The Cummins. It’s the engine that brought inline-six architecture, direct injection, the P-pump, and true, industrial-level strength to the ¾-ton truck market. In either 5.9L or 6.7L form, its stroke (4.72-inch, and then 4.88-inch) dwarfs the competition and produces the most usable off-idle torque of any engine in the segment. Higher in the rev range, it’s always been able to hold its own in the horsepower department as well. Not surprisingly, the majority of all aftermarket endeavors are geared toward the ’89-present 5.9L and 6.7L Cummins mills.