Cummins Vs. PACCAR Engines: How Do They Compare?

You can find various models of Cummins and PACCAR diesel engines in Peterbilt and Kenworth trucks hauling heavy loads across the United States. While most people know about the 6.7L Cummins turbo diesel engine used to power Ram's heavy-duty pickup truck lineup, Cummins engines are also found in a number of medium- and heavy-duty commercial vehicles from dump and box trucks to the tractor portion of 18-wheeled tractor-trailers.

Formerly known as the Pacific Car and Foundry Company, PACCAR engines power more trucks than many realize. PACCAR's Pacific Northwest roots date back to the early 1900s as a manufacturer of train cars used to carry logs for the timber industry. The company now owns Peterbilt and Kenworth, two of the best-known commercial truck brands, for which it builds a variety of diesel engines under the PACCAR banner.

The 12.9-liter MX-13 is the largest diesel PACCAR engine, producing up to 510 horsepower and 1,850 pound-feet of torque. The largest heavy-duty commercial truck Cummins diesel engine, for comparison, is the 15-liter X15. The Cummins X15 Productivity Series diesel engine provides up to 605 horsepower and 2,050 pound-feet of torque.

In addition to the two MX-13 versions from PACCAR, EPA MX-13 and CARB MX-13, the company also offers the 10.8-liter EPA MX-11. The EPA MX-11 weighs 2,200 pounds dry and provides up to 445 horsepower and 1,700 pound-feet of torque. For comparison, the EPA MX-13 weighs 2,500 pounds and the CARB MX-13 tips the scales at 2,750 pounds.

Where heavy-duty commercial trucks are generally of the 18-wheeled semi-truck variety, medium-duty cohorts tend to be box or dump trucks, wreckers, ambulances, or even motorhomes. Medium-duty Peterbilt and Kenworth trucks could have one of two PACCAR diesel engines: PX-7 or PX-9. The 6.7-liter PX-7 provides up to 360 horsepower and 800 pound-feet of torque with a dry weight of 1,150 pounds. The larger 8.9-liter PX-9 weighs 1,695 pounds and generates up to 450 horsepower and 1,250 pound-feet of torque. All of these engines are designed to meet Environmental Protection Agency (EPA) standards.

Cummins provides a couple of other 14.9-liter X15 series diesel engines in addition to the X15 Productivity Series listed above. The Cummins X15 Efficiency Series makes up to 500 horsepower and 1,850 pound-feet of torque and weighs 2,961 pounds dry with the aftertreatment emissions system weighing an additional 191 pounds. While all 2024 Cummins X15 diesel engines are EPA-certified as of 2024 and have the same advertised weight, the X15 Performance Series occupies the middle ground in power output for the three options with up to 565 horsepower and 2,050 pound-feet of torque.

In addition to diesel-powered X15 Cummins options, the company also produces the 2024 X15N, an EPA and CARB compliant natural gas engine with up to 500 horsepower and 1,850 pound-feet of torque. Without the requirement of a diesel engine's DEF components and a lighter weight emissions aftertreatment system, the X15N weighs in at 2,776 pounds total.

Meanwhile, the 2024 Cummins X12 makes up to 500 horsepower and 1,700 pound-feet of torque. Cummins indicates the X12 diesel engine is "designed to give weight-sensitive applications maximum payload." The X12 weighs 2,050 pounds dry and, of course, is also EPA-certified.

Drivers online have differing opinions on whether Cummins or PACCAR diesel engines are best for heavy-duty trucking applications. Some say both are good, while others are loyal to one or the other. Ultimately, the engines are pretty similar and it's a matter of personal choice which one you prefer based on some of the specs we've outlined.

If it helps to make the decision for you, know that PACCAR also provides a two-year 250,000-mile basic warranty and protection for up to five years (or 500,000 miles on major components) for its heavy-duty truck diesel engine lineup. Cummins provides the same base warranty period and offers what it calls "extended coverage" for five years or 500,000 miles.

Cummins claims its X15 diesel engines provide the industry's "most powerful" braking system with up to 600 braking horsepower. Powerful engine braking allows safer truck operation on steep grades by reducing the reliance on mechanical brake systems, which can overheat and fade with prolonged use. Engine braking can also prolong service brake life spans and reduce the frequency of expensive maintenance. While PACCAR diesel engines obviously provide strong levels of engine braking as well, the company doesn't provide any technical details concerning the effectiveness of its engine braking systems.