9 min read
21 Sep

"What are the most efficient engines in terms of power output to fuel consumption?" “Which engines offer the best power output relative to fuel consumption in terms of efficiency?” “Which engines achieve optimal efficiency when it comes to balancing power output and fuel consumption?” “In the realm of engines, which ones excel in delivering power while maintaining exceptional fuel efficiency?” 

Notice how these four questions are essentially seeking the same answers. We get various forms of this same curiosity a lot these days, and the reason isn’t far-fetched. The rising cost of living is forcing car owners to seek cost-saving measures that leave extra pennies that add up in their pockets. 

We’re all familiar with the term, “True Cost of Ownership (TCO),” as it applies to just about every industry imaginable. The term couldn’t be weightier in the automotive industry, where the risk of spending a lot more resources than is sustainable on a vehicle in the long term is scarily high. A major determinant of TCO is the ongoing fuel cost, whether in liquid, gas, or electric form.

According to the American Automobile Association, the steepest increases in gas prices in America are in Midwestern states, where gas prices increased an average of 18 cents and 25 cents, with Washington and California seeing gas prices rise to an average of $5/gallon. 

“Typically, when gas prices increase, the main culprit is the cost of oil," wrote CBS News. 

With the pump price of fuel around the world spiking significantly in recent years, most notably in Nigeria, where fuel pump prices surged more than 300% within three months, even the most indifferent car owner is finally conscious of the fact that investing in a fuel-efficient vehicle brings the advantage of reducing the TCO on the car throughout the vehicle’s lifetime

In fact, a fuel-efficient engine saves its owner money in more ways than just the reduced trips to the gas station. According to FuelEconomyGov, a car owner could save “as much as $1,000 (or more) in fuel costs each year by choosing the most efficient vehicle that meets your needs.” 

In the world of automotive engineering, the quest for efficiency is an ongoing challenge. One fascinating example of this pursuit is the BMW N57 straight-six diesel engine paired with an 8-speed automatic transmission. This dynamic duo showcases remarkable efficiency at varying speeds, intriguing many engineers and enthusiasts. 

Related Reading: 15 Most Fuel-Efficient V6 Engine Cars 2023 

The BMW N57: Efficiency At Different Speeds

BMW_N57D30A Estonia94 via Wikimedia.

At first glance, the difference in fuel consumption between cruising at 90 km/h (56 mph) on a normal road and zooming along the autobahn at 200 km/h (124 mph) seems puzzling. 

Under normal conditions, the BMW N57 engine consumes 5 liters of fuel per 100 kilometers (47 mpg US), while at autobahn speeds, it drinks 10 liters per 100 kilometers (23.5 mpg US). 

This variation defies common intuition, as air resistance increases exponentially with speed. One might expect a 200% increase in speed to result in a 400% increase in fuel consumption. Instead, the opposite is the case, more or less. However, there's a fascinating explanation behind this phenomenon. 

Load And RPM Dynamics

The key to understanding this efficiency lies in the concept of load and engine RPM. The BMW N57 engine, boasting 240 horsepower, operates optimally under specific conditions. 

At 90 km/h, it only requires 15–20 kW (20–25 hp) to maintain speed, while at 200 km/h, it demands around 100 kW (130 hp). Surprisingly, the gearbox maintains the engine at around 3,000 RPM, which aligns perfectly with the engine's sweet spot. 

Optimal Efficiency At Higher Loads

Here's the crucial insight: diesel engines like the N57 exhibit greater efficiency when subjected to heavier loads, surpassing the efficiency achieved in regular city traffic conditions. 

At loads higher than 50%, the engine operates with peak efficiency, despite having slightly less horsepower available at 3,000 RPM. This efficiency shines through at higher speeds, where most vehicles guzzle 2.5–4 times more fuel compared to their lower-speed counterparts. 

Powerful Engines With A Matching Fuel Efficiency

2012 BMW-7-Series-F02.

Engines that share characteristics and efficiency comparable to the BMW N57 include the Audi 3.0 TDI, Mercedes-Benz OM642, and the Volkswagen 3.0 TDI. These engines demonstrate a balance of power and fuel efficiency similar to the N57. 

Of course, the specific performance and efficiency vary depending on the model and year of production, so it's important to consider these factors when pounding the pavement for something akin to the N57. 

In perspective, the BMW N57 is a 3.0-liter straight-six diesel engine typically producing around 240 horsepower. We’ve already established that it excels in fuel efficiency, particularly at higher speeds and under heavier loads, making it ideal for long-distance cruising. 

The N57 engine gets respect for its smooth power delivery, strong torque, and high-speed capability. When paired with an 8-speed automatic transmission, it offers a balance of performance and efficiency. 

So, where can you find the N57? The N57 engine found its way to different generations of the BMW 3 Series, including the F30 and F31 models. 

You can also find the N57 engine in some versions of the BMW 5 Series, such as the F10 and F11 models. Others include the F01 and F02 BMW 7 Series, the F25 BMW X3, the E71 and F16 BMW X6, and some generations of the BMW X5, such as the E70 and F15. 

Audi 3.0 TDI

audi_v6_tdi_engine-via Motorionline.

Enter the Audi 3.0 TDI. Like the N57, TDI is a 3.0-liter V6 diesel engine, but its power output varies across different models and generations, typically ranging from 200 to 286 horsepower. They demonstrate impressive fuel efficiency, especially on highways, where they can rival the N57. 

The reason is that vehicles tend to maintain relatively constant speeds for extended periods on highways. Diesel engines like the Audi 3.0 TDI can operate at lower RPM (Revolutions per Minute) ranges in such conditions. 

Operating at lower RPM means the engine consumes less fuel to maintain speed compared to higher RPMs, which are common in city driving or during acceleration. Secondly, the Audi 3.0 TDI, like many modern diesel engines, uses advanced transmissions that include overdrive gears. 

Overdrive gears have a higher gear ratio than 1:1, which allows the engine to turn at a lower RPM while the vehicle maintains highway speed. This further reduces fuel consumption as the engine doesn't have to work as hard. 

Note also that vehicles encounter less stop-and-go traffic and more consistent airflow on highways, which benefits diesel engines like the TDI because they can maintain a more consistent load and operating condition. 

When coupled with streamlined vehicle designs, this reduces aerodynamic drag, a major contributor to fuel efficiency at high speeds. 

Other factors responsible for the TDI's improved efficiency on highways include a lean-burn mode that maximizes thermal efficiency, sophisticated engine management systems that optimize fuel injection timing, air-fuel mixture, and exhaust gas recirculation (EGR) based on driving conditions, and higher compression ratios compared to gasoline engines. 

Audi_A7_Sportback_3.0_TDI_quattro_S_tronic Thomas doerfer via Wikimedia.

You can find the Audi 3.0 TDI in versions of the Audi A4, such as the B8 and B9 generations, the Audi A6 models, including the C6 and C7 generations, the C7 generation of the Audi A7, the D3 and D4 Audi A8 flagship sedan, some trim levels of the Q5 SUV, several model years of the larger Audi Q7 SUV, some Audi A5 models, including the coupe and Sportback variants, and the Audi Q8 luxury SUV. 

Related Reading: The Seven Most Powerful 4-Cylinder Engines And The Cars Using Them

Mercedes-Benz OM642

Mercedes-Benz_OM642 TatClarkson via Wikimedia.

The Mercedes-Benz OM642, another 3.0-liter V6 diesel engine, offers power outputs ranging from 201 to 255 horsepower, depending on the specific model. 

Notably, the engine often got paired with transmissions that included overdrive gears. These gears allow the engine to operate at lower RPMs while maintaining highway speeds, reducing fuel consumption. 

It achieves commendable fuel efficiency particularly noticeable during highway driving. The engine uses a common rail direct injection system, an advanced fuel injection technology that precisely controls the timing and amount of fuel injected into the combustion chamber. 

It allows for multiple injections during each combustion cycle, which optimizes the fuel-air mixture for efficiency. Also, many versions of the OM642 engine feature a turbocharger, and we know that turbocharging (also known as forced induction) forces additional air into the combustion chamber. 

Thus, enabling the engine to burn more fuel efficiently, and enhancing power output without a significant increase in fuel consumption. 

Another contributing factor to the Mercedes-Benz OM642's improved efficiency is the optimized airflow thanks to an accompanying VGT (Variable Geometry Turbocharger) in some of the engine variants.

It adjusts the geometry of the turbine vanes to match engine load and speed, providing responsive power when needed and improving efficiency during highway cruising. 

We should also mention that the OM642 engine incorporates low-friction components in its design, such as low-friction piston rings and bearings. This minimizes energy losses due to friction within the engine. 

Additionally, some variants of the OM642 engine incorporate SCR (Selective Catalytic Reduction) technology, which reduces harmful nitrogen oxide (NOx) emissions. This technology allows for efficient combustion and helps meet stringent emission standards without sacrificing fuel efficiency. 

Summarily, the OM642 is renowned for its refined performance, low-end torque, and a balance of power and fuel economy. 

Mercedes-Benz_E-Class_W212_ JamesYoung8167 via Wikimedia.

Mercedes-Benz models powered by the OM642 includes both sedan and wagon variants of the E-Class, such as the W211 and W212 generations, the W221 generation of the S-Class, certain W204 generation of the C-Class models in some markets, the W164 and W166 generations of the M-Class (now the GLE-Class), the X164 and X166 generations of the GL-Class SUVs, specific trim levels and markets of the R-Class crossover, various versions of the Sprinter van, and the Mercedes-Benz Viano and V-Class MPVs. 

Volkswagen 3.0 TDI

2013-Volkswagen-Touareg-TDI-engine via Motor Trend.

Volkswagen's 3.0 TDI engine is available in various power variants, typically ranging from 204 to 272 horsepower. The engines exhibit good fuel efficiency, especially on long journeys. Yes, both the VW TDI and Audi TDI are VW-engineered, which explains their shared components and efficiency. A

s you know, both brands typically share engines, excluding Audi’s V8, I5, and RS models. The VW 3.0 TDI often features a long-stroke design, which allows the engine to produce ample torque at lower RPMs. 

This characteristic is advantageous for highway driving, as it reduces the need for frequent gear changes and maintains fuel efficiency. It also features intercoolers that cool the compressed air before it enters the engine. Since cooler air is denser, the result is improved combustion efficiency and reduced fuel consumption. 

Like the OM642, Audi TDI, and BMW N57 above, Volkswagen’s TDI also featured common rail direct injection, variable geometry turbocharger, engine management system, overdrive gearing, and selective catalytic reduction (in some versions) for emissions control. 

These engines often deliver a strong mid-range torque, ensuring responsive performance while maintaining respectable fuel economy. 

Volkswagen_Phaeton_3.0_TDi_nakhon100 via Wikimedia.

Volkswagen's 3.0 TDI engine came in various Volkswagen Group vehicles, including Volkswagen, Audi, Porsche, and other brands under the Volkswagen umbrella. Some models that commonly featured the 3.0 TDI engine included Volkswagen Touareg, Audi Q7, Audi A6, Audi A7, Audi A8, and Porsche Cayenne. 

Formula 1's Remarkable Efficiency

Ferrari_021_engine_front_Museo_Ferrari via Wikipedia.

While we've explored the efficiency of road car engines, it's also worth venturing into the Formula 1 arena to witness another engineering marvel. 

The current 1.6L Turbocharged F1 engines have taken efficiency to extraordinary levels, thanks to stringent regulations on fuel flow rates. 

Unprecedented Thermal Efficiency

These F1 powerplants are pushing the boundaries of efficiency, with current estimates suggesting they achieve an astonishing 50% thermal efficiency. 

Even as this figure surpasses any road car engine, what's even more remarkable is that they achieve this efficiency using fuel that isn't too dissimilar from premium road gasoline. 

Impressive Power Output

Despite the emphasis on efficiency, these Formula 1 engines don't compromise on power. With power output estimates hovering around 550 kW and a maximum allowed fuel flow rate of 100 kg/hr, they boast a Brake Specific Fuel Consumption (BSFC) of approximately 182 g/kW-hr. 

This figure is truly impressive, especially considering that these engines are designed for one purpose: to go fast. In the realm of Formula 1, where every ounce of performance matters, achieving such efficiency levels is a testament to the relentless pursuit of excellence in engineering. 

These powerhouses are a striking example of how innovation and precision engineering can redefine what's possible in high-performance racing. 

The Unmatched Efficiency of Controlled Clean Diesel

VW_Golf_TDI_Clean_Diesel_WAS_2010_via Wikipedia.

When it comes to propelling vehicles efficiently, it's hard to beat the sheer power of well-controlled clean diesel. This remarkable fuel source harnesses an impressive amount of kinetic energy, making it one of the most efficient options available for transportation. 

Consider this: in just one gallon of diesel fuel, there's enough kinetic energy to propel a 3,000-pound vehicle over a staggering 50 miles. To put it into perspective, that's like driving from one city to another without constant refueling. The only thing that can rival this level of efficiency is a diesel locomotive. 

Diesel locomotives are renowned for their ability to move vast loads efficiently over long distances, thanks to the exceptional energy density of diesel fuel.

In essence, they're the giants of the transportation world and owe their incredible power to the same clean diesel technology obtainable in modern diesel-powered vehicles. So, when you're seeking the optimal combination of power and efficiency for your vehicle, it's hard to argue against the merits of a well-controlled clean diesel engine. 

Its ability to convert fuel into motion is nothing short of impressive. It’s a top choice for those with no wish to sacrifice performance on the altar of sustainability on the road. 

A Remarkable ICE Kit

BMW_X3_(F25)_China Dinkun Chen via Wikimedia.

In conclusion, the combination of the BMW N57 straight-six diesel engine and the 8-speed automatic gearbox is a testament to automotive engineering prowess. 

This partnership achieves exceptional fuel efficiency, particularly at higher speeds or when handling heavier loads, such as towing a large trailer. It's a stellar example of how specific engine characteristics, load management, and RPM optimization can yield outstanding results. 

As engineers and enthusiasts continue to explore the boundaries of efficiency in the automotive world, the BMW N57 engine and the others discussed serve as a shining example of what's possible when science and technology merge to redefine our expectations. It's a reminder that there's always room for innovation, even in traditional internal combustion engines.

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