Cummins has been a leader in the medium duty diesel engine space for decades. There are two main inline-six cylinder turbocharged engine Quality stocks, the 5.9L and the 6.7L with each having multiple variants:

1. 5.9L was introduced in 1984 for agricultural use and 1989 for on-highway vehicles. It was originally offered as a mechanical fuel injection engine with a rotary pump. This version is commonly referred to as the B-Series or “12-Valve”. In 1997 it was updated to an electronical Bosch fuel system with a VP44 high pressure pump and 24 valves. It is known as the ISC (Interact System B). The last version was introduced in 2003 to meet EPA200 requirements with the addition of an EGR (Exhaust Gas Recirculation) cooler and an updated common rail fuel system that utilizes a CP3 high pressure pump. All versions of the 5.9L were painted tan.

2. 6.7L  was originally introduced in 2007 to meet EPA2007 requirements by adding a DOC (Diesel Oxidation Catalyst), DPF (Diesel Particulate Filter) and SCR (Selective Catalytic Reduction). In 2010 Cummins added DEF (Diesel Exhaust Fluid) o comply with EPA2010 requirements, followed by and updated Electronic Control Module (ECM) for EPA2013. Cummins made further advancements on the B6.7 engine to meet EPA requirements for EPA2017, EPA2021 and EPA2027. All versions of the ISB6.7 are painted red.