PACCAR vs Cummins

PACCAR and Cummins are two well-known brands in the heavy-duty trucking industry. PACCAR is a Fortune 500 company that designs, manufactures, and sells commercial vehicles, while Cummins is a global power leader that designs, manufactures, and distributes engines, generator sets, and related components.

Here's what most people don't realize: several of the “PACCAR” engines under the hood are actually Cummins engines wearing a PACCAR badge. The PX-7, PX-8, and PX-9 are built by Cummins on the ISB, ISC, and ISL/L9 platforms — PACCAR only handles the electronic tuning and badging. The only engines PACCAR designs and builds entirely in-house are the MX-11 and MX-13.

Why does this matter? Because when you're sourcing DPF, DOC, or aftertreatment parts for a “PACCAR” truck, you may actually be shopping for Cummins-platform parts — which opens up more supplier options than the badge on the hood suggests.

About PACCAR & Cummins

While PACCAR and Cummins are both well-respected brands in the heavy-duty trucking industry, their engines have some differences. PACCAR engines are designed and manufactured in-house, while Cummins engines are built by a separate company. As a result, PACCAR engines are typically only used in PACCAR trucks, while Cummins engines are used in a variety of different truck brands.

In terms of performance, both engines have their strengths and weaknesses. PACCAR engines are known for their durability and fuel efficiency, while Cummins engines are known for their power and reliability. Ultimately, the decision between these engines will depend on the specific needs and preferences of the truck owner.

Like any complex mechanical system, diesel engines can sometimes experience issues or malfunctions. It is not uncommon for engines to require maintenance or repairs at some point during their lifecycle.

Disclaimer: The specifications listed in this article may vary depending on the specific application and configuration of the engine. It is always best to consult the manufacturer's specifications or the owner's manual for the most accurate and up-to-date information on the engine's capabilities and performance.

Is a PACCAR Engine the Same as a Cummins?

The answer to this question depends on which engine and what year you are talking about. So, the answer is both YES and NO.

As far back as 2001, it has been well known that PACCAR and Cummins had allied with each other. Fleet Owner reported on this on March 1, 2001.

As recently as the summer of 2022, we see further evidence that the alliance between PACCAR and Cummins is going strong; in an August 15, 2022 press release on PACCAR.com, it announced, “PACCAR to Offer Cummins X15N Natural Gas Engine.”

So, while PACCAR does design and manufacture proprietary engine designs like the MX-13 and others that are used in its Kenworth and Peterbilt trucks, it has used many Cummins motors in its trucks over the years.

Quick Comparison Table

PACCAR – A Multinational OEM Manufacturer of Vehicles

PACCAR is a multinational corporation that designs, manufactures, and distributes trucks, buses, and other commercial vehicles under the Kenworth, Peterbilt, and DAF brand names. It is headquartered in Bellevue, Washington, and was founded in 1905 by William Pigott as the Pacific Car and Foundry Company.

PACCAR is a global leader in the design and manufacture of heavy-duty trucks, medium-duty trucks, and severe-service vehicles. The company's trucks are known for their fuel efficiency, durability, and advanced technology, and are used in a variety of applications, including long-haul trucking, construction, and other commercial uses.

In addition to its truck manufacturing operations, PACCAR engines and parts are also produced for its vehicles, as well as for other truck manufacturers. The company has a network of dealers and service centers around the world and also provides financing and leasing options for its customers.

PACCAR is a publicly traded company and is listed on the NASDAQ stock exchange. It has a strong financial performance, with a long history of profitability and steady growth. The company has also been recognized for its sustainability efforts, including its use of renewable energy and its commitment to reducing greenhouse gas emissions.

Here is a list of some of the engines that PACCAR offers:

• MX-11: A 10.8-liter inline six-cylinder diesel engine designed and manufactured by PACCAR for heavy-duty trucks and vocational applications.
• MX-13: A 12.9-liter inline six-cylinder diesel engine designed and manufactured by PACCAR for heavy-duty trucks.
• PX-7 (Cummins-built): A 6.7-liter inline six-cylinder diesel engine manufactured by Cummins for PACCAR (based on the Cummins ISB/B6.7 platform).
• PX-8 (Cummins-built, legacy): An 8.3-liter inline six-cylinder diesel engine manufactured by Cummins for PACCAR (based on the Cummins ISC platform).
• PX-9 (Cummins-built): An 8.9-liter inline six-cylinder diesel engine manufactured by Cummins for PACCAR (based on the Cummins ISL/L9 platform).

(Note: PACCAR's PX series engines are built directly by Cummins and re-badged with custom electronic tuning for Kenworth and Peterbilt trucks. Engine tags on PX-series motors will explicitly show they are manufactured by Cummins.)

PACCAR also offers a range of hybrid and electric powertrain systems for its trucks and buses. These include the Kenworth T680E electric truck and the Peterbilt 579EV electric truck.

Cummins – A Global Leader in Diesel & Electric Engines

Cummins engines are built for a wide range of applications, including heavy-duty trucks, buses, recreational vehicles, construction and agriculture equipment, power generation, and marine vessels. Cummins is a global power leader that designs, manufactures, and distributes engines, generator sets, and related components. The company has a reputation for producing high-quality products that are known for their power, reliability, and fuel efficiency.

Cummins engines are available in various sizes and configurations, including inline-four, inline-six, V6, V8, and V12 options. They are used in a variety of different vehicle brands, including Freightliner, Volvo, Peterbilt, Kenworth, and many others. In addition to powering vehicles, Cummins engines are also used in power generation systems, providing electricity to homes, businesses, and other facilities.

Overall, Cummins engines are built to provide reliable and efficient power for a wide range of applications. Whether it's powering a heavy-duty truck across long distances or providing electricity to a remote village, these engines are designed to meet the needs of a diverse set of customers.

Here is a list of some of the engines that Cummins offers:

• B Series: A range of inline four- to six-cylinder diesel engines used in light-duty trucks, buses, and other commercial vehicles.
• ISB / B6.7: A 6.7-liter inline six-cylinder diesel engine used in medium-duty trucks, buses, and vocational vehicles.
• ISC: An 8.3-liter inline six-cylinder diesel engine used in medium-duty trucks and buses.
• ISL / L9: An 8.9-liter inline six-cylinder diesel engine used in heavy-duty and medium-duty trucks and buses (a stroked version of the 8.3L ISC engine platform).
• ISM: A 10.8-liter inline six-cylinder diesel engine used in heavy-duty trucks and buses.
• ISX: A 15-liter inline six-cylinder diesel engine used in heavy-duty trucks and buses.
• L Series: A range of inline four- to six-cylinder diesel engines used in agricultural, construction, and other off-road applications.
• N Series: A range of inline four- to six-cylinder diesel engines used in light-duty trucks, buses, and other commercial vehicles.

Cummins also offers a range of natural gas engines, including the ISX12 G, a 12-liter inline six-cylinder natural gas engine used in heavy-duty trucks, and the B6.7 G, a 6.7-liter inline six-cylinder natural gas engine used in medium-duty trucks and buses.

Cummins ISB engines

The Cummins ISB (Interact System B) is a medium-duty inline 6-cylinder engine designed and manufactured by Cummins. Known for its reliability, fuel efficiency, and low emissions, it serves as the base platform for the PACCAR PX-6 and PX-7 engines.

Key Specifications for the Cummins ISB 6.7 Engine:

• Displacement: 6.7 Liters (359 to 408 cubic inches depending on 5.9L or 6.7L generation)
• Configuration: Inline 6-cylinder
• Bore x Stroke: 4.21 x 4.88 inches (6.7L)
• Compression Ratio: 17.3:1
• Aspiration: Turbocharged and air-to-air intercooled
• Fuel System: Electronic high-pressure common rail
• Maximum Horsepower: 200–325 hp
• Maximum Torque: 520–800 lb-ft
• Emissions Compliance: Meets EPA standards

Is the PACCAR PX-7 a Cummins Engine?

Yes, the PACCAR PX-7 is manufactured by Cummins for PACCAR vehicles and is based on the Cummins B6.7 / ISB platform.

Prior to the 2013 model year, this same Cummins ISB-based platform was badged as the PACCAR PX-6. PX-7 replaced PX-6 to meet 2013 EPA on-board diagnostics requirements, and PX-6 is no longer in production.

A June 26, 2006 press release from PACCAR highlighted the partnership agreement for Cummins to manufacture 6- and 8-liter engine platforms for Peterbilt and Kenworth medium-duty vehicles in North America. These engines are branded as PACCAR engines and tailored specifically for PACCAR chassis, allowing PACCAR to offer proprietary medium-duty power options while sharing proven Cummins architecture.

Key Specifications for the PACCAR PX-7 Engine:

• Displacement: 6.7 Liters (408 cubic inches)
• Configuration: Inline 6-cylinder
• Bore x Stroke: 4.21 x 4.88 inches
• Compression Ratio: 17.3:1
• Aspiration: Turbocharged and air-to-air intercooled
• Fuel System: Electronic high-pressure common rail
• Maximum Horsepower: 200–360 hp
• Maximum Torque: 520–800 lb-ft

Emissions Compliance: Meets EPA standards

Is the PACCAR PX-8 a Cummins Engine?

Yes, the PACCAR PX-8 is a Cummins-built engine based on the 8.3-liter Cummins ISC platform.

Key Specifications for the PACCAR PX-8 Engine:

• Displacement: 8.3 Liters (505 cubic inches)
• Configuration: Inline 6-cylinder
• Bore x Stroke: 4.49 x 5.32 inches
• Compression Ratio: 16.7:1
• Aspiration: Turbocharged and air-to-air intercooled
• Fuel System: Electronic high-pressure common rail
• Maximum Horsepower: 260–350 hp
• Maximum Torque: 660–1,000 lb-ft
• Emissions Compliance: Meets EPA standards

Is the PACCAR PX-9 a Cummins Engine?

Yes. The PACCAR PX-9 is manufactured directly by Cummins for PACCAR and is built on the Cummins ISL / L9 engine platform. Engine tags on a PX-9 explicitly list Cummins as the manufacturer. The PX-9 utilizes the same block structure as the 8.3L Cummins ISC, but with a longer stroke to achieve an 8.9-liter displacement.

Key Specifications for the PACCAR PX-9 Engine:

• Displacement: 8.9 Liters (543 cubic inches)
• Configuration: Inline 6-cylinder
• Bore x Stroke: 4.49 x 5.69 inches
• Compression Ratio: 16.6:1
• Aspiration: Turbocharged and air-to-air intercooled
• Fuel System: Electronic high-pressure common rail
• Maximum Horsepower: 260–450 hp
• Maximum Torque: 860–1,250 lb-ft
• Emissions Compliance: Meets EPA standards

Cummins ISL/L9 Engines

The Cummins ISL (now known as the Cummins L9) is a heavy/medium-duty diesel engine manufactured by Cummins. Because the PACCAR PX-9 is a re-badged Cummins ISL9 platform, both engines share core heavy-duty internal architecture, including wet-sleeve cylinder liners and identical compression ratios.

Key Specifications for the Cummins ISL / L9 Engine:

• Displacement: 8.9 Liters (543 cubic inches)
• Configuration: Inline 6-cylinder
• Bore x Stroke: 4.49 x 5.69 inches
• Compression Ratio: 16.6:1
• Aspiration: Turbocharged and air-to-air intercooled
• Fuel System: Electronic high-pressure common rail
• Maximum Horsepower: 260–380 hp
• Maximum Torque: 860–1,250 lb-ft
• Emissions Compliance: Meets EPA standards

The PACCAR MX Series of Engines

PACCAR MX series engines are a line of heavy-duty diesel engines designed and manufactured in-house by PACCAR for use in Kenworth and Peterbilt commercial vehicles. Built with Compacted Graphite Iron (CGI) heads and blocks, these engines are known for their high strength-to-weight ratio, fuel efficiency, reliability, and long service life.

The primary engines offered in the North American PACCAR MX lineup include:

• MX-11: A 10.8-liter inline six-cylinder engine available in horsepower ratings ranging from 355 to 445 hp and peak torque up to 1,700 lb-ft. It provides an optimal balance of power and weight savings for regional haul, tanker, bulk, and vocational applications.
• MX-13: A 12.9-liter inline six-cylinder engine available in horsepower ratings ranging from 405 to 510 hp and peak torque up to 1,850 lb-ft. It is PACCAR’s flagship engine, engineered for demanding linehaul, over-the-road transport, and heavy-duty vocational hauling.

(Note: PACCAR does not produce an MX-15 engine. For heavy-duty applications requiring a 15-liter engine or up to 605 horsepower, PACCAR equips Kenworth and Peterbilt trucks with the Cummins X15.)

All PACCAR MX series engines feature high-pressure common rail fuel injection and advanced electronic controls to optimize combustion, reduce emissions, and meet strict EPA standards.

The real difference between the MX-11 and MX-13 isn't just displacement — it's the trade-off between weight and torque headroom. The MX-11 is the lighter, more fuel-focused option, ideal when payload capacity matters more than maximum torque. The MX-13 trades some of that weight savings for up to 1,850 lb-ft of torque, making it the pick for linehaul and heavy vocational hauling where you're moving max loads over max distance.

Not sure which one your fleet is running? The engine tag under the hood will tell you exactly which MX you've got — and that's the first thing to check before you order aftertreatment parts.

The Cummins ISX Series of Engines

The Cummins ISX series — including the ISX12, ISX15, and ISX12 G — was Cummins’ heavy-duty engine lineup for trucks, buses, and other heavy-duty vehicles from the late 1990s through 2020. Cummins began phasing out the ISX15 in 2016 in favor of its successor, the X15, with the transition completing by 2020. New Kenworth and Peterbilt trucks are equipped with the X15 today — the ISX/ISX15 name now applies to used trucks, salvage inventory, and legacy parts applications.

At the end of its production run, the ISX12 was available in horsepower ratings from 400 to 600 hp, the ISX15 offered ratings from 400 to 600 hp with up to 2,050 lb-ft of torque, and the ISX12 G — the natural gas variant of the 12-liter platform — was rated from 400 to 500 hp.

Cummins’ current heavy-duty highway engine is the X15, available in Efficiency, Productivity, and Performance series ratings up to 605 hp and 2,050 lb-ft of torque, alongside the X15N natural gas variant introduced in 2024. For parts and service purposes, it’s worth confirming whether a customer’s truck carries an ISX15 or an X15 — the two platforms share a common heritage but use different components in several systems.

All Cummins X-series engines are built with advanced common rail fuel injection systems and electronic controls to improve fuel efficiency and reduce emissions, and are designed to meet current EPA emissions standards.

How to Choose the Right Engine for Your Commercial Truck

Most engine-buying guides tell you to look for horsepower, fuel efficiency, and emissions compliance — as if every badge under the hood represents a totally different piece of engineering. In the PACCAR/Cummins world, that's not quite true, and knowing the difference changes how you shop.

●      Badge vs. build: If your truck runs a PX-7, PX-8, or PX-9, you're driving a Cummins engine under a PACCAR badge — which means Cummins-platform parts, filters, and aftertreatment components are often direct-fit or cross-reference options, even though the engine tag reads “PACCAR.”

●      In-house means a different service network: MX-11 and MX-13 engines are pure PACCAR — designed, built, and supported end-to-end through PACCAR's own dealer network. Parts sourcing and warranty work run through Kenworth/Peterbilt channels only.

●      Match displacement to duty cycle, not marketing: A 6.7L PX-7 and an 8.9L PX-9 aren't just “more power” apart — they're built for different jobs. Medium-duty regional work rarely needs the PX-9's torque, and running an underloaded heavy engine burns more fuel than a right-sized one.

Bottom line: the fastest way to make the right call is to check what's stamped on the engine tag, not just what's printed on the hood. That one detail tells you which parts ecosystem you're actually shopping in.

The Importance of Maintaining Your Diesel Emissions System on Your Commercial Truck

As a commercial truck driver, it's important to maintain your diesel emissions system to ensure that your vehicle is operating at its best. Not only will this help to improve the performance and efficiency of your truck, but it's also important for the environment.

One of the main reasons to maintain your diesel emissions system is to keep your truck running smoothly. The emissions system plays a crucial role in reducing the amount of harmful pollutants that are released into the air, and if it's not functioning properly, it can lead to reduced fuel efficiency and overall performance. By regularly checking and maintaining your emissions system, you can help to ensure that your truck is running at its best and avoid costly repairs down the road.

Another reason to maintain your diesel emissions system is to meet regulatory requirements. Most commercial trucks are required to meet certain emissions standards, and failing to do so can result in fines and other penalties. By regularly checking and maintaining your emissions system, you can help to ensure that your truck meets these standards and avoid any potential issues.

Finally, maintaining your diesel emissions system is important for the environment. Commercial trucks are one of the largest sources of air pollution, and by regularly checking and maintaining your emissions system, you can help to reduce the amount of harmful airborne pollutants. This not only helps to protect the environment, but it also helps to improve air quality for all of us.

In conclusion, maintaining your diesel emissions system is crucial for the performance and efficiency of your commercial truck, as well as for meeting regulatory requirements and protecting the environment. With regular maintenance of your emissions system, you can help to ensure that your truck is running at its best, all while reducing harmful air pollutants.

Don't let a faulty diesel emission system slow you down! Get the high-quality replacement parts you need at DPF Parts Direct. Contact us, and our team of experts can help you find the right parts for your commercial truck and get you back on the road in no time. Trust us to provide you with the best parts at the best prices.

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