Update from the road: Hands on with the Detroit DD8 engine, Peterbilt Model 579 UltraLoft
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Update from the road: Hands on with the Detroit DD8 engine, Peterbilt Model 579 UltraLoft


Jason Morgan is the content director of Fleet Equipment.

After a slow January, travel picked up for the FE team in February with two major events: the first was a test drive of Detroit’s new DD8, 7.7-liter engine in sunny Palm Beach Florida.

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The DD8 offers the following power ratings:

The DD8 single turbo offering boasts engine ratings of:
• 260 HP, 660 ft./lb.
• 260 HP, 720 ft./lb.
• 280 HP, 800 ft./lb.
• 300 HP, 860 ft./lb.
The dual-stage turbo configuration offers:
• 330 HP, 1,000 ft./lb.
• 350 HP, 1,050 ft./lb.
• 375 HP, 1,050 ft./lb.

and impressive oil drain intervals:

• 55,000 miles for shot haul applications;
• 60,000 miles for long haul applications; and
• 45,000 miles for severe-duty applications.

That’s not to say that you should wait to do your first oil change at forty five thousand miles. The extended drain intervals mean that you have more flexibility in your maintenance scheduling.


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One of the DD8’s most interesting capabilities is its Variable Cam Phasing, a new engine innovation Detroit has introduced to address aftertreatment system headaches that plague vocational fleets. In applications in which long idle time allows the exhaust to cool down to the point where it’s not burning particulate matter off of the DPF, the truck would need to force a regen to get it rolling again. The goal of variable cam phasing is to force the engine heat into the exhaust system more quickly to keep the aftertreatment system temperature up and reduce forced regen situations.


After the test drive, I hopped on a plane and headed across the country to Scottsdale Arizona where Peterbilt unveiled its UltraLoft Model 579 cab configurations. This thing is massive–one configuration sports a spacious single bed, while the other offers a roomy double bunk setup.

Both 80-in. integral sleepers offer massive amounts of headroom, an impressive array of storage—70 cu ft to be precise–large microwave, fridge, a 42-in. hanging height wardrobe, and enough room to fit a 32-in. flat screen TV. Both lower bunks measure in at 85-in. long and 42-in. wide, while the double bunk configuration adds an 82-in. long, 36-in. wide upper bunk.


While that will make drivers happy, the UltraLoft also boasts up to a 2% fuel economy improvement and is 100 pounds lighter when compared to the Model 579 discreet sleeper.

Fleet Equipment Magazine