13 Of The Cummins Heavy-Duty Truck Engines With The Highest Horsepower

With a rich history spanning a century, the Cummins Engine Company was started by self-taught mechanic Clessie Cummins and banker William G. Irwin on February 3, 1919, in Columbus, Indiana. Inspired by Rudolf Diesel's 1897 diesel engine prototype, Cummins produced its first diesel engine, the Model F, in 1924, while its first vehicle, a Cummins Model U-engined Packard, arrived in 1929. Today, Cummins is a large designer and manufacturer of reliable diesel engines.

Some of the world's major stadiums turn to Cummins for uninterrupted power supply. The most powerful Cummins engine is the 4,400-horsepower QSK95, used in locomotives and mining haul trucks. Although Cummins faces strong competition from competitors like Caterpillar, Volvo, Deere & Company, and Pacific Car and Foundry Company (PACCAR), it maintains its position among the world's top diesel engine manufacturers.  Cummins is the preferred engine for many heavy-duty trucks, both in the U.S. and Europe, as well as in several other regions.

Cummins has been the engine supplier for the heavy-duty Ram trucks for over 30 years. The 2025 models of the Ram 2500 are equipped with the 6.7L Cummins engine, which is among the most powerful Cummins heavy-duty truck engines to date. In this list, we focus on some of the most powerful Cummins heavy-duty truck engines with the highest horsepower.

Topping the list is the Cummins X15D, which was unveiled in 2025 at the Brisbane Truck Show. This next-generation diesel engine is the highest horsepower and torque-rated Cummins heavy-duty truck engine ever, delivering a staggering 651 hp and a peak torque of 2,300 lb-ft. This high power-to-torque ratio helps the engine reduce its cruising speed, resulting in improved fuel efficiency. The Cummins X15D is designed on the new 15-liter platform, which offers strong performance.

Compared to the previous X15 engine, the new X15D is 225 kg lighter, which is thanks in part to the new iron block, improved piston design, and enhanced fuel delivery system. The X15D claims a 5-12% improvement in fuel efficiency and features advanced intelligent thermal management technology. The reduced weight also helps the engine lower the front axle's tare, ensuring greater maneuverability, a higher payload, better weight distribution, and reduced wear and tear on tires and suspension.

The latest Cummins X15D also comes with the company's Extreme Pressure Injection (XPI) fuel system and enhanced turbocharger that gives faster throttle response. The Cummins X15D also reduces carbon dioxide emissions by complying with Euro VI standards, thanks in part to a turbocharger with a wastegate. This X15D serves as the base for the Cummins HELM platform. Higher Efficiency, Lower Emissions, Multiple Fuels is a Cummins program intended for global deployment in regions including Australia, North America, and Europe.

Aside from delivering great power output, Cummins is also inclined to make its engines environmentally friendly. In this line, the X15 Euro VI Performance Series engine was launched at the IAA Trade Show in Germany in 2016. This engine was tested in Australia for 4 years and was used in a wide range of vehicles. The X15 Euro VI Performance Series engine produces between 525 and 625 horsepower and also follows the strict Euro emission guidelines without requiring exhaust gas recirculation (EGR).

The engine produces a peak torque of 2,050 lb-ft and a peak horsepower of 625 hp at 1,000 rpm. The X15 Euro VI Performance Series also focuses on enhancing fuel efficiency by 6% over previous engines, while minimizing carbon dioxide emissions. This is thanks to Cummins' Extreme Pressure Injection (XPI) system, which also enables better throttle response. The advanced electronic control module reads and analyzes a lot of data at once, ensuring the engine runs smoothly and efficiently. The X15 Euro VI engine is available in two variants: the Performance Series and the Efficiency Series.

Improved Fleetguard fuel and oil filters hold more dirt particles and contaminants, providing better engine protection and making maintenance intervals longer, saving both time and money. You will find the Cummins X15 engine inside trucks made by Freightliner, International, Peterbilt, Volvo, and Kenworth. 

The Cummins X15 Euro VI is the base engine of the X15 series from Cummins. The Performance Series and Efficiency Series are the two different forms of the Cummins X15 Euro VI engine. The Cummins 15-liter engine is designed to meet European emission regulations and was introduced in 2016 at the IAA Trade Show in Germany. The X15 Euro VI retains the best features of the ISX15 engine but comes with increased thermal efficiency, ensuring that more fuel is converted to energy instead of being wasted as heat. High compression ratio helps maximize fuel burn and power output performance.

Although the X15 Euro VI engine emphasizes power, it also focuses on maximizing fuel economy and reducing carbon dioxide emissions. It produces between 410 and 617 horsepower with a peak torque of 2,050 lb-ft at 1,000 rpm. In addition to being a capable Cummins heavy-duty truck engine, the X15 Euro VI also finds applications in long-haul trucks, tankers, fire trucks, and emergency response units. It is designed to meet the demands of high-performance roles that require power, durability, and compatibility.

Smart features such as electronic tools (ADEPT) work effortlessly with automatic gearboxes to improve fuel efficiency by 6%, whereas compact aftertreatment systems enhance service intervals. The upgraded airflow system provides a faster response, and the X15 Euro VI engine is flexible enough to meet global emission standards on highways and off-road.

Cummins developed the Productivity Series engines for multipurpose usage. From running concrete mixers to large dump trucks, its an engine for heavy professional applications. The X15 Productivity Series brings the best of both the Performance and the Efficiency Series, enabling the engine to deliver exceptional power output with impressive fuel economy. Cummins has released several model years of the X15 Productivity Series, including in 2024, 2021, and 2020. Each variant's power output ranges between 430 and 605 horsepower, with a peak torque output of 2,050 lb-ft, making it ideal for vehicles that require more torque at low rpm.

One of the features of the 2024 X15 Productivity Series Cummins heavy-duty truck engine is that it comes with both Rear Engine Power Takeoff (REPTO) and Front Engine Power Takeoff (FEPTO). This enables the engine to be connected to extra equipment, such as hydraulic pumps or generators, from the front or rear. Cummins has also improved the EGR Assist Braking system, delivering best-in-class engine braking (up to 600 braking horsepower).

The X15 Productivity Series comes with features such as a VGT Turbocharger for better boost at low speeds, an XPI Fuel System for a quiet ride and improved fuel efficiency, a Single-Module Aftertreatment System for reduced maintenance costs, and an advanced electronic module for improved performance.

Although outdated for operations in the U.S. and European countries, the Cummins heavy-duty truck engine, the X15 Euro III, is widely used in other parts of the world, including Asia, Africa, and other developing markets. The Cummins X15 Euro III delivers output between 500 and 600 horsepower and produces a peak torque of 2050 lb-ft. The X15 Euro III shares the same platform as the much newer X15 Euro VI (including the same blocks and pistons), but it doesn't feature the SCR (Selective Catalytic Reduction) aftertreatment system as the Euro VI, which is required to meet the new emission standards.

Instead of going with complex aftertreatment systems, the X15 Euro III opts for fewer components, providing mechanical simplicity and easy maintenance. The missing aftertreatment system also allows this engine to be used in older trucks and can only be installed on pre-2008 registered heavy-duty trucks with ADR80/00 compliance. Thanks to the common rail XPI fuel system and ADEPT technology, it delivers smooth performance, even with an automated manual transmission, for improved fuel economy.

The X15 Euro III is versatile, as it can directly fit into trucks that previously used ISX or Signature series engines, making it an ideal repower option. This engine can be used in a wide range of on- and off-road trucks, where engine emissions rules are a bit relaxed.

The Cummins X15 Euro V was launched back in 2016 as a replacement for the 15-liter ISXe5. This engine is positioned between the X15 Euro III and the X15 Euro VI, ensuring that heavy-duty trucks are emissions-friendly without fully adopting the latest norms. It was designed in such a way that it exceeded the U.S. Environmental Protection Agency (EPA) 2017 greenhouse gas (GHG) and other fuel efficiency standards, making it an ideal offering for both developed and developing markets.

The engine produces power output between 450 and 600 horsepower and a peak torque of 2,050 lb-ft. Its similarity to the ISXe5 engine benefits the X15 Euro V, which is compatible with systems such as the proven Advanced Dynamic Efficient Powertrain Technology (ADEPT) and Connected Diagnosis, as well as the hardware and SCR aftertreatment system that helps reduce emissions and enhance fuel efficiency. Overall, the X15 engine makes sure that you have longer maintenance intervals and a lower cost of ownership.

The X15 Euro V comes with advanced electronic control systems, including SmartCoast and SmartTorque2, which adjust fuel consumption based on driving conditions. It also features a capable braking system, providing over 450 hp of engine braking at 1,500 rpm and a possible 600 hp of engine braking at 2,100 rpm.

Cummins defines its ISX15 engine as the one that offers "exceptional fuel economy, proven reliability, the broadest power range, big bore performance, and high resale value." The ISX15 is widely popular and is used by major Class 8 heavy-duty truck OEMs across North America. The six-cylinder engine, launched in 2013, delivers a power output between 400 and 600 horsepower and a peak torque of 2,050 lb-ft. It can be used inside a heavy-duty truck, long-haul operating machine, fire and emergency response unit, or motorhome.

This Cummins heavy-duty truck engine is equipped with the VGT Turbocharger and XPI Fuel System for the best performance and fuel economy. The Diesel Particulate Filter (DPF) and (Selective Catalytic Reduction) (SCR) ensure that it produces power with improved emissions. In fact, the ISX15 was the first engine to meet 2014 Environmental Protection Agency (EPA) and Department of Transportation (DOT) regulations, a year ahead of schedule.

Almost all Cummins engines are designed to lower operating costs, and the ISX15 is no exception. It is extensively used by Peterbilt, Kenworth, LoneStar, and Western Star trucks. The reliability, economy, and durability on offer make the ISX15 a suitable choice for major American truck OEMs.

The Cummins ISX15 is a six-cylinder, 15-liter diesel engine that has been a cornerstone in the trucking and commercial vehicle industries since its introduction in 1990. The 2010 version is no different. The ISX15 got the Selective Catalytic Reduction (SCR) technology, which not only lowered the emissions but also helped with better fuel economy. It produces an output of between 400 and 600 horsepower with a peak torque of 2,050 lb-ft.

The ISX15 EPA 2010 is available for heavy-duty trucks, motorhomes, and long-haul vehicles in North America, Africa, the Middle East, Asia Pacific, and Europe. Cummins added improved filters, a cooled EGR system, and its proprietary VGT Turbocharger to the aftertreatment system, which allows the engine to remain emission-free and meet the 2010 standards.

The ISX15 EPA 2010 also came with a fully integrated electronic system that delivered optimal performance and reduced fuel wastage by controlling everything from how the air enters the engine to how exhaust gases are treated.

To meet the EPA (Environmental Protection Agency) 2007 emission standards, Cummins launched the ISX EPA 07 compliance engine. This heavy-duty truck engine produces power output between 385 and 600 horsepower and a peak torque of 2,050 lb-ft. It was fitted with a cooled EGR system, Cummins' proprietary VGT Turbocharger, upgraded fuel injection, and particulate filter, ensuring smooth performance while lowering fuel consumption and operation costs.

Thanks to the dual overhead camshafts, one camshaft controls the fuel injection, while the other handles air intake and engine braking, resulting in a powerful engine output. A truck equipped with a Cummins ISX EPA 07 engine can slow heavy loads without relying on the brakes, thanks to the 600 hp of braking force. The engine features a single control module that manages the engine, emission system, and other components for improved overall performance.

The mid-stop cylinder liners give the engine flexibility to handle different coolant types without damaging the internals. Many major truck companies, such as Freightliner, Kenworth, and International ProStar+, use the ISX EPA 2007 in Class 8 truck fleets.

Cummins introduced the X15 Euro VI-compliant engines to strengthen its reputation as a maker known for engines with the longest service intervals. In the X15 series, which includes the Performance Series, Productivity Series, and Efficiency Series, the Efficiency Series is the one that prioritizes fuel economy over performance. However, that doesn't mean it's low on performance numbers.

The X15 Euro VI Efficiency Series engine has a power range between 550 and 580 horsepower with a peak torque of 2,050 lb-ft. It has features such as Hill Climb Assist, which offers access to more power for smooth maneuverability on hills. Cummins says that the X15 Euro VI Efficiency Series is for the linehaul operators who want the best fuel economy. Notably, it is 5% more fuel efficient compared to the Euro 5 X15 engine.

The engine doesn't feature an EGR (Exhaust Gas Recirculation) to meet the Euro VI emission standards, the result of which is the engine being simpler and more reliable. Cummins has used the ADEPT system control feature that ensures better sync with automated manual transmission gearboxes for improved fuel efficiency.

Both the 2021 and 2024 Cummins X15 Performance Series engines deliver between 525 and 565 horsepower. They are designed for drivers who want aggressive throttle response as soon as they put the pedal to the metal, without compromising on reliability. 

The 2021 X15 Performance Series was developed to meet the EPA and Greenhouse Gas Phase 2 requirements. It achieved Cummins' best "Percent Zero Touch" and lowest "Touches Per Thousand" metrics (a measure of introducing very few issues and requiring minimal maintenance) to date, surpassing the 2020 engine. On the other hand, the 2024 variant was compliant with EPA 2024, which has stricter norms. Furthermore, it got an upgraded engine computer for smoother shifting and throttle control. Apart from this, both engines are nearly identical, with some differences in refinements and reliability.

Both the X15 Performance Series engines from 2021 and 2024 are available in Africa, the Middle East, Asia Pacific, Europe, India, Latin America, and North America. It is used in Class 8 trucks from Inland, Kenworth, Freightliner, International, Peterbilt, and Volvo.

Cummins introduced the X15N in 2024, which is the industry's first big-bore natural gas engine. It leverages the Cummins HELM platform's flexibility to be used with different fuel types, including natural gas, diesel, and hydrogen. It has a rating of up to 500 hp with a peak torque output of 1,850 lb-ft and is compliant with EPA and CARB (California Air Resources Board) regulations.

The X15N is designed in such a way that it offers up to 10% fuel economy improvement compared to the ISX12N engine. Its carbon dioxide and nitrogen emission levels are 90% below the current EPA standards, and could be a game changer for fleets in North America, since natural gas is available in abundance. The Cummins X15N drops the VGT Turbocharger in favor of the dual-entry wastegated turbocharger, lowering the complexity during maintenance.

The Cummins X15N also comes with a fully optimized powertrain with the latest transmission and fuel delivery systems as per requirements. This engine is used in Class 8 trucks such as the Kenworth T680, Peterbilt Models 579, 567, and 520, and Freightliner Cascadia.

Setting a benchmark for other engines, the X15 Efficiency Series from Cummins offers the best fuel economy in its class. Each of the X15 Efficiency Series engines from 2020, 2021, and 2024 has a power rating of 400-500 horsepower with a peak torque of 1,850 lb-ft. The engine is tuned to maximize fuel savings and is used in different types of vehicles, such as heavy-duty trucks, dump trucks, cement mixers, fire trucks, or tankers.

It has the same 15-liter X15 engine as the base, similar to the X15 Euro VI Efficiency Series. However, it differs in that this engine is meant for North America and meets the emission standards set by the EPA for 2021 and 2024. On the other hand, the Euro VI variant is designed specifically for Europe, meeting Euro VI regulations.

The 2020 and 2021 X15 Efficiency Series is up to 3.5% more fuel efficient compared to the 2019 variant, depending on specific powertrain configuration. Whereas the 2024 X15 Efficiency Series was 1.5% more fuel efficient compared to the 2020 and 2021 variants.