No matter which brand you are loyal to, looking back at the company history, and more importantly the engine history, can be a deciding factor in future purchases. Knowing where your favorite brand’s engines came from can help give you a sense of where they might be going, and if purchasing an older engine, what you can expect to experience. Take for instance the Cummins diesel.

Ah, the beloved 12 valve. The first year Dodge offered a 5.9-liter Cummins diesel engine was 1989. These inline six-cylinder engines were direct-injected and turbocharged. Everything about this engine was drastically different than the competition. The Cummins was the only inline six-cylinder offered (still is), and the only direct-injected and turbocharged engine of “the big three.” The 5.9-liter featured two valves per cylinder (i.e. 12 valve) and utilized solid lifters. Between 1989 and 1993, the engine had a Bosch VE44 rotary injection pump. In 1994, the rotary pump was ditched for the infamous inline injection pump, the P7100 P-Pump.

A Holset turbocharger has always been used, and the initial production years didn’t use an intercooler. In late 1991, that changed as an intercooler became standard from that point on. Even with the addition of an intercooler, no horsepower and torque increase was made until 1994 when the P7100 P-Pump was added. Also, 1994 marked the addition of a catalytic converter, and in 1996, the California Air Research Board (CARB) emissions-certified trucks received an Exhaust Gas Recirculation (EGR) valve.

The presence of the P7100 injection pump marks the split horsepower ratings between manual and automatic transmissions.

The 12-valve engines are the easiest to spot due to the individual valve covers. This one belongs to Doug Brarens and resides in his 1939 Chevy Rat Rod.

The Cummins diesel entered the computer age (well kind of) with the 24 valve. This next generation of Cummins to hit the market in 1998 brought quite a few changes with it. The two biggest changes were the addition of the VP44 electronically controlled rotary injection pump and the four-valve-per-cylinder head. While the injection pump was still primarily mechanical, the regulation of the pump was done electronically. Cummins referred to this new engine as an ISB (Interact System B-series), but enthusiasts have always called it the 24 valve.

While most of the engine was actually redesigned, its basic configuration remained the same. There are some issues with this generation of engines. As with Ford and its head gasket problem in the 6.0’s, the 1998 to 2001 24 valves have block-cracking problems. This has been traced to faulty castings at one of the plants. All of the affected blocks have the number 53 embossed on them.

The 24-valve engines did not come with factory compounds. This engine resides in Brandon Carr’s 1972 Buick Riviera.

The third revision of the 5.9-liter Cummins brought about a whole new standard in idle sound quality. The 24-valve engines are arguably the noisiest, and the new common rail engines are arguably the quietest (when they entered the market in 2003). The most notable improvement came from a new fuel system. The VP44 rotary injection pump was replaced with a Bosch CP3 high-pressure fuel pump feeding a single common high-pressure fuel rail. All of the injectors were connected to this fuel rail and saw the same high pressure. The injectors were now electronically controlled, allowing for multiple injection events during each combustion cycle. By using multiple injection events, the noise could be better controlled and regulated (it also helped with emissions).

From a structural standpoint, the engine block was strengthened and a bed plate was added. Most of the rotating assembly remained unchanged. The front timing cover and gear drives were changed to fit the CP3 fuel pump.

This marks the first major redesign of the 5.9-liter Cummins diesel since its introduction in 1989 in the Dodge Ram. The new 6.7-liter engine remained an inline six-cylinder with a bore of 4.21 (up from 4.02) inches and a new, longer stroke of 4.88 inches (up from 4.72). Feeding all of that additional displacement is a Variable Geometry Turbocharger (VGT) which helps create boost down low by changing the internal vanes to increase the pressure of the exhaust gasses contacting the turbine blade. On the big end, the vanes open up, helping to reduce back pressure to support top-end horsepower. The engine meets 2010 emissions, which means that the engine features an Exhaust Gas Recirculation (EGR) cooler, Diesel Particulate Filter (DPF), and catalytic converter.

A huge effort was spent quieting the engine, and the 6.7-liter is actually 50-percent quieter than the previous generation’s 5.9-liter. In addition, for the first time, a factory exhaust brake is optional.