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Old 08-28-2005, 05:37 PM   #1
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Thinking about slowing down for better milage on long trips due to fuel prices and was wondering at what point would I be lugging my 03 HO CTD with the 6 speed. Am I better to run her at at least 1800 rpm to get peak torque and horses in fifth gear at 55 mph or drive 55 mph in 6th gear at 1600 +/- rpm? I pull a 26' TT that weighs about 5500 lbs. Am I lugging her at 1600 rpm?
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Old 08-28-2005, 05:37 PM   #2
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Thinking about slowing down for better milage on long trips due to fuel prices and was wondering at what point would I be lugging my 03 HO CTD with the 6 speed. Am I better to run her at at least 1800 rpm to get peak torque and horses in fifth gear at 55 mph or drive 55 mph in 6th gear at 1600 +/- rpm? I pull a 26' TT that weighs about 5500 lbs. Am I lugging her at 1600 rpm?
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Old 08-28-2005, 07:00 PM   #3
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It's hard to say with your setup. What do you normally run about 1800 to 1950 pulling my 5vr or empty at about 65mph. I'm also running an auto.
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Old 08-29-2005, 04:23 AM   #4
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If the truck won't accelerate under load, it's lugging. The primary consideration with a 6-speed at 1600 RPM will probably be exhaust gas temperatures. If the engine is under heavy load at those low RPM's, EGT's will be very high. Do you have a pre-turbo pyrometer installed? If so, that would be an excellent indicator of when you need to downshift.

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Old 08-29-2005, 09:18 PM   #5
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Echoing what Rusty said, if there is not a definite and smooth acceleration when you apply more throttle the engine is lugging/laboring. This is very harmful to- well all the engine. When using cruse control lugging may go unnoticed unless you monitor EGT faithfully. I think the low end of the torque curve for the Cummins B5.9 is 1600rpm, below that the engine is not performing to it's potential. That is one reason the Dodge(CTD) AT torque convertor has a stall speed of 1600rpm.
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Old 08-30-2005, 06:39 AM   #6
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When I got my truck, I asked Cummins about proper operating range. Essentially they say don't load the engine below 1600, and don't pull in a gear so high that it won't accelerate when floored.

I'll just paste in what they gave me, so you can read what Cummins says for yourself...


Solution:

Thanks for your Email message.

In the Dodge application, the rpm of the advertised or maximum rated power of the engine is 2500 rpm (prior to 1996 models), 2600 for 1996 and newer models with 12-valve manual transmission and 2700 rpm for 24-valve. Peak torque is reached at 1600 rpm on all models. The Maximum Full-Load Governed Speed is 2800 rpm for 12 valve and 3200 for the 24-valve. The Maximum No-Load Governed Speed is 2950-to-3300 rpm (3500 for 24-valve).

Therefore, your normal operating range for the engine is between 1600 (peak torque) and rated rpm (2500-to-2700, depending on your model). These engines should not exceed 2800 or 3200 rpm downhill (depending on model year), under load, since that is the governed speed of the engine. At no load (i.e., if you were to push the accelerator to the floor and hold it, sitting still in neutral), the no-load governed rpm is about 10 percent over the full-load governed rpm.

The engine is designed for maximum torque or twisting power at lower RPM (1600 rpm), for hard pulls on long grades. The torque curve of the engine is nearly flat from peak torque (1600 rpm) to rated power (2500-to-2700 rpm), however, torque does drop off slightly near the rated power rpm. Typically, the 'sweet spot' rpm for cruising would be about midway between peak torque and rated engine rpm, however, any rpm between peak torque (1600 rpm) and rated speed is fine and will not harm the engine. Overspeeding above rated speed and lugging the engine under load below peak torque is not recommended.

Also we mention that on downhill operation, the weight of the truck and any load you have on it, or towing, will cause the rpm to exceed governed rpm. Even though the engine is governed while under power, the load can push the engine beyond its rated speed. We would not recommend going too much over the no-load governed rpm or you could cause valve/piston contact, which can cause major engine damage.

Any rpm between peak torque (1600) and full-load governed rpm is acceptable and will not harm the engine. However, if you are concerned about fuel mileage and long engine life, then the lower rpm is recommended. At higher rpm's, the engine uses more fuel and all internal components turn faster and wear out quicker, which will shorten the life of your engine. There is less horsepower and torque at maximum rpm and the only reason to run the engine at maximum rpm would be for higher road speeds.

For the best fuel mileage, Cummins engines should be operated between peak torque and rated speed. Do not lug the engine when running in this RPM range. What is "lugging"? Lugging the engine is when, at cruising speed, the engine is accelerated and it will not increase the vehicle speed. Also, lugging is operating the engine, under full load, below peak torque rpm.

We do not have information about shifting into or out of overdrive in the Dodge application, since Dodge designs and supplies the transmissions for their products.

If your engine is still within the Dodge warranty period or you need information about the Dodge Ram truck, please feel free to use the Dodge dealer locator or contact Dodge: (http://www.4adodge.com/frameset_main.html?dealers/index) on the Dodge website (http://www.4adodge.com/).

We thank you for your interest in Cummins products. Please let us know if you need assistance in locating the nearest Cummins-authorized Dealer or Distributor Service Provider. For assistance in locating a Service Provider, feel free to use Cummins North America Dealer Locator, which can be found on Cummins website:
http://www.cummins.com/service_locator/index.cfm

Please let us know if you have other questions and if away from your computer or have a time-critical request that needs more urgent attention, feel free to call us toll-free (from North America) at 1-800-DIESELS (343-7357). Customers may also call Cummins switchboard 1-812-377-5000 (worldwide toll call) and ask for the "800-DIESELS Call Center" for assistance.

Email direct: powermaster@cummins.com

Regards,
--
Powermaster
Customer Assistance Center
Cummins, Inc.
Columbus, Indiana, USA


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Old 08-31-2005, 04:15 PM   #7
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Jeff
Great info
thanks
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Old 08-31-2005, 06:40 PM   #8
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Everything said above about lugging a Cummins is true. My concern is more with the statement "slowing down to save fuel." I've had 1994 12 valve, a 1995 12 valve, and now a 2004 24 valve. Each one of them got worse fuel mileage at slower speeds than when I ran within the specified power range. By the way I won't tow without an Exhaust Gas Temperature Gauge. Cost a little over $100 and could save a $5,000 engine.
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Old 08-31-2005, 10:40 PM   #9
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Mine seems to get better milage the slower I go, but with 3.73's I drop into 5th below 55 mph to stay above 1600 RPM...
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Old 09-02-2005, 05:57 PM   #10
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Thanks for the info Guys. I think I'll run my Cummins a little higher in rpm's or in fifth gear when towing at 55. Just a few mpg's more can add up a lot quicker at todays fuel prices. Do I need to get a hole drilled and tapped for a temp probe for exhaust temp guage?
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Old 09-04-2005, 01:42 PM   #11
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Actually, I just put in a pyro just the other day.

I went with the new isspro that matches the factory dash, in DC's SRT-10 A-pillar, and it really looks clean/factory.

I don't know if the pyro is an absolute must on a stock engine, but it is kind of nice to have.
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Old 09-06-2005, 07:58 PM   #12
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I have a dodge CTD and I babyed it keeping the speed down 55-60 from so cal to past reno nev. Checking milage then just stood on it from outside reno through winnamuca and to boise. Going 65-70 and it got just as good milage not babying it.

Going easy on the cummins didnt seem to help milage. Just run it.

I did get stuck behind a big rig going 45 mph up 95 in idaho toward sandpoint and I had to keep it out of OD and got alittle better milage going 45 but I think that was less wind resistance on my camper at low speed.
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Old 09-10-2005, 04:15 PM   #13
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I seem to get at least 10% increase in MPG at 60 vs 0 mpg solo or towing.
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Old 09-16-2005, 08:02 PM   #14
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The 03 ho cummins reaches peak torque at 1400 rpm. Should be fine cruising 1600 rpm on the flat or slight hill while towing.I too cruise at 55-60 for milage with my 04 with a 6 speed and downshift when it gets steeper or I need to accelerate faster pulling 6-7000 lbs.
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