Well before the advent of the 21st-century twin-spark Hemi, or "mini big-rig" styling, arguably the single biggest contributor to Chrysler's resurgence in full-size trucks was the introduction of the optional Cummins diesel starting for the 1989 model year. It immediately became a hit with buyers who wanted a durable, capable engine, and with 400 lb-ft of torque when it came out, it was by far the torquiest factory option available.

Today, Chrysler and Cummins are commemorating 25 years of collaboration, and the production of the two-millionth engine for installation in a Ram truck. But this one particular workhorse will live a pampered life as a museum piece that will go on tour around the country.

Since its introduction in 1988 for the 1989 Ram, the B-series inline-six diesel has undergone a number of upgrades and refinements, including a switch to a four-valve design in mid-year 1998, common-rail fuel injection in 2003, and a displacement increase to 6.7 liters in 2007. The highest-output Cummins that will be offered in the 2013 Ram HD will produce 385 hp and 850 lb-ft of torque, more than double the horsepower and torque output of the original 5.9-liter 12-valve engine, which produced just 160 hp and 400 lb-ft.

The Cummins engine continues to be a popular option on the Ram HD, accounting for close to 80 percent of Ram HD truck sales.

Source: Chrysler