Detroit Diesel and Cummins built their legacy based on two different approaches to the diesel engine. While Detroit Diesel started with and continued offering two-stroke diesel engines until the start of the 21st century, Cummins has always been known for their four-stroke design. There are pros and cons to each type of engine, which garnered each company to develop loyal followings based on their respective design philosophy.

Detroit's initial Series 71 diesels were two-stroke engines, meaning that the engines completed an entire combustion event into only two piston cycles. Instead of separating intake, compression, power, and exhaust strokes into four piston cycles, two-stroke diesels — like many DD engines until 1998 — combine intake and ignition into a single stroke and compression and exhaust into a stroke. Two-strokes generally have higher power density and weigh significantly less than four-stroke diesels, at the cost of increased emissions and less overall efficiency. Despite Detroit Diesel building their reputation with two-stroke diesels, some of their later four-stroke designs are their most popular models, selling more than a million of their Series 60 four-stroke engines.

In contrast, Cummins has always been famous for their four-stroke diesels. Four-stroke diesel engines have dedicated piston strokes for intake, compression, power, and exhaust processes. While two-stroke engines can generally outperform four-stroke diesels high in the rev range, four-stroke diesels produce better low-end torque, which is better for towing. Four-stroke engines are also more efficient, producing fewer emissions. They also tend to be more reliable, which is a reputation that Cummins has retained since even their earliest Model U and Model K engines. Cummins' four-stroke design helped them take the lead in the on-highway diesel market after the federal government made it harder for two-stroke diesel engines to meet increasingly strict emissions requirements in the mid-2000s.