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Old January 26th, 2010, 09:40 PM   #1
kkodet
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Default Where is the cummins rpm sweet spot?

For those of you who run cummins motors, maybe you can help.

I've got a 12 valve 1990 non-p pump cummins I'll be swapping in my suburban with an NV4500 and solid axles.

My plan for this rig is to be mainly my tow rig, but also be a mild family wheeler.

Where do you like to see your cummins running for RPMs:

For towing?

For driving daily?

For the best fuel mileage?
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Old January 26th, 2010, 10:42 PM   #2
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2250
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Old January 26th, 2010, 10:48 PM   #3
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Quote:
Originally Posted by trooper View Post
2250
For what? Towing, DD, wheeling?
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Old January 27th, 2010, 12:33 AM   #4
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i run damn near 2k which puts me at 70 72 with 285x75 bfg at with a ats 47re tranny
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Old January 27th, 2010, 12:53 AM   #5
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I set the cruise on 80 and relax. *lol*
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Old January 27th, 2010, 01:11 AM   #6
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1,800 is what I thought for MPG's

But what do I know...I'm running a 12V Crewcab on 40's with 4.10's and a 47RH auto
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Old January 27th, 2010, 07:08 AM   #7
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same engine, completey different machine, but most of the heavy equipment I work on with the Cummins has the high idle set at about 2200-2250...this is the point (in these applications anyway) where the high points of the torque curve and fuel efficiency meet..granted, there are other factors (hydraulic p/q curve, engine pull down, exhaust noise level, etc) but every engine will vary slightly anyway, so this should be a good starting point for you

for times of less load (daily driving, etc) and MPG is the biggest concern, I would think somewhere around 1800-1900 RPM would be a good place to be
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Old January 27th, 2010, 07:50 AM   #8
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About 1900 is the sweet spot on a 12v. That is where it makes most of its torque and runs efficiantly (sp?).
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Old January 27th, 2010, 08:22 AM   #9
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Look at what most dodges with a cummins had for gears, 3.55.
Shoot for something around that and the rpms will be fine.
One other tip, get a 3k governer spring for that VE pump, the extra rpms will be helpfull especially if you go with lower gears.
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Old January 27th, 2010, 08:26 AM   #10
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My 95 with 3.55 gears gets around 17 mpg if i can keep it around 1800-1900 rpms
thats doing 70-75 mph. pulling at the same rpms i have seen 13-14 mpg
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Old January 27th, 2010, 08:36 AM   #11
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2000 for MPG, and its a 6 speed so i call the shots lol.
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Old January 29th, 2010, 08:33 PM   #12
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17-1900 for best mpgs/dd and about 2000-2200 for towing. i dont care what anyone says over 2000 will not get you best mpgs in a cummins
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Old February 1st, 2010, 12:12 AM   #13
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the engines are designed to run between 1200 and 1800. thats where the most power and torque come out of the cummins. when i was at the dealership thats what they recommended. dont lug the motor though, on the big motors it causes fretting of the block. never seen it on a "B" but it could happen
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