Cummins X15 Engines — 15L Heavy-Duty Diesel

The X15 Efficiency Series is built for fuel-efficient line haul, typically rated in the 400 to 500 HP range and optimized to work with downsped powertrains and direct-drive transmissions. The Performance Series targets vocational, heavy-haul and demanding over-the-road work, with ratings reaching up to roughly 605 HP and high torque output. Choosing the correct series and rating matters for both performance and emissions compliance.

The X15 powers current-generation Class 8 tractors from the major OEMs, including Kenworth, Peterbilt, Freightliner, International and Western Star, as well as heavy vocational trucks. As the in-production big-bore Cummins, replacement engines are often lower-mileage takeouts from trucks parted out after accidents or driveline changes, alongside professionally remanufactured units.

We dyno-test or verify the condition of used units where possible and source remanufactured X15 engines restored to OEM specification. For a fleet truck you intend to keep, the remanufactured option delivers the longest service life and the strongest warranty.

We supply the X15 as both a long block and a complete drop-in engine. A long block lets you transfer your turbo, fuel system, aftertreatment-related components and accessories to control cost, while a complete engine arrives mostly dressed to reduce shop labor and downtime. Most remanufactured X15 engines are sold on core exchange — we explain the core charge, condition requirements and return process up front so your invoice is clear.