The Cummins diesel engines are popularly known as the Dodge Ram truck's most powerful and efficient engines. They were introduced in the 1989 Ram trucks, and are still being offered as an optional engine for the latest line of Rams. The Cummins diesel engine had two main major development outputs, the 5.9L engine that ran from 1984 to 2006, and the 6.7L engine that was introduced in 2007 and is currently equipped on the latest Dodge trucks.
The 12-valve Cummins 5.9L diesel engine was first conceived in 1984 and was intended for agricultural purposes. It was only in 1989 that it was equipped in a Dodge Ram. It gained immediate popularity because of its ability to be twice as fuel efficient when compared to gasoline engines, and produced nearly twice as much torque when running on low speeds. The 12-valve version ran from 1989 until 1998. Its bore and stroke was 4.02 inches by 4.72 inches, and its compression ratio was 17.0:1. It utilized an Overhead Valvetrain (OHV) with two valves per cylinder, and a solid-lifter camshaft. Throughout its production it had a rated output of 160 to 215 horsepower at 2,500 rpm, and a torque ranging from 400 to 440 lb.-ft. at 1,600 rpm.
In 1998 the 5.9L Cummins had a major upgrade, changing the powertrain from a 12-valve to a 24-valve engine to follow new emission regulations. It utilized a new fuel injection system known as the "Interact System B (ISB)," which used the VP44 rotary injection pump made by Bosch. A high output (HO) was developed for the ISB in 2001, increasing the engine's overall power output. This engine had a bore and stroke of 4.02 inches by 4.72 inches. It had a compression ratio of 16.3:1 for the non-HO version, and had a compression ratio of 17.2:1 for the HO version. It utilized the same OHV configuration with solid-lifter camshaft, but with four valves per cylinder. It generated an output of 235 to 325 horsepower at 2,900 rpm, and a torque of 410 to 610 lb.-ft. at 1,600 rpm.
The 6.7L version is the engine equipped on the latest Rams. This engine was introduced in 2007, and was developed to follow stricter emission regulations. This new engine was equipped with a Variable Geometry Turbocharger, a special diesel particulate filter and an Exhaust Gas Recirculation system. It had a bore and stroke of 4.21 inches by 4.88 inches, and a compression ratio of 17.3:1. It utilized the same OHV configuration as the 24-valve model of the 5.9L engine. Its output was rated at 350 horsepower at 3,013 rpm. Trucks with manual transmission had a torque of 650 lb.-ft. at 1,500 rpm, while automatics generated a torque of 610 lb.-ft. at the same rpm range.
