2001.5 Axles, 3.54 vs 4.10 LSD

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First off, hello from a Newbie. I have just ordered my new truck (see signature) and the information I have gotten so far from your website has been a big help.

One problem that I had in getting my order accepted by the factory was with the axle ratios. I had wanted the 3. 54 with limited slip differential. A friend has this on his truck ('97 2500 5-spd) plus most of those posting on TDR seem to use this gearing.

What I got back from the dealer is that the factory is no longer making the 3. 54 with LSD (after June). I needed to choose between the 3. 54 without LSD or go the the 4. 10 to get LSD. Anybody else here about this?

I was originally upset about this. But after seeing quotes from DC about the 4. 10 getting better milage than the 3. 54 with the 24 valve engines, and the 24-v running most efficiently at 2200 to 2300 RPM, I begain to think that this was not a bad thing. When I calculate it out, with a 6-spd, 4. 10 and the 285/75-16 tires I plan to get I will be running at 72 MPH with 2200 RPM. Sounds good to me. I ordered the 4. 10 with LSD. By the way, I think the ideal ratio would be about a 3. 90.

What do you guys think? Still happy with your 3. 54 gears? Would you do the same if ordering yours today? Am I sick in the head?



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Wait'n for my 2001 2500QC, SB, 4x4, HO 6-sp, 4. 10 LSD, SLT++

 

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<font color=blue>Let me be the first to say :

<font size=+4>Welcome Aboard!</font>

<small>Please Enjoy your stay!</small>

Regarding the axle ratio it could be that that is all they are offering in the upcoming model years so they are changing the factories now. With LT265/75/16 I run 2250RPM at 75MPH. (auto, 4. 10 LSD). I don't tow anything at all and orginally got the 4. 10ratio based on the fact I am going to lift the truck and run 35 to 36" tires which will bring the ratio back done to roughly 3. 73 or so. This was going to be the first modification but I got "sucked" into BOMBing!! And now I can't go back!

Your top end speed won't be as high as a 3. 54 truck. I am happy with my 4. 10 ratio for now.

 

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I would have to say that you did the right thing. I ordered my truck two and half years ago with 3. 54 gears and I'm paying for it now. My tires are 3" taller than the stock tires and you can feel the loss of performance. I would like to switch to 4. 10, but I have a 4x4 and that can be costly.

Welcome to the TDR!

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98. 5 3500 QC 4x4
Driftwood/ Grey Int.
5 spd, 3. 54
PowerMax2, 19. 5" Alcoas, 245/70-19. 5 Michelins,
Ranchhand bumbers and toolbox, dual 3" with 5" tips, "Scotty Air System", Centerforce Dual Friction clutch, Autometer Gauges, Cobra CB, Sony CD player, Polk Audio Speakers, Upgraded fuel lines from tank to injector pump, Mag-Hytec Diff Cover, PacBrake.

69 Z-28 Camaro, Silver/Black, original motor, 58,000 miles

Building: 32 (Censored) 5 Window, "American Graffiti" replica

[This message has been edited by Jeff Clark (edited 06-15-2000). ]

 

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Hey, Ski Bum-
Unless you really plan on towing, I would go for the 3. 54's. I got the LSD and it is not that great. I find that I still spin the rear tires and that I have to put it in 4-wheel drive anyway. A friend of mine just spent $$$ to convert his 4. 10's over to 3. 54's due to top end and gas mileage.

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David Dressler
2001 Driftwood 3500 Quad Cab 4x4, 155 inch WB, 5. 9L HO Cummins Diesel (ETH), 6-Speed HD Manual (DEE), SLT+, 3. 54 Anti-Spin Axle, Camper Special Group, Trailer Tow Group, Leather, Sliding Rear Window, Jacob's E-Brake, Rhino Liner, VDO Vision (pyro, boost, engine oil temp. ), Weather Guard Diamond Plate Saddle Box, AND functional Halo light!
"Diesel, it's not just for breakfast!"

[This message has been edited by dresslered (edited 06-15-2000). ]

[This message has been edited by dresslered (edited 06-15-2000). ]

 

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I have 4. 10's and 34. 5 inch tires I am thinking of regearing to 4. 56's to regain my RPM's on the highway and hopefully bring back a little mileage, I lost 2-3 mpg after the tire swap no lift involved so I know it's not aerodynamics, I think the ISB does indeed like to rev. and yes folks I am calculating the old fashioned way and I do consider the tire height difference, I just think maybe if I regear, I could recuop some of the mileage loss, the cost of regearing isn't a factor I'm keeping tis truck 4EVER

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BLACK BEAST: 2K1 QC, SWB, Auto, 4X4, 4. 10 LSD, SLT, Black, Camel leather, Tow pckg, nv241HD, cab lights, 2 inch daystar coil spacers, 35 inch Mickey thompson claws, bushwacker flares, rhino lined bed and rocker panels.

soon to come; DD stage 1's, boost module, possibly van aaken.

GREEN MACHINE: 93 Jeep Wrangler 4. 0L, T-18, 38X11 Boggers, Dana 44's, AtlasII T-case, ARB's, warn and moser shafts, Ramsey 5K winch... . NEEDS A DIESEL!!!!!!

 

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Ski Bum,
Welcome!! As you can see there is different ways to look at it. My brother has a 3500 with 3:54's (5sp) with a cabover camper and pulls a 31' trailer with his and has never had any problems. It is still stock except for guages.

 

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I may be wrong but you should get the best mileage at the torque peak of any given engine. 2300 seems out of the torque peak. My own truck gets terrible mileage at those rpms,but could be from wind resistance. I seem to get best mileage at 1800 to 1900 with 3. 54 and 285 bfg tires. Also have 275 injectors power never is a problem. It may get better mileage at 1500 to 1600 I have never checked it as our interstate speed limit is 75. I think the DC engineer is a kook as this is my 3rd diesel dodge and they all got better mileage at 2000 or lower but all had 3. 54.

 

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Turbo I would bomb the injectors first. Best thing I ever did to my 24 valve.

 

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6bbl -

Where the heck are your driving? its 60 mph all the way from where I live (Millard) to downtown on I-80. #ad

 

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I agree 6bbl, the best milage is usually at the peak torque. But look at the 24-v torque curve, it has a flat mesa from about 1400 to 2600 RPM. What is really needed is a curve that shows engine efficiency versus RPM. Regarding you experienced MPG at different speeds: Assuming you're still in the same gear the lower RPM is going to give better milage because of reduced wind drag. If you change from 1800 to 2200 RPM in the same gear at highway speeds, the power to overcome the wind resistance has increased 49%. (1800/2200)^2=1. 49. The only way to really know if the engine is running more efficent would be to change gearing and run the same speed at different RPMs (so that the required power at the wheels remains the same) and check the change in MPG. Of course that's a lot easier said than done.

Originally posted by 6bbl:
I may be wrong but you should get the best mileage at the torque peak of any given engine. 2300 seems out of the torque peak. My own truck gets terrible mileage at those rpms,but could be from wind resistance. I seem to get best mileage at 1800 to 1900 with 3. 54 and 285 bfg tires. Also have 275 injectors power never is a problem. It may get better mileage at 1500 to 1600 I have never checked it as our interstate speed limit is 75. I think the DC engineer is a kook as this is my 3rd diesel dodge and they all got better mileage at 2000 or lower but all had 3. 54.

 

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Regarding my last post: Got the math wrong. That should have been (2200/1800)^2=1. 49. Where the ^2 means squared. The point being that the required power (due to wind resistance) increases with the square of the speed so that a lot of power is required for a small increase in speed. This was the logic used by Jimmy Carter during the oil embargo with the national 55 MPH speed limit. Reducing speed from 65 to 55 MPH uses 28% less energy (big difference). I course I kept driving 65 MPH or faster anyway.

 

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Ski Bum -

<font color=purple>You can "edit" your post. Simply click on the icon next to the date/time. Edit it and the resubmit it.
Its the icon in the middle for you.

If you edit it more then once, scroll to the bottom before you post and "delete" all the "Edited by . . " and when you post it will only display it once. Kinda just a housekeeping type thing.


[This message has been edited by KatDiesel (edited 06-15-2000). ]

 

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I may be all wet on this, but my understanding of the 4. 10 and the 3. 54 ratios is that each represents the number of engine revolutions for each revolution of the rear end. Therefore the 4. 10 has more lower end torque but it tends to sacrifice some high end speed. More rpm's mean more fuel use for the same speed and I would think this would translate to poorer fuel mileage, not better.

 

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Prowler 95-
You're close, the ratio is the number of driveshaft (not engine) revolutions per axle revolution. But lower RPM does not necessarly equal better MPG. Every engine is going to have a RPM where it produces the best power output per fuel input. Thats where you want to be running for best milage. What this RPM actually is, I don't know. But per some quotes from May Madness it seems the factory people are saying that it is at higher RPMs (2200) with the new 24 valve engines than was the case with the older engine models.

 

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another thing to consider is us auto guys have a . 69 OD vs a . 7? for the 5 and 6 speeds

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BLACK BEAST: 2K1 QC, SWB, Auto, 4X4, 4. 10 LSD, SLT, Black, Camel leather, Tow pckg, nv241HD, cab lights, 2 inch daystar coil spacers, 35 inch Mickey thompson claws, bushwacker flares, rhino lined bed and rocker panels.

soon to come; DD stage 1's, boost module, possibly van aaken.

GREEN MACHINE: 93 Jeep Wrangler 4. 0L, T-18, 38X11 Boggers, Dana 44's, AtlasII T-case, ARB's, warn and moser shafts, Ramsey 5K winch... . NEEDS A DIESEL!!!!!!

 

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I think that yes there's a majic rpm where your engine is more efficient. But, let's say for example that the magic rpm was 2,200 rpm. If, say, your stock gearing had you running at 1,800 rpm at 70 mph, and then you switched to different gears so that at 70 mph you'd be turning 2,200 rpm, I'd bet you wouldn't get better fuel mileage. Why? #ad


Because the amount of fuel blowing through the engine is proportional to the amount of air blowing through the engine. It may not be a linear relationship (because it may indeed be more efficient at 2,200 rpm) but it's still going to be more. More air, more fuel. #ad


I believe that with all things being equal (with unloaded trucks) you'd always get better fuel mileage with the 3. 54 gears. I'm glad I've got 'em. I turn about 2,080 rpm at 75 mph with stock size tires. With the same size tires I'd be turning approximately 330 rpm more (2,410 rpm), that's too much winding out for my tastes to do for extended periods of time. I've heard some people say they just get use to it. I doubt I would.

On the other hand, towing's a different story. I'd bet of 2 equal trucks, except one with 3. 54's and one with 4. 10's, there will be occasions where the 4. 10's would get better fuel mileage. As the towed weight increases the more possible it is for the 4. 10's to be more efficient than the 3. 54's. If I were planning to tow more than about 12,000 lbs. regularly, I'd take the 4. 10's cause I'd probably max out at only about 65 mph on level ground. I'd bet the 4. 10's would be more efficient with 12,000 lbs. on level ground (and up hill). #ad


The gear ratio is like Ski Bum said. 3. 54:1 means: 3. 54 driveshaft turns into the differential equals one full axle (and tire) rotation. 4. 10:1 means: 4. 10 driveshaft turns into the differential equals on full axle (and tire) rotation.

The . 69 of the auto OD compared to a . 7 manual will not give better fuel mileage because of the inherent reduced efficiency of an auto transmission.

I've said enough, WELCOME ABOARD! #ad


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Y2K 2500 Cummins ETC/DEE, SLT+, 4X4, Quad, LB, Intense Blue Sport, 3. 54 anti-spin, rear aux. springs (camper special), sliding rear window, all options except cab clearance lights including agate leather, totally stock, + a mpg increaser goodie

[This message has been edited by JyRO (edited 06-15-2000). ]

[This message has been edited by JyRO (edited 06-15-2000). ]

 

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i may be all wet here , but my 2000 , auto , 4x4 2500 with 3. 54 gear , and the factory lt 265's gets its best mileage reading , as looking at the trip computer when the engine rpm's are rght around 2000 rpm , plus or minus 100 rpm , even when driving around town if i forget to lock out od and i look at he computer when the engine is reving say 1400 - 1500 and i go out of OD into third and the rpm's jump up to about 2000 the trip computer jumps up 3 plus mpg. i have recently met a ram owner with a 2000 with 4. 10's , he gets horrible mileage , he is ready to have his truck switched to 3. 54 's . by the way anyone near mass with a lo mileage '99 or 2000 2500 4x4 wanting 4. 10's drop me a line , this guys truck only has 8000 miles and i'd bet he go for the swap.

edit ... when checking the computer on my way home , the mpg jumps initally my 3mpg , then settles out at 8 mpg higher , don't know about anyone else but my combo likes to run right at 1900 2000 rpm , which is 75 mph , and since the speed limit here is 55 - 65 mph , 10 over is all i dare ... usually ... #ad
#ad


[This message has been edited by Mopar-muscle (edited 06-16-2000). ]

 

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Ski Bum, didn't see in your post as to weather you planned on doing a lot of heavy towing or not, if your not then the 3. 55 gear is maybe fractionally better for freeway driving. If your truck feels good to you going down the rode thats all that counts. I've had both rear ends and liked them both but with my 99% empty driving the taller gear works for me. Regards Pete

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99'3500,quad cab,4X4,a/t
3:54,all the right packages!PROPER VALVEMENT

 

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From experience -

1988 - was going to by 4x4 but didn't like the ride. Bought 2WD. Kicked my own *ss for 5 years. Stuck it 10 times.

1993 - bought 4x4 and really wanted LSD. Didn't get LSD. Kicked my own *ss for 4 years. Stuck it 3 times.

1997 - bought 4x4, LSD, 3. 42 gears. Kicked my own *ss for 2 years. Spent $1,100 on 4. 10 gears. Wife kicked my *ss for 1 year.

2000 - bought 4x4 Diesel POWER, LSD, 4. 10 gears. Kicking Fiord & GMinie's *sses!! Wife still kicks my *ss!

Wouldn't do without the 4. 10's for anything!

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"Red Rage" - 2001 2500 SLT 4x4 QC Lowered Rear End 2. 5" 5spd, 4. 10 - 6900 miles and counting! 30' 5th Wheel

[This message has been edited by bennettj (edited 06-15-2000). ]

 

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Welcome aboard! About the ratios, I have a 3:55 with the 5 speed in my 98 and would not want the 4:10's Even towing I am fine. Empty I wish I had 3:08's. At 1600 rpm I get 23 mpg, at 2000 rpm I get 21 mph, i doubt it would go higher to run 2300 rpm!

The reason dodge may be having problems with the order may be most guys I know that have the LSD and 3:55's also have the 8800 lb option, which gives you the Dana 80 HB in the back.



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• 98 ISB,QC,5spd,2wd,3:54lsd.
• 2000 Terry 305G 5th wheel