DaimlerChrysler 5.9L Cummins 600 OHV I-6 turbodiesel

With DaimlerChrysler AG’s “Cummins 600” 5.9L turbodiesel earning a win in this year’s Ward's 10 Best Engines competition, it’s official: in each of the last three years, there’s been an all-new or significantly revised medium-truck diesel engine. Each year, that new diesel won a 10 Best award.

The breakneck pace of diesel development for the hotly contested, astoundingly profitable medium-truck market is the new world order. Sit back for six months to enjoy your position as king of horsepower or prince of torque and your competitors have passed you by. The numbers – and perhaps more important, the refinement – ratchet up that quickly in the medium-duty diesel game.

DaimlerChrysler and engine-development partner Cummins Inc. credit heavy reliance on computer analytical tools for the new Cummins 600’s overnight burst from last in a three-way race (with General Motors Corp.’s Duramax and Ford Motor Co.’s International Truck and Engine Corp.-made Power Stroke V-8 turbodiesels) to front-runner in terms of both power/torque and refinement.

Dennis Hurst, Cummins’ chief engineer for the Cummins 600, says the incredible NVH improvement the 5.9L inline 6-cyl. Cummins 600 displays over the previous-generation engine actually was a tertiary benefit of his team’s pursuit of more power and precise combustion control that makes the engine 50-state emissions-compliant – without the use of expensive and troublesome add-on exhaust-gas recirculation systems rivals employ to reduce the excess oxides of nitrogen (NOx) emissions that plague all diesels.

So in one fell swoop, DC and Cummins went right ahead and tended to both the numbers and the NVH with the heavily revised Cummins 600. The new name reflects the class-leading torque rating of 600 lb.-ft (813 Nm). And the 325-hp rating isn’t sissy stuff, either.

But we challenge even the most-sensitive of posteriors to tell the difference between 550 lb.-ft and 600 lb.-ft. of torque. At those levels, unless the differences are vast, it’s hard to tell (and GM made late-in-the-year revisions to its Duramax that yield closely competitive 590 lb.-ft [800 Nm] and 310-hp ratings).

No, what blew away Ward's judges was the Cummins 600’s almost unbelievable improvements in NVH and refinement. “This engine makes its two competitors seem like garbage-truck engines,” says one tester. “Even when you first start it on a cold morning, the Cummins lights off and settles into idle like a gasoline engine. It’s remarkable.”

Hurst confirms the new Cummins 600’s combustion noise is markedly reduced, and detail changes like a special noise-isolating valve cover and an optimized turbocharger blade design all contribute to noise and vibration reduction. Of course, the inherently balanced I-6 architecture also presents a fundamental advantage over its V-8 competitors.

And the high-tech combustion control (hundreds of thousands of new lines of ECU software code) that makes the Cummins 600 nationally emissions-certified is a huge matter, too. The only aftertreatment system for this engine is a relatively simple oxidation catalyst to control hydrocarbon and particulate emissions.

All we can say is “Wow.” One tester delivered our bottom-line impression regarding the new Cummins 600: “I could drive this truck every day, and I never would have said that before about a medium-duty diesel.”

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