Cummins ISB6.7 305

The engine is a direct evolution of Cummins' B-series and was renamed B6.7 around 2018/2019, though the ISB6.7 designation remains common for older model years in the used-parts market. Cummins markets the line as being in its "fourth decade of continuous improvement"; the 2019 version is described as EGR-free and delivers about 5 percent more power and 31 percent more peak torque than the previous model.

The ISB6.7/B6.7 has powered an unusually wide range of vehicles, from the International DuraStar and Kenworth/Peterbilt mid-range trucks to school buses and European DAF LF commercial vehicles.

Like other US highway diesels in this class, the engine meets the strict North American on-highway NOx limit in force since 2010 only with a combination of cooled exhaust-gas recirculation, a diesel particulate filter and an SCR catalyst with AdBlue dosing; injection itself is handled by a high-pressure common-rail system rather than a mechanical inline injection pump. The inline six runs on wet cylinder liners, which can be replaced individually during a major overhaul without swapping the whole block.

On a used example, a complete oil-change and emissions-system service history is the main thing to verify — Cummins itself points to improved service intervals on the current B6.7 generation compared with its predecessor as one of the model's selling points.