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2011 GMC Sierra Denali HD – Click above for high-res image gallery

Say it with us: 397 horsepower and 765 pound-feet of torque. That's what General Motors has been able to extract from its new B20-capable 6.6-liter Duramax V8 diesel engine in the GMC Sierra HD and Chevrolet Silverado HD, which is mated up to a stout Allison 1000 six-speed automatic transmission. For those who like to keep track of these things, which is to say every single person who's actually interested in purchasing one of these earth-moving behemoths, GM's latest Duramax beats out the 2011 Ford Super Duty in the all-important horsepower and torque wars.

That massively powerful powerplant is also more fuel efficient (by 11 percent, though GM isn't quoting actual numbers just yet) and cleaner than the unit it replaces. Each of these benchmarks has something to do with the exhaust aftertreatment systems employed on the Heavy Duty. GM tells us that the new 2011 truck cycles through its DPF filter cleaning process significantly less often than the unit it replaces, which saves a good amount of fuel.

Interestingly, GM representatives also tell us that they had a bit of a back-and-forth with the Feds regarding how best to handle the required refilling of the diesel exhaust fluid tank, which won't run dry until about 5,000 miles. It seems that when the truck gets dangerously low on the exhaust treatment, its speed will be capped at 55 miles per hour. If you run out, the computer nannies will keep you to just a four mph crawl so that you'll never be stranded completely. Want more? Check out our gallery of high-res images below and click here for the rest of the details.





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    • 1 Second Ago
  • 12 Comments
      • 5 Years Ago
      They will be selling chips to defeat the limp mode and the need for urea before the truck is six months old just as they do performance chips for cars.
        • 6 Months Ago
        Yea, I had to buy a cags (computer aided gear selector) eliminator for my Vette when it was new in 01. It over rides the computer that locks you out of second gear at certain rpm's and make you go from 1st gear to 3rd automatically, it locks you out of second most of the time. They were able to get away from the gas guzzler tax by locking you out of second and making only 1 to 3 available unless you lugged it into 2nd or high rpm ed it from 1st into 2nd. First thing I did was buy the cags eliminator bypass, damn computer going to tell me when I can shift my box. The cags eliminator was less than $20.
      • 6 Months Ago
      This is actually a good car, i love it. I would like to know more about it.
      • 5 Years Ago
      I say again for the third time! Nice, a big, powerful, combustion engine with unlimited range (according to average folks) and it has a "limp mode". Ha, haa!

      Damn, I had to post that three times now. Still worth it.
      • 5 Years Ago
      It is true that the Cummins in the dodge does not at the need the SCR since it is efficient enough to pass emission standards.

      You can defeat the urea injection typically by adding resistors to the SCR sensors. That way you can fool the computer into thinking the SCR is receiving an acceptable amount of NOx and that it does not need to inject urea.

      The same could be said for the DPF by simulating the sensors resistance for a signal to not go into regen so you could remove the DPF. Best thing to do if you want to fake out a DPF and not go into regen is to take out the Filter itself and have a hallow section while leaving the sensors. There is only two pressure sensors normally and two temp. sensors. So if the Filter is gone then the pressure sensors will think there is optimal flow in the filter and that no regen is needed. Temp sensors are there to make sure the target regen temps are reached and that there is not some crazy high temps.

      GM might have increased the DPFs ability to heat up to regen temps faster with less fuel by increasing catalyst materials in the DPF.

      But none of this is legal just some knowledge.
      harlanx6
      • 5 Years Ago
      I guess my friends all have 5.9L Cummins engines in their Dodges. They love them and they last forever. Back in the 90s they were getting as much as 20+ MPG (thats what they told me any way. Mileage is like fishing. You don't always know who you can believe.)
      harlanx6
      • 5 Years Ago
      Does Dodge require special exhaust fluid for their Cummins powered heavy duty pickups? If not, the choice would be a no brainer.
        • 6 Months Ago
        @harlanx6
        The cummins does not. However, is does get significantly worse fuel mileage (~13 vs 20+), so in the long run DEF is actually better. It ends up being more cost effective.
        • 6 Months Ago
        @harlanx6
        Yes, the 6.7 Cummins is not a fuel sipper. And the fuel economy difference between the DEF engines and Dodge/Cummins is significant enough that it won't be only a "long run" advantage. It'll pay for itself within a few tanks.
        harlanx6
        • 6 Months Ago
        @harlanx6
        That new Ford Scorpion diesel is impressive.
        harlanx6
        • 6 Months Ago
        @harlanx6
        13 mpg seems low. My friends with Dodges do better.
        • 6 Months Ago
        @harlanx6
        New Dodge trucks with the advanced EGR or older trucks (5.9L/early 6.7L)? The mileage of the new trucks is much worse than the older trucks or new trucks that use DEF.