Car manufacturers have been back and forth, battling one another to develop the best engine in the world, which, according to the focus of this article, would be the most fuel efficient. In pursuit of producing the best engine out there, manufacturers have worked hard to develop exciting new technologies, which have the sole goal of improving fuel efficiency.
From clever transmissions to ECU reprogramming and electrical assistance, this is how engine technologies have altered the efficiency of everyday cars.
CarBuzz has collected information from a variety of sources in an effort to compile this article, a list of which can be found at the end.
1 Stop-Start Technology
BMW
One of the more obvious ways to waste fuel is sitting with your engine idling at traffic lights. Regardless of whether you have a supercharged LS under the hood, or Ford’s gas-sipping 1.0-liter EcoBoost engine, if it’s running, and you’re sitting still, gas is being wasted, and your fuel economy is suffering because of it.
Research from the American Automobile Association found that stop-start technology resulted in a 5% to 7% improvement in fuel economy.
This is why stop-start technology is now common in pretty much every single new car on the market. According to the RAC, the simple but effective tech cuts the engine out at a standstill, only to kick it right back into life when you dip the clutch to go again. According to the RAC, this improves fuel economy by between 5 and 7%.
2 Cylinder Deactivation
Mecum
Cylinder deactivation is nothing new – does anyone remember the infamous V8-6-4 Cadillac engine from the early 1980s? While that early rendition of the technology was essentially a huge flop, the thought behind it was brilliant, and it’s now widespread in many cars and trucks. The basics of cylinder deactivation is, when cruising, some of the cylinders can be shut off, therefore reducing the amount of fuel being burnt. Ford claims the technology can better fuel economy figures by up to 6% in its EcoBoost engines.
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3 Mild-Hybrid Powertrains
BMW
Key Facts About Mild-Hybrid Powertrains
A wide range of automakers use mild-hybrid setups, such as BMW, Audi, and Dodge Mild-hybrids are popular because they improve economy, reduce running costs, and are usually cheaper than full hybrids 48-volt hybrid systems are the most common kind, although some operate at 12 or 36 volts
The role of a mild-hybrid system is to boost the efficiency of the combustion engine, usually at low speeds, such as when pulling away from a set of lights. This is when a traditional gas engine is most uneconomical, as high revs are needed. The electrical motor takes the strain away from the engine here, and in turn, improves overall fuel economy. However, unlike a plug-in hybrid, the motor and battery of such a system aren’t large enough to support gas-free driving.
4 Turbochargers
Audi
The use of turbochargers has totally transformed the automotive landscape in the last 50 years or so, and while manufacturers no longer adorn sporty models with garish ‘TURBO’ graphics, the technology is now more important than ever before. The efficiency of cars is under a real spotlight at the moment, and so even the outrageously fast and specialist models, like McLarens and Ferraris, are now having to keep a close eye on their emissions.
Turbochargers can help downsized engines improve fuel economy as much as 20 to 40 percent in gas and diesel engines, respectively.
As such, smaller engines are being developed, and whacking turbochargers onto the side of them is the go-to method of churning out the big outputs that customers expect. While it’s difficult to establish just how much a turbo will improve an engine’s efficiency, as it depends hugely on the base engine’s design, renowned turbo manufacturer Garrett suggests that gains of 20% to 40% are entirely possible.
Below, we can see a comparison between a modern BMW 330i and an E46 330i from 20 years ago. Despite the modern 330i being heavier and larger, the effect of turbocharging and a more efficient automatic transmission on horsepower and efficiency is clear.
BMW 3 Series Comparison
Model
2025 330i RWD
2005 330i RWD
Engine
2.0L Turbo I4 Mild Hybrid
3.0L I6
Transmission
8-speed automatic
6-speed automatic
Horsepower
255 hp
225 hp
Gas Mileage (city/highway/combined)
28/35/31 mpg
18/27/21 mpg
5 Continuously Variable Transmissions
Subaru
The continuously variable transmission, or CVT for short, is an ingenious design that transformed the way an automatic transmission works. Instead of comprising multiple gears, a CVT uses just two pulleys which move closer or further away from one another, depending upon how fast or slow the car is going. The pulleys are connected to both the engine, and a driveshaft – a belt connects the two, and that is essentially how a CVT is assembled. The idea here is that a CVT can therefore always provide the perfect gear ratio, which results in improved fuel economy, if the engine is always operating at the optimal speed.
6 Direct Fuel Injection
Kia
Direct injection is the process of injecting gasoline directly into the combustion chamber, skipping steps that were once previously necessary in the combustion cycle. According to Consumer Reports, leading fuel-system experts, Bosch, suggests a 15% improvement in fuel economy when this technology is used.
Bosch says that direct injection can return a 15 percent gain in fuel economy.
While the process is effective, and can also reduce other concerns, such as turbo lag, it adds another complication to the process. On the downside, some direct-injection engines are more prone to carbon deposits building up over time, leading to potentially expensive repairs and/or reduced performance as the miles rack up.
7 Variable Valve Timing
Toyota
Variable valve timing effectively gives an engine multiple personalities. In more technical terms, VVT systems manipulate the timing of an engine by changing when, how far, and for how long the valves open. When the engine needs to prioritize performance, VVT will tweak the timing to support this, and it’ll do the same when cruising too, in order to provide the best possible fuel economy. J.D. Power reports that, when Toyota implemented the technology back in the late 1990s, fuel savings of around 6% were achieved.
8 8-/9-/10-Speed Automatic Transmissions
Porsche
While a CVT provides an essentially endless number of gear ratios, more traditional automatic transmissions are limited to the amount of gears they have. The key to providing increased efficiency through the transmission, then, is by simply adding more speeds to the transmission. More gears mean a higher range of revs for the driver to choose from, and so a more precise selection can be made when accelerating or cruising, which can reduce engine stress and improve fuel economy, if the right gear is chosen.
Roll the calendar back a few years, and most manufacturers were fitting five- or six-speed units to their offerings, but that’s not the norm anymore. In the name of efficiency, manufacturers have developed eight-, nine-, and even ten-speed automatic transmissions, such as in the 2024 Honda Pilot.
9 Dual-Clutch Transmissions
Volkswagen
Initially developed for motorsport use, the dual-clutch transmission, or DCT, was discovered to provide improved fuel economy, when compared to that of a comparable old-school auto’ transmission.
Automatic transmission specialists suggest that the DCT design can improve fuel efficiency by around 6% on average, which explains why so many manufacturers have decided to introduce it widespread within their range, perhaps most notably, Volkswagen.
In addition to providing improved fuel economy, a DCT transmission can change gears in mere milliseconds, and so they continue to be popular with driving enthusiasts.
Related RELATED
A dual-clutch transmission uses two clutches, one of which holds the current gear while the next one is ready to upshift or downshift. They deliver quicker response than a torque converter, but can sometimes feel more jerky. Would you want one in your car?
10 ECU Remapping Software
Torque Cars/YouTube
One way to make a huge difference to your fuel economy is by having a specialist remap the settings on your ECU. This, in basic terms, changes the amount of air and fuel that’s delivered to the engine, which, if mapped to do so, can dramatically improve fuel economy. Remapping specialists ProTune claim that fuel economy figures can be improved by up to 20%, although this will be a distinctively different state of tune to the aforementioned performance remaps. However, remaps can also reduce fuel economy, by increasing the rate at which the engine burns fuel, to provide a bigger bang, and more horsepower.
Sources: Ford, RAC, Garrett Motion, Consumer Reports, J.D. Power, AutoTransRUs