Cummins ISL9 400

The number in the name is the output in hp; the suffix EV or H marks calibrations and torque curves. The register lists 31 versions with 260 to 450 hp at 2,100 to 2,200 rpm and 720 to 1,300 lb-ft (976 to 1,763 Nm) of torque between 1,300 and 1,500 rpm; all with electronic direct injection and single-stage turbocharging, certified for model years 2012 to 2016. The service classes recorded are 'MHDD' (medium heavy-duty diesel) and, in four cases, 'Urban Bus' – urban bus certification has its own, stricter test cycles.

The higher rated speed compared with the ISX15 and the broader torque plateau suit duty with frequent starts and automatic transmissions, as is typical for buses and refuse trucks; the engine is regarded as a light six with a good power-to-weight ratio in its class.

On used engines, the condition of particulate filter and SCR system (with many regenerations in city traffic), the variable-geometry turbocharger and the cooling, which in rear-engined buses is often designed to the limit, are what matter.