Cummins 6.7L vs 8.3L in a medium duty truck??????

Discussion in 'Trucks and Trailers' started by WilliamBos, Apr 1, 2013.

  1. WilliamBos

    WilliamBos LawnSite Member
    Posts: 57

    A friend of mine is looking at getting back into RV hauling, and wants some help on engine Choices.

    The email states a FL, but he will most likely go with a KW T270.

    See below...


    Here's what I sent them: Used Freightliner so I don't have to argue
    with doe heads about a Paccar PX6 and PX8 being a Cummins.



    Specing a medium duty truck for my RV trailer logistics company. Truck
    will likely be a Freightliner M2 with an Allison automatic
    transmission. It will weigh roughly 11,000 pounds and the biggest
    trailers I haul are between 12 to 14,000 pounds. I'm wondering, will
    the 6.7 (325 h.p./750 torque) be more fuel effecient than the 8.3 (at
    1000 torque) or should I go with the bigger engine. I'm trying to run
    as efficiently as I can, but of all the RV and trucking forums I have
    posted on and dealers I have spoken to, I can't get a clear answer on
    this. I like that the 8.3 is a wet sleeve engine and more robust, but
    I don't want to give up fuel mileage. Thank You.
     
    Last edited: Apr 1, 2013
  2. hosejockey2002

    hosejockey2002 LawnSite Bronze Member
    Posts: 1,195

    I don't know about the mileage between the two motors, but I will say that while the 6.7 Cummins may be the king of the hill in pickup trucks, in an MDT it is a base engine, kind of like getting a pickup with a V6. The bigger 8.3 will likely last longer, and if your friend decides to switch from lighweight car haulers to something heavier the truck will be up to the task. If he's really concerned with mileage, if I were him I'd forget the Allison and get either a Smartshift-type automated manual or a full manual. Both should get better over-the-road mileage than an Allison.
     
  3. WilliamBos

    WilliamBos LawnSite Member
    Posts: 57

    Thanks. I will let him know this. If Mack Offered an MP7/mDRIVE in a medium duty chassis, betting that would be the way he would go.
     
  4. CLARK LAWN

    CLARK LAWN LawnSite Silver Member
    Posts: 2,526

    Definitely go with the 8.3. At the dealer I work at we get those kind of trucks in all the time. Medium duty with a DT (466) in it and the engines are beat to death. The owners spec them with the smaller engine for fuel economy and end up beating up the engine and spending more on repairs than they are saving on mileage.
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  5. kawakx125

    kawakx125 LawnSite Bronze Member
    Posts: 1,121

    i have a 6.7 in an 08 ram, it's a beast but i can see how it might be underpowered in a larger truck. if he's only pulling 12-14k lbs in an 11k lb truck he's only looking at 25k lbs max. guys on cumminsforum swear that the 6.7's are more than capable of pulling that weight in a pickup all day long, and plenty have the scale slips to prove it
     
  6. hosejockey2002

    hosejockey2002 LawnSite Bronze Member
    Posts: 1,195

    It's not that the 6.7 would be underpowered. 350hp/750 torque will move a light load (25K) very well. It's more about duty cycle and longevity. The 8.3 will go many more miles between major repairs and being a wet sleeve engine can be rebuilt inframe. It's just better suited for a commercial over the road application.
     
  7. zabmasonry

    zabmasonry LawnSite Senior Member
    from C. VT
    Posts: 314

    Problem with the t270 if memory serves is that it has pretty limited cooling capacity, I assume that it can be purchased with the 8.3, but it may be very derated.
     

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