By on September 26, 2016

2017 GMC Sierra Denali 2500HD

A document containing official horsepower and torque numbers for General Motors’ new 6.6-liter V8 Duramax turbo-diesel was found buried on the GM Powertrain website — before the company quickly deleted it

GM’s new 2017 heavy-duty pickup trucks will wade into the nuclear torque war with a whopping 910 lb-ft of twist, with peak torque coming on at just 1,600 rpm. Horsepower is up by nearly 50 to 445 hp at 2,800 rpm — thanks in part to a new turbo design — while the 103 mm bore x 99 mm stroke remains identical.

The L5P’s 910 lb-ft of torque puts it midway between the Ford Super Duty’s 925 lb-ft and the Cummins-powered Ram at 900 lb-ft, however, its 445 hp rating leaves GM with the horsepower crown (versus Ram’s 385 hp and Ford’s 440 hp).

Thew new L5P Duramax is slotted for production at the GM-Isuzu plant in Moraine, Ohio, and will see action in both Heavy Duty Silverado and Sierra twins.

The accidental release comes just days before GM’s new HD trucks are set to officially debut at the 2016 State Fair of Texas, where we should receive transmission and towing specs.

[Image: General Motors]

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50 Comments on “GM Posts (then Deletes) New 6.6-Liter Duramax Turbo Diesel Power Specs...”


  • avatar
    White Shadow

    Great. Now we can pull out those gigantic tree stumps in the yard. Or tow a yacht. Or just carry a load of air around like most truck owners.

    • 0 avatar
      VoGo

      A little early in the day to be waving a red flag in the faces of the B&B bulls.

      • 0 avatar
        White Shadow

        I recently moved from NY down to South Jersey due to a job relocation. It’s certainly nice around here, but everyone and his brother drives a lifted bro truck with oversized mud tires and a loud exhaust system. And they drive them around like the accelerator is an on/off switch.

        It’s actually quite funny to hear how hard the engine is working, but watching how slow the damn things go with those gigantic tires.

    • 0 avatar
      statikboy

      Excellent first post!

    • 0 avatar
      Drzhivago138

      All the horsepower and torque in the world can’t pull out a tree stump if you’ve got no traction. There are these things called tractors that usually do a better job of that.

      No joke, in about 2003 or so I recall my father failing to pull out a 7′ tall lilac with the skid loader or any of his regular 2WD tractors…so he had to use the JD 7020 4WD. Just backing it straight up to the house and driving straight out again tore up the lawn something bad. But that lilac must have had as much root below as it did branches above. The next time we decided a lilac by the house had to go, we just hacked it off below ground level and covered the spot with a rock garden.

  • avatar
    dal20402

    All these increases in boost accomplish is force the driver to shell out for aftermarket gauges so they can figure out how hard they can push without overheating or overstressing the engine.

    If I had one of these, I’d want a tune that had less gaudy numbers but could work at WOT all day long without breaking a sweat. Something like, say, the Class 5-6 applications of the Power Stroke that feature around 275 hp and 600 lb-ft.

    • 0 avatar
      VoGo

      You seem to have forgotten the importance of which logo the imaginary tiger urinates on.

    • 0 avatar
      bumpy ii

      I would expect you could buy a medium-duty tune from a vendor, or simply upload the factory tune.

    • 0 avatar
      stuki

      Just get the Cummins Ram with the Manual. Duh! Always get the manual :) That thing is rated close to the commercial offerings of the engine.

      That being said, the reason the Big3 can keep pushing peak torque and HP figures ever higher, is because engine management is now so well understood, that you can still run at WOT all day. The engine will simply back off to protect itself. For extended limit towing uphill in the heat, the above manual will do just as well as the higher torque/power autos, as the trucks are ultimately cooling limited under a big enough load.

      But since pickups aren’t generally used that way, the ability to use short bursts of acceleration, to get ever more gargantuan 5th wheels (don’t get me started…..) up to something resembling the speed of traffic, in the distance allotted by a freeway on ramp, can make the whole towing experience less nerve wracking for some.

      • 0 avatar
        Drzhivago138

        The Cummins available with the 6-speed is the non-HO version–“only” 350 HP and 660 lb-ft of torque. And what’s wrong with a big fifth wheel, anyway?

        • 0 avatar
          stuki

          He wanted a lower tune, as a safety margin.

          Nothing wrong with big 5ths. At some point, big becomes too big, though. Manufacturers using every opportunity the diesel pickup Power/Tq/GCWR race affords them to pile on weight, more often inn the form of added complexity than in added structural integrity and lessened maintenance requirements, is at best a mixed blessing for the buyer post showroom ooooh-aaaahs.

  • avatar
    brettc

    And the Cruze diesel will do 137 hp and 240 ft-lbs, which is very similar to the disgraced TDI, but about 400 CCs smaller. Hopefully they throw it in the Cruze hatchback as well.

  • avatar
    SCE to AUX

    There is no point in debating incremental improvements in torque if the gearing and – ultimately – the payload/towing are inferior. But I suppose that what TV commercials are for.

  • avatar
    Toad

    Those are crazy horsepower and torque numbers from a 6.6L diesel engine. Not long ago the Detroit Diesel 8V92 (roughly 12L) put out similar numbers with both turbo and supercharging; the modern 13L commercial engines have similar ratings today.

    Beating that many ponies out of that small displacement is not impossible but I would be skeptical about any kind longevity, especially if the engine does any real work.

    • 0 avatar
      dal20402

      You are right to be skeptical. All of these engines have thermal tuning that is intended to enable the truck to climb Davis Dam at the SAE J2807-required 40 mph while towing the heaviest rated trailer without exceeding critical temperatures. Work the engine longer than that, or harder than that, and you’ll find yourself overheating the turbo, the transmission, the engine itself, or all three. Just check out the forums for any of the brands and you’ll see owners with OBD gauges/scanners that report their trucks getting into the red if they’re not very careful with the throttle under heavy load.

      By contrast, that old 8V92 (or its modern Cummins Class 8 equivalent) could make rated power constantly until it needed an oil change and not be the worse for wear.

      • 0 avatar
        mason

        Except nobody I know runs their truck at max GVW at wide open throttle for 11 miles in 100+ degree weather (minimum test temp is 100*F at the base of the test run).

        Anybody who has hauled anything substantial over that pass can confirm the SAE test is the real deal. Not gonna push it harder than that unless your a total tool.

        And really, there is no need for any additional gauges in stock trucks. They already monitor the essentials, coolant, oil, and trans oil in the EVIC. No need for add on’s. I would be skeptical of internet claims, in my experiences the guys that have problems are the ones doing deletes and improper tunes that cause high drive pressures and excessive peak cylinder pressures. I know of several examples of all 3 that get worked on a daily basis and overheating issues are unheard of. Particularly the latest SCR trucks which are back to EGR levels that are similar to pre DPF engines.

        • 0 avatar
          dal20402

          The test is not WOT for 11 miles. It’s however much power is needed to maintain 40 mph with the maximum load, which is far less than WOT for these trucks.

          You need to monitor EGT in addition to what the truck tells you stock. Otherwise grilled turbo may be on the menu.

          • 0 avatar
            mason

            “You need to monitor EGT in addition to what the truck tells you stock. Otherwise grilled turbo may be on the menu.”

            The ECM (at least on the Cummins) monitors post turbo EGT’s and defuels the engine if necessary.

            All one has to do if they really wish to physically watch EGT’s is buy an Edge Insight which plugs into the OBD port. It’s not necessary other than for informational purposes. Cummins knows what they are doing and are not gonna let you hurt the engine.

    • 0 avatar
      DC Bruce

      This is not a “truck” engine that is specified for high duty cycle operation, obviously, in the way that the Detroit Diesel engine you mention is. Of the 3 diesels offered in pickups, the Cummins diesel probably is the closest to being a high-duty cycle engine. Both the Ford, and, apparently, the GM engines are specified at greater horsepower.

      • 0 avatar
        Lou_BC

        DC Bruce – Ford uses the 6.7 in their commercial trucks and it is de-tuned. The Cummins 6.7 is also at a lower state of tune for commercial applications. Even the V8 Cummins in the Titan has higher numbers in pickups. Gm did use the Duramax in larger trucks when they built the Topkick and Kodiak. They were also de-tuned.

        • 0 avatar
          JohnTaurus_3.0_AX4N

          ^exactly, Lou.

          It isn’t just about pure bragging rights. I know people who tow and haul as much as would have required a far heavier duty truck years ago, with one ton and even 3/4 ton diesel trucks.

          What’s funny is to see a Tundra struggling with something it had no business towing. If you hate American trucks but need something heavier duty (and an imported TurboDiesel Patrol truck or Land Cruiser truck isn’t an option), at least now you can buy a Nissan that’s capable of more than half-ton towing ability. Just ignore the fact that it’s designed in Tennessee, built in Mississippi and that its engines are cranked out not far away, its the fact that you didn’t have to get by with some ghastly American over-built penis-extender monstrosity that will pull your 5th wheel camper over the passes like it’s a 16′ aluminum river boat.

        • 0 avatar
          Scoutdude

          It will be interesting to see what GM will have put in the old F-650/750/Durastar. Will it be a MD version of the Duramax or Cummins like in its stablemate?

          • 0 avatar
            mason

            The 6.7 Cummins was the only diesel option in the F650 and F750 from around 2009 when Cat discontinued their highway engine program up until 2015 when they began using their own (Ford) 6.7. The gas option is still the 6.8, which is a real miser at loaded weights. A friend runs one in a service truck that is loaded to near max and with standard (for the gas option) 6.50 gears hes lucky to break 7mpg on the highway.

          • 0 avatar
            Scoutdude

            I think you missed the point which is what will GM have put in their Chevy badged version of the OLD F-650/750/Durastar, not what Ford put in them.

            7 MPG is great for a truck like that if he is indeed running it near max.

          • 0 avatar
            mason

            I wasnt quite sure what you meant by that statement. It’s been confirmed that it will be a Navistar body so logic says GM must be providing the drivetrain or it wouldn’t be much of a joint venture. The Izuzu 6.6L/Allison combo would be similar to previous diesel options in the Blue Diamond trucks.

            GM is also bringing a cab forward MD truck that is a rebadged Isuzu. Engine options will be either an Isuzu 3.0L or 5.2L I-4 diesel engine or GM’s 6.0 V8 gasser.

          • 0 avatar
            Scoutdude

            Well the last I heard GM was refusing to comment on what the engine choices will be in the trucks that carry their badge and Navistar also refuses to say. So it will be interesting to see what happens, especially since GM is also going back to rebaging Isuzus and providing gas engines for those trucks. Both GM and Navistar could use a big MD gas engine that is gaseous fuel prepped like Ford’s V10. Lots of fleets are going that route.

  • avatar
    Vulpine

    Personally, for all that I dislike full-sized pickups used for the last purpose you mention, WS, I think the 6.6L Duramax will actually be working trucks more often than not. I don’t doubt, however, that at least some few will become coal-rolling boy-toys as well. My state and the three states adjacent all have specific laws in place to limit ‘rolling coal’, though they haven’t all been caught… yet.

    I can at least see where such power CAN be used… I live in ‘horse country’ that pretty well spans the distance from the Kentucky Derby, through the Preakness to the Belmont Stakes, so many full-sized trucks around me tend to be hard-working examples of the type… but not all of them by any means. Just as my little Ranger hauls air more often than it hauls goods, I can point out no less than eight full-sized sisters in my neighborhood that carry no more and only two or three that haul materials at any time. They’re used as oversized sports cars more than trucks. I’d rather see them get used as trucks than turned into oversized toys.

    • 0 avatar
      DC Bruce

      I think most of the “cowboy cadillacs” are 1/2 ton pickups. If you want to impress your buddies, go out and get a GMC or Chevy 1/2 ton with the 6.2 liter gas engine in it. Empty, it will do 0-60 in about 5.8 seconds, probably less if you engage the “automatic” 4wd to cut down on wheel spin. None of these diesel monsters will do that because the vehicle they’re pushing weighs, empty, about 3/4 ton more than a half ton.
      My observation is that these big trucks are mostly used to tow big “5th wheel” travel and horse trailers. For that application, they are the right tool for the job.

  • avatar
    28-Cars-Later

    You didn’t build that… wait they did and then revealed it too soon.

  • avatar
    jack4x

    To me, the bigger deal if you actually look at the entire screenshot of the deleted page, is that GM is continuing on at least another year with the GEN 4 6.0 gas engine in the HD trucks. Disappointing for those of us who want the HD frame and capacities, but don’t need the $9000 upfront cost of the diesel plus continuing higher maintenance costs.

    Although it won’t happen, I wish they had the stones to develop a new big block gas engine or even dust off the 8.1 as you still can’t buy a new gas powered truck with more torque than the 460 lb/ft that put out.

  • avatar
    DC Bruce

    Obviously GM thinks that the 6.2 liter 420 hp/460 lb-ft DI gas engine that is available in the higher trims of their 1/2 ton truck lines is not up to the expected duty cycle of a 3/4 ton truck. I have that engine in my GMC in my profile picture. I did not buy the truck to haul air, but it does haul ass. The real reason I bought the truck was to haul a 7600 lb. GVWR travel trailer, which it does really well. After 45,000 miles, I can say that, most of the time, the engine operates well under its limits. In fact, most of the time, it runs at a diesel-like 1750 rpm; and I’ve been coast-to-coast twice and all over the mountains of California, Wyoming, Montana, Colorado and Utah.

    It is worth noting that the 6.4 liter gasoline engine offered as an option in the RAM 3/4 ton (rated at 410 hp and about the same torque) has a built-in “engine saver” that cuts back on engine rpm and power after a certain amount of full-throttle operation (well short of engine overheating). “The Fast Lane Truck” guys discovered this when they tried to run the 7% grade from the Dillon CO to the Eisenhower Tunnel pulling full rated weight. In effect, RAM limited the engine’s duty cycle with software.

    • 0 avatar
      ajla

      I think that GM had a similar “engine saver” built-in to the 6.0L back in the GMT900 era. I don’t think it was as agressive as the Ram’s but I seem to recall it being an issue in an Edmunds test. Not sure if it still exists.

      • 0 avatar
        stuki

        They all have fairly conservative overheating protection built in now. In general, and I’m sure there are exceptions, the higher the specific output, hence the more concentrated potential local heat buildups can theoretically be, the more conservative the protections are. Hence the comparatively sluggish, low compression, large displacement “dinosaurs” powering HD gassers, vis-a-vis those powering generally more intermittent use half tons.

      • 0 avatar
        Lou_BC

        ajla – that would explain what my brother was complaining about a few years ago. He was pulling a 10k trailer with his company 3/4 ton Chevy 6.0 and he’d be revving the guts out of it and it would power out and bog. He thought it was just poor shifting out of the transmission. Engaging tow/haul mode made no difference. He had the local dealer check it and they found nothing wrong with it.

  • avatar
    Lou_BC

    I’ve seen similar quick disappearances of numbers in the past. Since the peak numbers for these trucks can easily be tuned by the factory they all tend to wait to the last minute when releasing specs. They want bragging rights but so far GM has chosen to stay out of the “peak numbers” game with HD’s.

    It is rare to see anyone tow max loads with any of these trucks. Experienced buyers tend to build in some leeway.

    GM who has chosen not to play “peak numbers” claims that the average tow load for a HD diesel is 10k. Ram who chooses not to play peak numbers with 1/2 tons claims that peak average for that class is 5k.

    That does tend to fit with what I usually see. There are guys towing 10k trailers with 1/2 ton p/u’s but ironically most I see aren’t max capacity Ford or GM trucks.

    I do see guys towing massive 54 ft long tri-axle toy haulers but that is fairly rare.

    • 0 avatar
      Drzhivago138

      Any toy hauler or fifth-wheel camper with three axles almost always requires a Class 4 truck, which is only offered in pickup form by Ford (and yes, I know some years of F-450 pickups are just heavy Class 3s).

  • avatar
    dont.fit.in.cars

    I have a 2015 2500HD SRW 6.0 with 68k miles and make multiple runs across the US towing 10k with a pop up camper in the bed at 19k CGVW. Pulled that weight up the Ike at 35 mph at 4K Rpm’s. There is no reason when towing, to run up the Ike at the posted limit than to stress your motor. Chevys 6.0 is perfectly capable, has done everything I’ve asked and while the tranny is not an Allison it holds downhill speed within 2 mph. Gets 9-11 miles per gallon towing at 60 miles per hour.

    The only reason I would be interested in a diesel is range. 36 gallons gets 290-330 miles with gas the Duramax would be close to 500 miles. When gas was 30% less than diesel the cost per mile for gasser was 1.5 cents more than diesel. Crunched the numbers recently and noted I would save a total of 45 dollars a month with the diesel. Not enough for me to switch.

    • 0 avatar
      stuki

      The range discrepancy is, in practice, bigger than that. Larger aftermarket underbody diesel tanks are plentiful and fairly cheap, while aftermarket gas tanks are either flat out illegal, or at least exceedingly rare.

  • avatar
    DenverMike

    The time is right for a return of big blocks. Or at least twin turbo versions of the Hemi, Coyote, etc, for HD pickups.’

  • avatar
    Snail Kite

    Is that enough power to tailgate people in the left lane while going 80mph and hauling a trailer after you install a 10″ lift and big chrome wheels and off-road tires? The people of Georgia need to know.

    • 0 avatar
      Scoutdude

      That reminds me of what I saw last night. A lifted SRW GM HD pickup with a trailer carrying a DRW 3500 GM truck, poorly tied down from the looks of it. Of course it was lifted to the point that even with a big drop ball mount the trailer was at a good angle. He was merging on to the freeway and I took one look at the seriously hurting rear axle trailer tires and put the hammer down to put some distance between us. I looked into the rear view mirror to see the trailer wagging the dog almost into the car that had been behind me. The next glance back showed him pulling over to the side of the road.

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