Cummins X15 engine: displacement, ratings and the trucks that use it

The Cummins X15 is a six-cylinder in-line diesel engine from Cummins Inc. that Cummins’ truck brochures describe as a “big-bore 15-liter engine”. Its marine sheet of April 2020 gives the displacement as 14.9 L [912 in3], and its sheet for fire and emergency vehicles of April 2026, written for the engine that meets the EPA 2027 standards, as 885 cu in and 14.5 L. Cummins’ 2020 truck portfolio divides the truck engine into three series, Efficiency, Productivity and Performance, which together span 400 to 605 hp (298 to 451 kW) and 1,450 to 2,050 lb-ft (1,966 to 2,779 N·m) of peak torque. The documents read name versions for the EPA 2017, EPA 2024 and EPA 2027 standards in North America and for Euro VI elsewhere. On this site five North American truck pages name the X15 in their notes.

Status as of 9 November 2026. Read that day: twelve Cummins documents on the X15 from Cummins’ media library (mart.cummins.com), dated from September 2016 to April 2026: the 2020 truck portfolio and the brochures of its three series, the 2024 Efficiency Series sheet, the quick reference guides for the EPA 2017 and EPA 2024 engines, the sheet for fire and emergency vehicles, the Euro VI bulletin, the off-highway and marine sheets, and the North American truck coverage leaflet for 2021 engines.

Maker, name and layout

Cummins names the engine X15 in all the documents read, and the truck engine by series: “Cummins X15 Efficiency Series”, “Cummins X15 Productivity Series” and “Cummins X15 Performance Series”. Individual ratings carry the advertised horsepower and, on some, a suffix: 400EX or 450ST in the Efficiency Series, X15 605EV or X15 605RV in the Productivity Series. Cummins’ Euro VI bulletin of 2016 places the X15 in its X Series, “first with the ISX15, then the ISX12 and now with a new generation of heavy-duty engines”; Cummins’ braking charts of 2020 set the “2020 X15” beside the “2013 ISX15”. The off-highway version is named X15 as well, and the marine versions X15-M and X15-DM.

The Euro VI bulletin of 2016 says the X Series Euro VI engines share many heavy-duty components with the U.S. Environmental Protection Agency (EPA) versions in North America, including the XPI fuel system and a full-authority single electronic control module, and describes the XPI system’s “Multiple injection events per cycle”. Cummins’ brochures give the engine brake of the truck X15 “up to 600 braking horsepower”; how engine brakes work and what the rules ask of them is covered in retarders and engine braking.

Ratings as Cummins states them

Cummins’ 2020 portfolio gives each series a range in hp and kW, lb-ft and N·m, with its governed speed. The figures below are printed as the documents give them.

In two rows the metric figures as printed do not match the others: in the 2020 portfolio the Performance Series’ 362-451 kW and 2,237-2,279 N·m sit beside 485-565 hp and 1,650-2,050 lb-ft, and the 2024 Efficiency Series sheet prints 2,237-2,779 N·m beside 1,450-1,850 lb-ft. The 2020 Performance Series brochure gives the series as 485-565 hp with 1,650-2,050 lb-ft, and the portfolio says its peak torque starts “at just 1150 rpm”. The Efficiency Series brochure gives “peak torque starting at 950 rpm”. How hp, kW and N·m relate is explained in reading truck power figures.

Efficiency Series ratings

The 2020 Efficiency Series brochure lists eighteen ratings. The EX ratings, it says, “require the use of the X15 Efficiency Series, Endurant transmission and GPS map data” and add features “such as predictive gear shifting, on-ramp boost, predictive engine braking and dynamic power”. The ST ratings are printed with two torque figures each; the brochure does not explain the pair.

Productivity Series ratings

The Productivity Series is, in the portfolio’s words, “designed, built and optimized for vocational, specialty and heavy-haul applications”; it names a quad-axle dump, 130,000 GVW on the interstate and emergency applications among its uses and lists front-end PTO capability. It says ratings from 430 to 500 hp share hardware from the X15 Efficiency Series, “while ratings from 565-605 utilize higher-capacity hardware from the X15 Performance Series.” The Productivity Series brochure of April 2020 lists its ratings by that hardware; it prints 415 kW beside the 505 hp of the X15 505EV and does not spell out the EV and RV suffixes.

Fire and emergency ratings for EPA 2027

Cummins’ sheet for fire and emergency vehicles of April 2026 names the EPA2027 emissions standards for the X15 and says it delivers “up to 605 hp and 2,050 lb-ft of torque”. It gives an idle speed of 600-700 rpm, a governed speed of 2,100 rpm and engine braking of up to 600 hp, and lists four ratings. Fire engines built on truck chassis are covered in fire engines on truck chassis.

Off-highway and marine ratings

The off-highway X15 Performance Series sheet of August 2019 lists twelve ratings from 336 kW (450 hp) to 503 kW (675 hp), all with peak torque at 1,400 rpm, from 2,169 N·m (1,600 lb-ft) up to 2,779 N·m (2,050 lb-ft). The marine sheet of April 2020 lists the X15-M propulsion engine from 336 kW (450 BHP) to 469 kW (630 BHP) and the fixed-speed X15-DM at 373 kW (500 BHP) and 425 kW (570 BHP).

Versions and dates in the documents

None of the documents read gives the year the X15 entered production. The Euro VI bulletin of September 2016 dates the Cummins X Series platform, “first with the ISX15”, back “nearly two decades”, and says the Euro VI X15 and X12 engines “will be certified to Euro VI standards”. The oldest North American truck document read is the quick reference guide for the X15 (EPA 2017). The 2020 Efficiency Series brochure read here is a revision dated 11/24, and the fire and emergency sheet of April 2026 describes the engine for the EPA 2027 standards with a displacement of 14.5 L, where the marine sheet of 2020 gives 14.9 L; the documents do not say whether the EPA 2027 engine is a new design. Among the site’s records, the Freightliner Cascadia page lists the diesel Cummins X15 as available January 2027.

Fuels and emission class

• Diesel. The marine sheet describes the X15 as a “4-stroke diesel”, and the Euro VI bulletin describes the Efficiency Series as running on “diesel fuel”.
• Biodiesel and HVO. None of the documents read mentions biodiesel blends or HVO, the renewable diesel described in what is HVO fuel.
• Natural gas. Three of the site’s model records (Freightliner Cascadia, Kenworth T680, Peterbilt 579) list a natural-gas Cummins X15N, given on the Peterbilt 579 page as 14.5 l, up to 500 hp and 1,850 lb-ft. None of the Cummins documents read for this page describes the X15N, and this page does not cover it.

The North American truck documents are named by their EPA standard: X15 (EPA 2017) and X15 (EPA 2024) in the quick reference guides, and the 2024 Efficiency Series sheet speaks of an engine “compliant with 2024 greenhouse gas standards”. The fire and emergency sheet of April 2026 names the EPA2027 standards and says the engine is “Able to meet the latest emissions standards in all 50 states”. Both quick reference guides say that, in compliance with the EPA and CARB, a diesel exhaust fluid tank that is not refilled triggers an inducement sequence, “limiting engine torque and, eventually, vehicle speed to 5 mph”; what the law requires of SCR systems is covered in SCR and AdBlue.

Outside North America, Cummins’ Euro VI bulletin of 2016 says the Euro VI X15 and X12 engines are designed for markets “from Latin America and China to Russia and Australia as well as Europe and India”, to be certified to Euro VI and the equivalent standards in other regions while able to work where “Euro IV or V standards apply”; the steps of Euro VI and what Euro 7 adds are covered in Euro VI and Euro 7. The off-highway sheet of 2019 says the X15 is “Certified to both EU Stage V and EPA Tier 4 Final emissions standards”, and the marine sheet of 2020 that it “Complies with U.S. EPA Tier 3 and IMO Tier II emissions regulations”.

Trucks and buses on this site with the Cummins X15

No model record on this site lists the Cummins X15 among its engines with kW and Nm figures, so there is no table of recorded kW and Nm figures here. Five North American truck pages name the X15 in their notes, in the maker’s units; the figures are those of each model’s own page and of the source that page cites, not the engine-level tables above.

• The International LT page gives the Cummins X15 as 15 l on the spec cards and 14.9 l in the brochure, 400-565 hp and 1,450-2,050 lb-ft, and in Mexico the Cummins X15 Euro VI at 400-500 hp and 1,550-1,850 lb-ft.
• The Peterbilt 579 page gives the Cummins X15 as 15 l, up to 605 hp and 2,050 lb-ft.
• The Western Star 49X page gives the Cummins X15 at 400-605 hp and 1,450-2,050 lb-ft on the 49X specifications list, and as 14.9 l on the 49X powertrain page.
• The Kenworth T680 page lists the Cummins X15 in Mexico, 400-550 hp, to 1850 lb-ft on the page and 2,050 lb-ft on the 2024 sheet.
• The Freightliner Cascadia page lists the diesel Cummins X15 among the options as available January 2027, and records that Daimler Truck North America’s release of 15 October 2024 gave the Cummins X15 and X15N, due in 2025 and 2026, 400 to 605 hp and 1,450 to 2,050 lb-ft.