Debate: Do 4.10s get lower milage than 3.54/3.73s?

[Posm]

After reading many, many mileage posts on the 2nd and 3rd gen sight, I can not see much, if any difference in the MPG of the rear end ratios. I do see a considerable difference in those that want to run upper 70MPHs as apposed to closer to 70.

The 3. 73with the 17 inch tire is the same final ratio as the 3. 54 with the 16 inch wheels. There is nearly as much difference between the auto (. 69 4th gear) and the 5 speed ( . 75 5th gear) as there is between the two rear choices. Should the auto even come with the 3. 54/3. 73 ratio?

Many posts have stated that peak engine efficiency comes where peak torque and Hp are closest. That would be in the 2500 RPM range. A while back the TDR mag had fuel consumption for a given brake HP on a chart. The consumption was flat from 1800 to about 2400 if my memory is correct. Do not confuse driving at these RPMs with brake HP. The Dyno can keep a constant load throughout the range while load goes up considerably as speed increases because of wind resistance.

What RPM is best?



Let the debate rage!!!

 

[Dkevdog]

I have the 4:10's now, and I know my mileage is lower than guys running 3:54's. Howevere, I know of one Member that comes to mind, Garrett (Big White Beast) who runs a utility body on a 3500. As little sense as it makes to me, he claims to have not seen any difference in MPG- and he tried 3:54 - 4:10 and finally ended up with 3:73.



Like anything else, I'm sure that driver has the biggest influence on MPG. I was considering going to the US Gear overdrive for an increase in MPG. Surprizingly to me, many members chimed in saying there was a slight, if any improvement in mileage. It was attributed partially to the resistance of the extra gears and drivetrain.



So I am currently shopping for a 3:54 trade. If I end up with a mileage improvement, I'll be happy, but that isn't the only reason I'm looking to trade. Those with the best mileage I've seen reported are coming from trucks with the 3:54's. But then again- are they driving 55 to get that mileage and driving the truck very modestly?



Kev

 

[Mathew Clausen]

I would like to clear up what seems to be a common misconception regarding 16" vs 17" tires. From the michelin specs - revs/mile for factory 16" vs factory 17" (LTX - A/S)



265/70-17 => 657 revs/mile

265/75-16 => 654 revs/mile

245/75-16 => 679 revs/mile



So - the stock 17" tires are actually slightly smaller (very slight) than the stock tires from an '01/02. But - they are larger than the factory 245/75-16 that came on earlier (I think pre2000?) rams.



As for mileage - I agree that the biggest factor is probably surrounding conditions such as headwind (big factor), trailer, canopy (not good for mileage at speed), 2wd/4wd, speed (probably the biggest factor - its not loss in engine efficiency that hurts you at 80 - it is the air you are pushing!), winter fuel, tires (you run tall aggressive wide tires - you pay), how hard do you accelerate - there are so many variables that it will never be possible to make good comparisons.



Also - most engine efficiency curves are shown at full load - part load curves are hard to find. These will be different than full load - and you generally cruise on the fwy at much less than full load.



Mathew

 

[boonsur]

Another Argument...

The mileage difference is probably minimal, and the 3. 73's are probably enough (to tow with) for just about anybody, unless you're pushing the high end on weight, or pull a lot of hills. I simply think the 3. 73's "feels" better at 75+ MPH. I know the Cummins can run high RPM's all-day-long, but my new truck just seems far more relaxed than my old with 4. 10's.



An abstract factor I think about, is the increased life expectancy - LESS CYCLES TO ACCOMPLISH THE SAME DISTANCE. I really thought about this with my 4-cylinder Neon, which spun about twice as many RPMs. This means life expectancy was halved before we even consider design superiority.

 

[Ted Constantine]

I don't see a difference at speeds up to 70-74mph. Above that the 3. 54 rear ends have an advantage but still drop off the MPG as our trucks are only slightly more areodynamic than a brick As long as you are in the efficient range of the rpm curve there should be no difference. i run 295 tires so my axle ratio is some where around 3. 94 if I remember correctly (it has been a while since I calculated it) with the 6spd and living in the east with 65 being the speed limit I usually jsut drop it on 2000 rpms and am still passing people on the highway. The 4. 10 keep me in the sweet spot all the time.

 

[Dkevdog]

My only complaint with the 4:10's and 6 speed is I feel like I'm always running out of engine. I know, like has been said the cummins will handle the high rpm without a problem, but as boonsur points out, my truck seems like its nervous at 2400 rpms on the freeway. That's the reason I'd like a set of 3:54, to gain a little more MPH before running out of RPM . If I can't find a donor to swap with, I'll probably buy the 3:73 setup . I think that would be the best combo.



Kev

 

[Posm]

One of the things that I have done is to ignore the spedo and run the engine up to where it sounds "good". My truck sounds best at 2250 to 2300 RPMs. I also have noticed anything below 1800 and it sounds like it is lugging. I changed back to stock tires ( from 235/85s to 245/75s) and that 5% makes a lot of difference in power. I cannot imagine having an auto and trying to run 55 MPH. No wonder they try to hunt gears, they are close to 1500 RPMs. A 5 speed ( . 75 final ratio) is bad enough at 45 to 55 MPH let alone trying to "dog" four gears at this popular speed.

I rarely run over 72 or 73 MPH and wonder what kind of mileage penalty I would pay by going with a 4. 10 rear on my 04 6 speed. I know the towing difference would be huge, given the extra gear and the lower ratio.

Towing is also affected by wind. I pull large round hay balers 10 to 15 K per year and can tell you a 6500LB hay baler pulls harder at 70MPH than a 13K goose neck with a cab high load.

 

[Boonieman]

I had a 2001 auto with 3:54's and easily got 20-21 MPG. I have 1900 miles on my 2003 HO 6-sp with 4:10's and I'm calculating 18 mpg at this time. And... it's hard to get used to the higher engine RPM's for sure!

 

[athompson]

My only complaint about the 3. 54s and the 315s is that overdrive is still geared too low. I'm always wanting to shift into 7th when I get to about 65mph. I cannot even imagine how I could handle 4. 10s with anything less that 44" tires.



Note: I don't tow. Most of my driving is in town at between 900 - 1500 rpm and I get between 17 and 18 mpg. When I'm driving the freeway exclusively, I drive at 1700 - 2000 rpm and get just over 18 mpg. Off-road mileage is unpredictable.

 

[Barry]

The final drive ratio of the Auto/410s is 2:82 and final on the Man/3:54s is 2:79. As you can see, they are almost identical. Unless you just plan to drive the truck to the grocery store, I would not recommend the Auto/354 combo.

 

[Dean Upson]

When I switched from 3. 54's to 4. 10's in 1998 I really had a hard time with the noise at highway speeds. I did get used to it, plus my senior hearing is more forgiving as time goes by . I have the 4. 10's on my '03 and the engine is so much quieter that I really don't have an issue with the noise. The larger stock tires have dropped the rpm a bit and the truck is very enjoyable to drive. I can hear the radio for the first time since 1994 . I might get a little less mileage running empty than with the 3. 73's, but I feel that it tows my fiver better with the 4. 10's.



Dean