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Discussion Starter #1
Anyone out there with a new 6 speed transmission have any information about the recommended shift rpm's for the 600 engine? In the short time I have been driving it seems like the optimal rpm's for each gear is 2000-2100 rpm's. Keep in mind this is with a empty truck and no trailer. Anything above 2100 rpm's it seems that the turbo spools faster but you don't get much speed advantage out of the extra rpm's. I'm sure with some weight in the back or a trailer the rpm shift points would change but for now I am running with a unloaded truck. Any information would be greatful.
 

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Mine is a 555 so it might not be relevant. Most shifts seem comfortable around 2,300rpm's for me. Less than that and there seems to be a moment where accelleration is paused and then picks up. That is under load.


Solo I do the same but skip a gear, following a 2-4-6 shift pattern. Any less rpm and there is too much rpm drop for me to be comfortable.
 

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I assume your truck is brand new. It's going to be very tight and somewhat reluctant to rev in the upper rpm range. I noticed this when my truck was brand new.


I usually shift around the 2,300rpm, seems to be the sweet spot for the engine and tranny, anything above this doesn't gain very much. Probably caused by the low flow rate from the stock muffler.


MikeyB
 

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Discussion Starter #4
Yes, the truck is brand new, well 700 miles. It is reluctant to run in the high range ie. 2300 rpm and above. I don't see much gain either by going higher in rpm's. What range aren't you comfortable with hoot? 500-700 or below that?
 

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I too, couldn't find shift point or upper RPM cruise limits, so I asked Cummins. The answer was:


"You can use the full RPM range to pull your load down the highway. The engine will give you the best MPG between 2000 & 1600 RPM. You may need to use higher RPM in the first few gears to get your road speed up but when you get to cruise speed put it in a gear that will let you cruise in 2000 RPM range."


With a 6 spd manual & 4.10 rear, 70 mph is about 2300 rpm, so I reckon 60-65 towing puts me in the recommended MPG range. Just like the rest of you, shifting at 2100-2300 feels right. Taking what Cummins says at face value, it appears that it won't hurt the engine to turn 2900 or so for extended periods if one needs to in 5th or 4th gear going up mountains.


2004.5 White Laramie 3500 Dually w/ Line-X & PacBrake. Mileage, who knows? Only have 700 miles, but it sure beats the 4-bbl 454 I had. Gotta go get Nerf Bars.... So far so good!
 

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CTD 600 said:
What range aren't you comfortable with hoot? 500-700 or below that?
I only have two pedals. One makes it go the other makes it stop
Edited by: hoot
 

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Discussion Starter #7
Oh geezzes!
Thanks Hoot


OregonAggie said:
I too, couldn't find shift point or upper RPM cruise limits, so I asked Cummins. The answer was:


"You can use the full RPM range to pull your load down the highway. The engine will give you the best MPG between 2000 & 1600 RPM. You may need to use higher RPM in the first few gears to get your road speed up but when you get to cruise speed put it in a gear that will let you cruise in 2000 RPM range."


With a 6 spd manual & 4.10 rear, 70 mph is about 2300 rpm, so I reckon 60-65 towing puts me in the recommended MPG range. Just like the rest of you, shifting at 2100-2300 feels right. Taking what Cummins says at face value, it appears that it won't hurt the engine to turn 2900 or so for extended periods if one needs to in 5th or 4th gear going up mountains.

Thanks for the info OregonAggie. I have found that the motor doesn't hesitate as much now that it has more miles on it. Climbing a hill, I have gone to 2600 rpm's in 3rd or 4th and nothing noticible has happened. I think I am just feeling the torque up to 2100 HP and then feeling the HP after 2100rpm's.
 
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