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Old 04-01-2013, 05:22 PM
WilliamBos WilliamBos is offline
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Join Date: Aug 2008
Location: Innisfil, Ontario
Posts: 57
Cummins 6.7L vs 8.3L in a medium duty truck??????

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.
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Thank you,

Will




Last edited by WilliamBos; 04-01-2013 at 05:26 PM.
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Old 04-01-2013, 11:23 PM
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hosejockey2002 hosejockey2002 is offline
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Location: Auburn, WA
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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.
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Old 04-01-2013, 11:25 PM
WilliamBos WilliamBos is offline
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Location: Innisfil, Ontario
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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.
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Will



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Old 04-02-2013, 06:08 AM
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CLARK LAWN CLARK LAWN is offline
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Location: youngstown, ohio
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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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Old 04-02-2013, 07:15 AM
kawakx125 kawakx125 is online now
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Location: lees summit, mo
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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
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Old 04-02-2013, 11:45 AM
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hosejockey2002 hosejockey2002 is offline
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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.
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Old 04-03-2013, 08:24 PM
zabmasonry zabmasonry is offline
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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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