The title of the best diesel engine of all time is frequently contested between several legendary powerplants, including the 12-valve Cummins 5.9L inline-six, the Ford 7.3L Power Stroke, and the Duramax 6.6L V8 paired with an Allison transmission. These engines earned iconic status among mechanics and operators due to their exceptional durability, massive torque potential, mechanical resilience, and ability to surpass hundreds of thousands of miles with routine maintenance.