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-   -   3.21 vs 3.92 mpg? (http://www.ramforumz.com/showthread.php?t=98678)

09ramhvac 12-13-2011 12:53 AM

3.21 vs 3.92 mpg?
 
Has anyone ever switched there 3.21's for 3.92's? and if so what did it do your mpg on the highway? I have a 09 2wd crew with 20" wheels, I do mostly highway driving but where I live theres alot of small hills and it seems like my truck rarely stays in overdrive when climbing. I think my truck is geared way too high and I personaly think that if I were to switch to 3.92's the truck would stay in overdrive longer and work less to climb these small grades resulting in better mpg. But I would like to hear from someone who has first hand experience with this before I spend the money on the swap.

916Timmy 12-13-2011 07:39 PM

I am waiting to do at least a 4.10 swap, but I can get almost 24 MPG on the highway if the speeds and conditions are just right! I got 23.6 on a 400 mile trip to Kansas with my 3.21 gears

09ramhvac 12-13-2011 10:09 PM

On a reasonably level road I can get 22-23 mpg. But on the loop I take to work I get anywhere from 18-20 mpg driving super conservatively. But I think with 3.92's I would be using less throttle. I had a ranger with 3.73's pulling 33's I put in 4.10 and I gained 5 mpg. Even though my rpms were higher I was using less throttle. I know there 2 different trucks but I think the same theory applies.

whatroads 12-15-2011 06:16 PM

I've got QC 4wd w/ 17 inch wheel and 3.92. If I REALLY keep my foot out of the skinny pedal I can get 18. I mostly average 16-17. This is not using the milage display. All hand calculated

09ramhvac 12-15-2011 10:42 PM

Quote:

Originally Posted by whatroads (Post 674537)
I've got QC 4wd w/ 17 inch wheel and 3.92. If I REALLY keep my foot out of the skinny pedal I can get 18. I mostly average 16-17. This is not using the milage display. All hand calculated

How is it on small grades or rolling hills? does it lose speed and constantly downshift. Or are you able to accelerate up hills in overdrive?

whatroads 12-16-2011 05:24 PM

At one point I had a 2005 QC 2500 Hemi 4x4 w/ 4.10. My 2011 QC 1500 4x4 w/ 3.92, (similar gearing), and the newer more powerful Hemi downshifts less than my older 2500. In addition to more torque I would expect my 1500 to weigh somewhat less than my solid axle 2500 did

I have a hill, close to my house, that has an 8% grade, (according the the warning sign). The hill is about 1/4 mile long. The 1500 does not downshift or even slow down. It does kick out of "ECO" mode where I assume all 8 cylinders light up

Towing my trailer? Yes the tranny kicks down and the RPM goes to 45-4800. This is perfectly normal for a gas engine towing a 31ft 7-8,000lb trailer. The Hemi is very happy to run in this RPM range. Again, the newer Hemi feels stronger, pulling my trailer, than my previous 2005. Likely the higher torque in the 2011


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