Scheinwerfermann / Wikimedia Commons / CC BY 3.0

Is Cummins 12-valve engine the ultimate diesel engine?

Quick notes

  • The Cummins 12-valve diesel engine is considered the ultimate diesel engine.

  • It’s considered the ultimate diesel engine not just for durability and power, but also modifications allowing for greater performance.

  • Modifications allowed the horsepower to be increased from 150 to 1000, which the engine easily handled.

Cummins 12-valve inline-six specs

Dana60Cummins / Wikimedia Commons / CC BY 3.0

The 12-valve Cummins engine is a 5.9L, 1,100-pound diesel workhorse known or being one of the best, if not the best inline-six engine known.

“With a few tweaks, you can take the 12-valve Cummins diesel from 150hp to 1000hp.”

Designed as a commercial, heavy-duty engine, it was introduced as a joint engine between a diesel engine company and Case Co., builder of construction equipment, and tractors. This engine was built to be a beast from the very beginning.

Initially, there were three models of the 5.9L, the 6B, 6BT, and 6BTA. The standard 5.9L was the 6B, the turbocharged version the 6BT, and the turbocharged aftercooled engine being the 6BTA.

The 6BTA was used in pavement rollers, boats, tractors, combines, and similar types of machinery.


It was first introduced into the personal automotive market in 1989 by way of the Dodge Ram pickup truck. Putting the Cummins Turbodiesel into the Ram made it the most potent diesel truck on the market. While only offering 160hp, it provided 400lb-ft of torque with a 4.02-inch bore, 4.72-inch stroke.

“Powerful enough to do all of your grunt work.”

Not only was the Cummins 12-valve engine known aptly as a workhorse, but it was known for durability. Lacking chains and belts, the crank and cam were connected by steel timing gear. The connecting rods and crankshafts were forged, the head and block made of cast iron.

The durability of the 12-valve Cummins is credited to simplicity. The fuel injection system was a mechanical system, which utilized the cam to determine when to inject fuel into the cylinders.

The Cummins 12-valve was utterly mechanical. Once started, it didn’t need any electrical components to keep running.


The reliance on simple mechanics means that the 12-valve Cummins is easily modified for higher performance. This ability stems from the P-Pump.

“The 12-valve Cummins engine is a 5.9L, 1,100 pound diesel workhorse known or being one of the best, if not the best inline-six engine known.”

The first generation 12-valve Cummins used a rotary VE fuel injection pump, but in 194 Cummins introduced the Bosch P7100 mechanical injection pump, which allowed for great tuning.

The set up of the P-Pump allows for easy tuning. Different cut fuel plates can limit the fuel flow at high engine speeds. The lift pump of the P-Pump feeds fuel to the injection pump.

The upward trajectory of the pump’s 6 plungers, which sit in the pump housing on a camshaft. The movement compresses the fuel and moves it through the fuel system into the engine’s cylinders.


“Tuning the engine through the use of modified fuel plates, stiffer governor, and preboos screw tuning adds an extra 150hp.”

If you’re ready to blow the rubber off of your tires, modifications such as block base girdle, head adjustments, new pushrods, and valve springs, larger injectors, larger crankshaft damper, improved lift pump, larger turbos, and alternate intake and exhaust can increase the horsepower to 1000 (which the engine can comfortably handle.

Yes, that needs to be repeated to be properly understood. With a few tweaks, you can take the 12-valve Cummins diesel from 150hp to 1000hp.

The 12-valve Cummins was discontinued in the Dodge Ram in 1998 and replaced with a 24-valve. But it will forever live on in our hearts…and quite a few people’s garages!

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