Mythbusted: Is a smaller engine always more fuel efficient?
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A smaller engine always uses less fuel, since its capacity is smaller - while that seems to make perfect sense, it really might not be the case these days.

Category: Car Buying Advice

How do you make a car more fuel efficient? At one point it seemed that a smaller engine is the secret to that. Economy cars such as the famed Kei-class cars from Japan are well known as budget personal car offerings, and these were found with engine capacities ranging from 360cc to 660cc.

Indeed, in earlier days, powerful cars with large engines (think of American muscle cars) were gas guzzlers, while economy-oriented family cars tend to be fitted with smaller engines to achieve an acceptable fuel economy. So does this mean that as long as an engine is smaller, it will always be more fuel efficient? It isn't exactly so, and here are a few reasons why.

Technological improvement has changed things up

Engines with older technology tend to consume more fuel
With the advancement of technology, car drivetrains are getting more efficient and refined. It's pretty normal for a larger engine built with modern technology to be as efficient as smaller engines of the yesteryears.

The improvement in fuel consumption can be associated with engine technology such as fuel injection - introduced as a replacement for mechanically controlled fuel systems that uses carburettors, the precise and controlled fuel injection system allowed a bump in efficiency.

A high-tech engine such as this TSI engine in the Skoda Scala is able to offer an impressive fuel economy
In modern times, much more has been achieved with high-tech systems such as direct fuel injection, cylinder deactivation, start-stop systems and forced-induction.

You can just take a closer look at the Skoda Scala that is equipped with a 1.5-litre TSI engine. This high-tech engine features high-compression, forced-induction, direct fuel injection, cylinder deactivation and start-stop to achieve an impressive official fuel economy of 19.6km/L, all while packing quite a punch.

And it isn't just modern engine tech that has made a difference - the efficiency and features of a modern automatic gearbox also helps to lighten the load on the engine, resulting in improved fuel economy.
A small, low-powered engine can be overworked on a larger sized car

A large, heavy car with a smaller engine can result in subpar real-world fuel consumption
This might sound counter intuitive, but there can be implementations where a smaller engine ends up being even more fuel-thirsty.

Technical data sheets always show that a particular car with a smaller engine variant will have a better fuel economy. But in real world practice, you might end up accelerating and revving the engine harder just to get the car up to speed quickly enough. The situation becomes worse if you are hauling a huge load, or if the car is large and heavy - you'll end up pushing the smaller engine above its most efficient zone.

As a result, it is possible to end up with a car that's not only lacklustre to drive, but also guzzles more fuel than a counterpart with a larger engine.
The aid of hybrid and mild-hybrid technology

Despite being a 7-seater MPV, the Prius+ Hybrid manages 25.6km/L
Hybrid drivetrains combine an electric motor to a conventional engine to assist it in propelling the car.

All internal combustion engines have a specific and rather narrow zone of efficiency within its entire RPM range. An electric motor can aid the engine in the less efficient zones, greatly improving the fuel economy.

Hence, a larger engine with the assistance of a hybrid system can easily achieve the fuel consumption of a smaller conventional engine equipped car.

The 660cc Suzuki Every fails to match the impressive fuel economy of the Prius Plus Hybrid
This can be easily seen from cars such as the Toyota Prius, where the use of hybrid technology allows for some really impressive fuel economy to be achieved.

To put it into numbers, the Toyota Prius+ Hybrid achieves a fuel consumption of 25.6km/L.

Meanwhile the much smaller and lighter Suzuki Every, which has a 660cc engine, only manages 19km/L.

The positive effects of hybrid drivetrains on fuel economy are clear to see.
Performance oriented engines tend to guzzle fuel regardless of capacity

The powerful 2.0-litre engine in the CLA45 S is quite the gas guzzler, even when pitted against engines with a larger capacity
Unlike engines that are destined to go into passenger cars, performance oriented engines tend to use much more fuel in order to produce lots of power - fuel economy clearly takes the backseat in these sporty cars.

It isn't surprising that a smaller-sized performance engine can very well consume much more petrol than a larger engine that was designed with fuel efficiency in mind.

Here's an example - the Mercedes-Benz CLA45 S, which has a 2.0-litre engine and weighs 1,675kg, has a fuel consumption of 10.6km/L. In comparison, the BMW 840i, which is a larger and heavier car weighing in at 1,800kg and has a 3.0-litre engine, has a much better fuel consumption of 13.3km/L.

And in real world usage, the results can be even greater, especially when you account for the manner which performance cars tend to be enjoyed.
In most cases, smaller engines do typically tend to sip on fuel. But with the aid of modern technology, it is no longer always the case. When you are shopping for a car and you find one with a rather large engine, don't just strike it off the list. Take a closer look at the spec sheet, and you might be surprised by how great its fuel consumption is.
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