Axle ratio

[damar]

according to Power Booster News "The 24 valve runs best at 1900 to 2300 rpm for fuel economy and 2400 to 3200 rpm for performance. With the 3. 54 axle at midrange of economy at 2100 rpm I am running 75. 4 mph. I don't like to tow my trailer that fast. Does anyone know if there is a 3. 73 ratio available for the Dana 70 rear end?? Also, can the computer be programmed to recognize the 3. 73 ratio to correct the speedometer?? A 3. 73 ratio would put me at 71. 6 mph at 2100 rpm. Also, the 3. 73 ratio would increase the pulling power slightly. That would be a help out here in the mountains. My truck is a 98. 5 stock with auto tx.

Thaks for the feedback. Dave

 

[HC]

There's information about someone who swapped to 3. 73's at http://earthroamer.com/main_truck/truck_differential.html
His truck has the Dana 80's in the rear, but if they have 3. 73's for the front 60 and the rear 80, then surely they can handle a 70.

My inclination would be to just drive your existing set-up at the lower end of the "economy" range. At 1950, you'd be doing ~70, and if you came to a hill and dropped out of OD you'd go to ~2800, which will sound bad but is actually right there in the performance band. I guess it all depends on how much it bothers you having to drop out of OD more often; but I would think running in 3rd up the hills would actually be really good for helping your transmission to live longer. I don't think people in general give enough credit to how much it reduces drivetrain stress (and increases transmission life) to drop into your "direct drive" gear (3rd for autos, 4th on the 5 speeds, 5th on the 6 speeds), especially when pulling loads or bucking the wind.

P. S. - I see your point, 3. 73 would be "perfect", wouldn't it? I'm just not sure that it would be so much better that it would be worth the $$$.

[This message has been edited by HC (edited 12-31-2000). ]

 

[Fireman Dave]

Right on, HC. I ordered the 3. 54 with my auto with the philosophy that I'd spend more time in 3rd when towing to preserve the transmission. Also, the 4. 10 would be a screamer at 75mph when in bobtail mode.

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2001 2500; SLT; 4x4; QC; LWB; Auto; 3. 54 LS; 265s; Camper; Tow; Sliding Rear Window; Travel Convenience Group; Cab Clearance Lamps; Forest Green

 

[Fred Swanson]

I'd seriously think about some transmission mods if your pulling in the mountains with the stock automatic.

There is a dramatic improvement with a VB and TC swap (like the one from DTT). More of that power will make it to the rear wheels, which you may feel is significant enough to keep the axle ratio right where it is.

The 3. 54 ratio is just about right, because you can drop out of overdrive, and still keep the motor in its sweet spot, and run at a decent speed. Plus the improved line pressures of the VB will keep the lockup engaged with less chance of slippage, which will hurt performance and shorten the transmission and TC life.

Plus the improvement in fuel mileage is a nice additive.

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Fred Swanson
Co-Owner
Canyon State Components, LLC
'00 QC,SB,4x4,Auto,3. 54 w/LSD,Trailer Package, Tow Package, DTT's VB & TC

 

[RKohn]

Tire changes can be an easier and cheaper way to change your effective ratio. Besides, you wanted to shed those factory skins anyway.

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Y2K Red Stealth Sport 2500 4X4 QC SLT+, 5-spd, 3. 54 anti-spin, 265-75-16 LTX’s (There ain’t no such thing as options, cause ya gotta have it all, including: DC’s dead cow/vinyl interior and don’t stop anti-lock brakes. ) Stock, but not for long. Oops, too late. What silencer ring? (More fun than my 98 SST)

 

[Barry]

FYI: The DANA 80 with the 3:54s can be changed to 3:73 or 3:90s with a R&P set that will slide in the existing carrier. The 4:10 is an animal all unto itself. I love my 4:10s when I am loaded and dislike them when empty. I checked into the 3:73 and 3:90 R&P sets and if I had the 3:54s I could have changed. Cost was $350 for the set. But since I had the 4:10s I would have had to change a whole bunch of stuff. Was not economially feasible. Swinging the bigger tires on the new trucks, DC really needs to offer us a bigger choice of ratios IMHO. I asked for a Gear Vendors for Christmas but no luck... ... ... .

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2001 2500 QC, ETH/DEE,4:10s, LSD, VA Magic Box, Boost/Pyro Guages, 4" Turbo back, BD Brake,Mag- Hytec Cover, Kleen Wheels, Energy Release, 70 gal. fuel, 20K Reese. 22,000 miles on 12/19/00 (RV Dealer)

 

[quadzilla]

I am curious about this, and have read the other posts in the past and commented on some of them regarding the different axle ratios and the theoretical fuel economy. I understand, somewhat, the concept behind the efficiency factors that go into figuring what engine speed is most efficient as far as burning fuel. What about drag on the vehicle? From what I remember reading in the TDR (issue 29 I believe) the differnces in the 3. 54 and the 4. 10 gearing as to efficiencies was almost negligible. Aren't we micromanaging a bit when we are splitting hairs on an item that is probably affected more by the weight of the stuff we are hauling in our toolbox or under the rear seat, my undetectable changes in throttle position without cruise on, by changes in wind speed and direction, by road surface condition, air pressure in tires, etc. than by the theoretical factors determined in a lab (I am guessing that is where they came up with these - I could be wrong).

In addition to the cost of installing new gears versus the alleged extra fuel consumption, what about the extra wear and tear at higher engine speeds. I am not talking about anything drastic. Just imagine all the extra revolutions over the life of the truck even 100 rpms would amount to. That is 6000 revolutions for every hour of drivetime. How about the extra noise.

Has anyone documented the efficiencies in real world driving? And if so, how can they say without a shadow of a doubt, that ALL conditions were exactly, I mean exactly, the same in order to have accurate results. Side by side comparisons? Are both trucks exactly the same? Exactly? I don't know. My fuel economy from one tank to the next is never quite the same, even if my driving has been as close to identical as I can make it for each tank.

These are just some thoughts. Personally, I have the 3. 54's and am satisfied with the mileage I am getting for the most part (around 17-18 in mixed driving).

I am not trying to come across the wrong way or rain on anyones parade here. Quite the opposite in fact. I don't know much about these great motors at all, and am trying to learn as much as I can from the people here on this site that do know. I am an engineer by trade, so can say this without fear of retaliatory comments. Some people take an engineering approach to some of these topics and over-analyze all the data without regard to whether or not it even makes a measurable difference in the least in real world application. Maybe there is a huge difference in fuel economy in the two gearings at any given engine speed. Maybe it is only at certain engine speeds. Maybe not at all. Who really knows. I don't know of a truly accurate way to test this in real world driving.

Any input? I DO appreciate all the info on this site, as it has helped me immensely in preventive maintenance on my '01 to ensure it will be around for a long time to enjoy, as well as all the tips on performance and economy as well as the fellowship that is evident on the site.

--Craig



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Name: Craig Clairmont
2001 Quad Cab 2500 4x4, Short Bed, ETC, Auto, 3. 54 gears, SLT Plus, Sport, Forest Green Pearl, Camper Special, Trailer Tow, 305/70R16 Cooper Discoverer AT tires on Stock Rims, Grizzly Double Bend Chrome Bars, Catch-All Front Floor Mats, Avital Remote Starter, APC Super White headlamps, Weather Tech Vent Visors, DC Mud Flaps, Turbo "unsilenced", K&N Filter in stock Airbox, Engine is all stock... for now. Line-X bedliner coming this fall...

Other Mopars:
1978 Ram 4x4 - 440, Convertible, Club Cab, Step Side Bed - Project Almost Done

1968 Plymouth GTX - 440, 4 Speed, Black Buckets, Console - Project Ready to Get Underway