dhe9

chris,
what does your fuel economy look like with those 3.42s? wondering because i have ordered a CTD with the same gearing and the G56.

david,
socal

sheriffav8r

Yeah, I'm not worried too much about the 1800 rpm thing. Cummins said 1900 for the 5.9 applications, but it runs just fine below that while cruising. Again, that's for medium duty applications and just something to shoot for. The new engine starts pulling full torque so low I don't think it matters much (1650rpm ish). I was just wondering if there was a spot the autos like to roll at. Like I said, my 5.9 loves 2000rpm and it just purrs at that speed; unfortunately that speed is 80mph. Man, it'll go from 80-110 in about 4 seconds. But I digress....

DirtEater

If peak torque is 1500-1600 rpm's, what's the big deal with 1800? Is it simply to help aid in the regen process, maybe?

Blake Clark

I would say so. Higher EGT's less active regen....

DirtEater

Yeah, that's what I was thinking too. Funny how something labled Heavy Duty is so finicky to the point where maintenance is a finesse thing.

Blake Clark

I agree but how you gonna fight big brother.

Only way you can win is to eat your warranty and delete it.

Then you actually have a truck again.

signature600

So far, about 16-17mpg indicated, hand calculated at about 15-16 mpg, combined driving. If I spend a lit of time on country roads around here, I can push it up over 18mpg hand calculated.

Leaving this afternoon for my first long trip unloaded, 575 miles one way, so we'll see what it does. 9600 miles so far.
Chris

dhe9

do me a favor and post your mpg results after the trip? i ask because even tho i do not have my truck until aug 15 i will need to make a trip to arlington, texas towing a trailer with a motor cycle and will be interested to hear your results. from the west coast to texas the trip is about 1400 miles one way.

thanks again.

david
socal

DirtEater

Now I'm wondering how Dodge and Cummins coordinate these gear ratios along with desired rpm. If Cummins says not to cruise below 1800, that can be diifcult. I just came off the in-town freeway where the speedlimit is 60 and 65 depending on where you're at. At 65 mph, my rpm's were about 1650 and at 70 they were about 1725-1750, this is with 3.73's, 6 speed auto tranny and stock bologna sized tires. What, are we supposed to say the heck with 6th gear and cruise around in 5th? Just doesn't add up.

I knew I should have just ordered a truck again, like I did in 2005 and got the 4.10's. But I settled for what was on the lots.....nothing but 3.73's.

sheriffav8r

Yeah, I think everyone will find that cruising at 1600-2000 is what is going to happen most of the time. Again that PowerSpec program is made for medium duty trucks that have different gearing and much different weights.... I originally brought this up because I know I will be pulling a heavy fifth wheel and wanted to pick the right gearing for cruising at 70mph. My 5.9 is definitely on the backside of the power curve at 70mph turning only 1750rpms. The 6.7 makes torque a LOT earlier so this shouldn't be a problem with either 4.10 or 3.73 gears....

DirtEater

Hmmm, guess I overlooked the part about the rpm range being for the heavier comm. trucks.

signature600

575 miles one way, didn't fuel up before I left, had about 65 miles of city driving on the tank, and about 15 miles of "hard driving" my brother and some of my friends were doing saturday night Still averaged about 17.6mpg on the way up.
Coming home, same story, had a few miles of city driving, about 50 on the tank, and after 265 more miles on the highway, I stopped and topped off the tank to get home, 17.8mpg.

Last tank, 300 or so highway miles, and 300 or so city/county road miles, the dash is reading 18.7mpg, so when I fill up tonight, I'm expecting right at 18mpg.

I'm happy with that for my 8000lb, 11,250 mile truck with all emissions equipment intact.

I've grossed 24K lbs with a 48' enclosed trailer, pulling 72mph at 1700RPM in 6th, no problem. I let it downshift on the hills, but running on the flat lands and smaller hills was no problem. Running 5th gear at 2100-2200RPM the truck doesn't even work. As always, I'd like another gear in between them, but I've been told I'm too picky

Chris

sheriffav8r

What gear ratio and tire size do you have?

signature600

3.42, 68RFE, and stock 265/70R17's

Chris

charles.sulliva

I'm trying to sort the MPG mystery myself, to maximize my dollars. The other day I reset the meter, got on a state road and was just over 1500rpm and right at 60mph, meter was giving me 23.4 mpg. This was nice, flat road without traffic where people cause you to change lanes, speed up, slow down, etc.

Today I jumped on I75 for about 20 miles, too much traffic, too much moving around, too many inclines, mileage was in the 17s. I was trying to evaluate the mpg at around 70mpg and around 1900 rpm, roughly. Couldn't get anything consistent due to traffic and incline.

This is also why I prefer driving at night, less traffic, less hassle.