Diesel Exhaust Tuned Like Fine Instrument

Special Coverage

Diesel Shootout

For decades, powertrain engineers have shed blood, sweat and tears to quiet the inherent clatter of diesel engines, a key consumer complaint that years ago decimated the market for oil burners on this side of the Atlantic.

But is the complete absence of noise a good thing, especially for gargantuan trucks engineered for brute strength and over-the-top manly appeal?

Heavy-duty exhaust engineers at Ford Motor Co., General Motors Co. and Chrysler Group LLC understand this balancing act better than anyone, and for them we are grateful. They provided a symphonic soundtrack for our first-ever Best Engines Diesel Shootout, held in July.

“With the new architecture, we wanted to surprise and delight the customers with new expectations around what a diesel sounds like,” says Adam Gryglak, Ford’s lead diesel engineer. “We thought it should sound like a diesel when it’s working.”

We concur. Although like beauty, the perfect exhaust tone is in the ears of the beholder. And beyond sounding good, the trucks emit nary a poof of smoke, thanks to aggressive aftertreatment and the availability of ultra-low-sulfur diesel fuel.

Of the competitors in the Diesel Shootout – an ’11 Ford F-250 Super Duty, ’11 GMC Sierra HD and ’10 Ram 2500 – judges vary on their exhaust-tone likings.

Aftertreatment makes modern diesel exhaust stream clean as hair drier for Editor Drew Winter.

While some prefer the grunt emitted by the Ram, others find it too noisy. Most like the F-250, which draws praise for its quietness. Judges’ comments on the Sierra range from “shrill exhaust noise” to “very quiet.”

None of the sounds produced by the heavy-duty diesels are coincidental. Rather, engineers gave much thought to the exhaust tuning of each truck in an effort to distinguish it from the pack.

In the case of the Ram, the exhaust is tuned to emit diesel chatter deemed acceptable through customer research.

“We have (the exhaust tone) balanced where you’re still aware it’s a diesel, but it’s not intrusive and annoying,’ says Rod Romain, a Chrysler powertrain engineer who heads HD Ram Diesel Applications. “But it’s not something we’re trying to hide; we’re not ashamed of the diesel.”

The Sierra is engineered to produce different sounds, depending on the output of the engine at any given time.

“You’ll find during city acceleration, you hear engine noise,” says Gary Arvan, chief engineer for GM’s Duramax diesel program. “But when towing on the highway, the engine presence is just not there, which is what that the customer uses it most for.”

As for the F-250, the winner of the Shootout, perhaps Judge Dave Zoia sums it up best. “Quiet, solid and a nice powertrain perception,” he says. “A more baritone idle than Duramax.”

It’s music to our ears.

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