without getting too complicated, it’s a measurement of how much space the engine’s pistons operate in. A bigger number means each piston is able to push more air and fuel through the car’s engine every time it moves.

The number is expressed in cubic centimeters (cc) and on engines with a capacity or displacement greater than 1,000cc (one litre) it’s usually rounded up to the nearest tenth of a litre. As a rule of thumb, the bigger this number is, the more power you can expect the engine to produce.

Things have got more complicated recently, though, with the advent of more powerful, smaller-capacity engines. Many of these use technologies such as turbochargers to increase their power. However, if two engines are of the same age, it usually follows that the bigger will be the most powerful.

The amount of power produced by an engine is usually quoted in horsepower. The origin of this measurement is often credited to James Watt, a famous pioneer of the steam engine. He determined a way of expressing how much power a steam engine could produce by measuring it against how many horses are needed to provide the same amount of pulling power.

To confuse things still further, there are various different systems of horsepower measurement, and they aren’t all directly comparable. The most common measurement used in the UK is brake horsepower (bhp).

What does 2.0-litre, or any other number like 2.0, mean?

It’s less common today, but car designations often refer to the engine size as well as the trim level. The bigger the number, the more expensive the car usually is to buy.

If you encounter a number like 2.0, or a phrase like 2.0 litres, this refers to the engine’s capacity. This is the combined capacity of all the engine’s cylinders. Typical modern engines have three, four, six or sometimes eight cylinders – although a few have more or fewer – so a 2.0-litre four-cylinder engine will have a capacity of 500cc in each of its cylinders.

Each piston moves up and down inside its cylinder – the space it moves through is called the combustion chamber. This is where fuel is burnt by the engine to produce power – the explosive force caused by the fuel burning causes the pistons to move. If a car is described as a 2.0-litre, this means the engine’s combustion chambers allow roughly 2,000cc (two litres) of fuel and air to be burnt with every revolution the engine turns.

If this engine is running at 3,000rpm, that means that every piston in the engine can burn 500cc of fuel and air 3,000 times a minute. The more air and fuel an engine can burn, the more power it usually produces.

How does engine size affect performance?

As a larger engine is usually able to burn more fuel and produce more power than a smaller one, a car with a larger, more powerful engine is likely to be able to accelerate faster and tow heavier loads than a car with a smaller engine can manage.

This rule of thumb is less accurate today than in the past. Advances in engine technology mean that some of today’s smaller engines are able to produce more power than certain bigger, more old-fashioned engines.

How does engine size affect fuel economy?

With a larger engine able to burn more fuel with each revolution it turns in a minute (rpm), it’ll usually consume more fuel than a smaller engine would during the same journey.

This is a very important consideration when it comes to choosing a new car. With more powerful, bigger-engined cars usually costing more and using more fuel than those with a smaller engine, it’s worth thinking about how much power you actually need.

If your everyday driving typically doesn’t involve much hard acceleration, carrying of heavy loads or cruising at high speeds, you may find that a smaller, less powerful engine will save you money – not only on fuel but on yearly car tax, which is linked to CO2. A car with higher fuel consumption will usually have higher CO2 emissions, and you can read more about CO2 emissions and fuel economy in our guide.

Small engines tend to be suited to cars that are used predominantly around town. They provide enough performance for short journeys, like trips to the supermarket, school and the office, where high speeds and rapid acceleration aren’t really necessary. As the engine isn’t regularly needed to produce lots of power, it makes sense to keep it small and take advantage of the gains in economy.

If you buy a car with a small engine but try to run it in a way less suited to its strengths, like on long motorway journeys, it will have to work much harder than a larger engine. Not only it will be louder and less refined than an engine suited to motorway cruising, it’ll also be less efficient and is likely to suffer from more wear and tear because it’s under more strain than a larger engine at higher speeds.

There are exceptions, though. More and more engines are using technology such as turbocharging, which can make a small engine behave like a much larger one.

Beyond the size of your car’s engine, your driving style can also contribute to how much fuel you use. Keeping the revs low by changing up to the highest possible gear will help save fuel, as will accelerating and braking gently. Keeping tyres correctly inflated could save you hundreds of pounds each year. Click here for our tips on saving fuel through frugal driving.

You car’s engine size and power will also have an effect on your insurance premium. Cars in low insurance groups (i.e. that are cheap to insure) tend to have smaller, less powerful engines.

What’s the difference between petrol and diesel?

Petrol and diesel are both derived from oil but the way they are produced and the way they are used inside car engines is different, which is why you should never put the wrong fuel in your car. Diesel is more energy rich than petrol per litre and the differences in how diesel engines work make them more efficient than their petrol counterparts.

A diesel engine of the same size as a petrol engine will invariably be more economical. This might make the choice between the two seem straightforward but sadly it isn’t, for several reasons. One is that diesel cars are more expensive, so often you need to be a high-mileage driver in order to see the benefit of the economy versus the higher price. Another related reason is that diesel cars need regular runs on the motorway to stay in good condition, so if you only want a car for town-driving, a diesel may not be suitable. A third reason is that diesels produce more local pollutants like nitrous oxide, which have more of an impact on air quality.

Petrol and diesel engines have different characteristics. Diesel is a good fuel for long-distance, low-rev driving, such as motorway cruising. It also produces lots of power at low engine speeds, making it ideal for towing caravans.

Petrol, on the other hand, is often better for smaller cars and is generally more popular in hatchbacks and superminis. In terms of fuel economy, the choice between a diesel and a petrol engine can be hard – see our ‘petrol or diesel’ guide.

Why would I want a large engine?

Buyers that would benefit from a large engine include caravan owners and people intending to travel long distances on motorways with luggage. Cars with large engines can also be fun for those who enjoy driving, as they’re more powerful and tend to make more noise – an important ingredient for fans of fast cars

Additionally, cars that are large and heavy in their own right tend to require larger engines. Posh 4x4s like the Range Rover (which weighs a couple of tons) require more energy to get moving and mantain speed.

It’s hard to give an absolute rule on what engine size will be sufficient for your specific needs because there are engines of similar sizes that perform significantly differently. However, most engines produced today that are bigger than 1.0-litre should be more than capable of coping with motorway drives.

This article was written by Chris Haining from Car Buyer and was legally licensed through the NewsCred publisher network.


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