What RPM range does your truck get the best mileage? This weekend took a 400 mile trip (towing about 5k 200 miles) I noticed that if I keep it around 1800 rpm it would get the best about 17.5 off of the overhead. It seems to me that maybe this new tranny lugs the motor to much, just an idea. I have been trying to keep the truck in 4th gear around town it seems to help a little.

 

Lugz alot. AV flash might help out, my truck is going to dealer for recall tonight but I already have AU flash. As for mpg, i think 18-2000 would be nice unloaded. Cummins site says 2150 rpms for optimal mpg. Optimal performace with a load is 225--2400 rpms. I usually cruise from 55-65 in 5th gear. up to 75 mph in hills in 5th. Flatland driving in 6th around 70-75 mph which is still kinda low. Shoulda got 410s. I wish i opted

 

Why do you think you should have got 4.10's?

 

Cause I do nothing but tote 20k. 410 will keep in higher rpm range

 

I'm a bit confused. A lot of people seem to think the tranny lugs and hence not optimal for best mpg. Yet others seem to think that a lower RPM is better and hence they get bigger tires. Does anyone have any real information on if the higher RPM range or lower RPM range is the most ideal for mpg on this truck?

I don't drive this truck that many miles and so far 1/2 of my 1400 only have been towing. Maybe the guys that drive the cr@p out of them and tow for a living would know best?

 

All info I told you is directly off cummins engine web page. You beleive what you want. THIS IS CUMMINS INFO

I have played the whole best mpg game at different rpms, different gears. To be honest, these trucks get such horrible mpg as it is stock, dont bother wasting your time changing your rpm habits cause you wont notice any difference..

 

Sorry, I don't agree. If you are lugging the engine you are probably creating more black smoke, even if you don't see it coming out of the tailpipe because of the DPF. That means more particulates for the DPF to capture hence it will start to fill up quicker and more often. That means more frequent and possibly longer regens. The biggest reason for reduced MPG compared to the 5.9's (besides larger C.I.) is the fuel injected into the exhaust stroke to raise the exhaust temperature via the catalytic process in the NOx unit. This significant temperature increase is what burns the particulates out of the DPF.

So, in theory anyway, less lugging = less particulates = fewer/shorter regens = slightly improved fuel economy.

I don't think Dodge would create the AZ flash just because they're nice guys. To my knowledge there hasn't been a lot of people complaining about bad shift programs, but everyone with a 6.7 is complaining of poor MPG. That tells me (maybe wishful thinking?) that Dodge is looking at every opportunity, no matter how small, to improve MPG by optimizing the emissions system performance. If the AZ flash helps keep the motor running in a more efficient power band too, then so much the better.

I believe that Dodge monitors these types of forums as well as inputs from customer complaints and their dealer network. I believe that Dodge, working with Cummins, will continue to improve the performance, functionality and MPG of the 6.7's. It may be little by little over the next year or two, but they will get this thing optimized.

 

Newbie here...could you give me the Cummins web page URL so that I could read this myself? I made a 60 mile trip on the 4-lane last night...Steeler Monday night f.ball game...with the tranny in 5th...not 6th. Did this by accident...forgot to allow the upshift after downshifting to slowdown when entering the toll booth. There was too much BS'g going on inside and I didn't notice the truck running at about 2150 rpm's until it was time to get off of the pike. The readout showed 13.8 mpg at the time. I made sure that this didn't happen on the way home...ran the same speed, only in 6th this time...turning app. 1850 rpms. The mileage readout increased to 14.8...and this included the Pgh. city driving and the climb back up the mountain. I'm having trouble believing that the engine burns less fuel when it's turning a higher rpm.

The truck is new...2008 Quad cab...6.7 auto...3:73's...less than 1200 miles. I love the power...mileage is at 12.9 actual (pen and paper), which isn't what I hoped for but it's 2+ plus better than the '99 V10 that it replaced. The V10 kept improving until it hit 10K miles...expect that this will do the same. And did I say that I love the power?

 

Traditionally, the BSFC sweet spot for the CTD has been 1800-1900 RPM... it's possible that it's higher on the new 6.7L due to regen.

BTW - my '98 V10 knocks down 14mpg on the interstate with 250K miles on the engine.

 

http://www.powerspec.cummins.com/sit...ng/gearing.htm

put in your parameters and see what you get, 2150 rpms, don't tow below 1900 rpm

 

I too think that a bit more rpm helps due to less smoke being filtered. In my truck i get better milage from running about 1400 rpm (70-75mph) vs 1250 (60). I think these trucks fuel hard on bottom in order to get the turbo to spool. People with the dpf removed comment on amount of smoke coming from these engines at low boost as being pretty high

 

Interesting....

Thanks!

 

So with the 3.73's while towing and empty I should put the 68FRE in 5th gear and lock out 6th?

 

I never said you get the same mileage, i basically meant you wont see a difference worth while. And its the av flash. I agree with ya on the dpf crap and regens, but when towing, you may see 20 miles extra to the tank. What do you consider lugging?????? I would consider a true nasty lug anything under 1800 rpms which im never under. I try and stay above 2000 rpms. but i would still consider a lug between 18-2000 rpms but not noticeable in mpg. BUT YES IT DOES AFFECT. anything below 1800 rpms it will just downshift, and if you stay below 1800 rpms driving with a load, your just gonna burn your tranny

 

better mileage at higher rpm's due to the fact that the engine is turning faster but is not working as hard..... there is a limit though....ya know? that sweet spot....you just have to find it.....my c&c doesn't like to go higway anything over 2k rpm's and get over 14....keep it at about 1900 and i'll run 17mpg all day long.....