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Dakota Performance
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Murray
Dodge Dakota
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7/10/2007
21:42:48

Subject: 3.91 gears
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I have 03 Dakota with a 4.7 and an automatic transmission, it has 3.55 gears and an open differential. I have a LSD to go in it and a 3.91 ring and pinion. I know I want the LSD in it for sure but I'm having second thoughts about the gear. I want to know if anybody has this set up and likes it. The tire size is 255/65-16.



modain
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7/10/2007
21:53:21

RE: 3.91 gears
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If you're waivering on the 3.92 gear change because of fuel economy concerns, make the change. Everyone who has swapped from the 3.55 gears to 3.92 or even 4.10 (with large tires) have reported an increase in MPG. This is mostly due to the tires are easier for the engine to rotate.

I have 3.92s in my QC and 3.55s in my Durango. I can't wait until I get off my wallet to change the Durango's gears. Better acceleration and MPG - what's not to like?

What's your left foot doing?
==============
2002 Graphite QC SLT Plus, 4.7L, NV3500, Superchips 3715, 3.92 LSD, R/T rear swaybar, no chrome, loads o'fun...
2001 Patriot Blue Durango SLT, 4.7L, 45RFE, Superchips 3715, 3.55 Open (for now)
1999 Forest Green Dakota RC Sport, 2.5L, NV1500, 3.55 Open



Murray
Dodge Dakota
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7/10/2007
22:13:31

RE: 3.91 gears
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Sounds good, I was also worried about traction problems in the rain. It has some problems now with the stock rearend. It also may be because of the open rearend.



Careful
Dodge Dakota
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7/11/2007
00:02:25

RE: 3.91 gears
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Just be careful in the rain or it will get away from you.



Bob Lincoln
Dodge Dakota
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7/11/2007
08:38:53

RE: 3.91 gears
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"Everyone who has swapped from the 3.55 gears to 3.92 or even 4.10 (with large tires) have reported an increase in MPG. This is mostly due to the tires are easier for the engine to rotate." This defies all logic. The engine will be turning at higher RPMs and will give more power, but worse gas mileage. I just got 22.3, 21.1 and 25.1 mpg in three tankfuls on a long trip - stock V6 Dakota 4x4 club cab. You will NOT beat that with 3.91 gears.



Well
Dodge Dakota
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7/11/2007
12:14:14

RE: 3.91 gears
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Well, actually probably if you had a 5-speed with an overdrive you would.



Kowalski
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7/11/2007
16:00:46

RE: 3.91 gears
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No one is saying this will give a 4.7 better milage than a v6, not sure how anyone got that idea. I went from 3.55 to 4.10 limited slip with my 4.7, and saw a small mpg inrease (from 15 to almost 16). Power is up substantially, and it launches great on dry pavement. I know it seems counter intuitive, I was skeptical of those claims myself until I tried it. I don't believe it has anything to do with the tires being easier to turn though; I believe the 4.7 may just be a little more efficient turning more revs - all motors make their power more efficiently at certain rpms. The relationship doesn't have to be linear between power, efficiency, and rpm. We haven't seen this claim for any of the other engines.

Lead, follow, or get out of the way

TexasTodd
Dodge Dakota
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7/12/2007
22:55:48

RE: 3.91 gears
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What he said



EATPOOP
Dodge Dakota
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7/14/2007
22:49:47

RE: 3.91 gears
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I WENT WITH 4.10 GEARS AND 32" TIRES AND GET 18-20 M.P.G.



Pugs
Dodge Dakota
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7/23/2007
12:15:27

RE: 3.91 gears
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I do a lot of highway driving, cruising at about 70 mph. I don't see how 3.92 would improve mileage. I do see a benefit of mpg increase in city driving though as the power band issue described above. But all things equal at crusing speeds on the highway, no way 3.92 will show improved MPG over 3.55. I have a 4.7 5 speed with 3.55 gears and ususally get 22-23 MPG on the highway - only a K&N Drop in filter, rest stock.



Shoe
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7/24/2007
12:54:58

RE: 3.91 gears
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I got 20mpg in mine on the way back from Texas going around 70-75mph and I do not have cruise (long story). I got on it a bunch of times. I bet you if I babied it I would have got 21-22mpg. Not much of a difference.

Finally... a V8. '01 Dodge Dakota RC, 4.7, 5-speed, 3.92 LSD. = R/T Killer.
well at least a stock one

Pugs
Dodge Dakota
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7/24/2007
13:00:34

RE: 3.91 gears
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Two advantages:
1) you have a reg. cab....lot less weight.
2) Texas is a lot hotter then Ontario!! Our trucks get wayyyy better milleage in the heat...I get around 100 KM more to a tank in the hot mid-summer months, then in cooler weather.



DMACDAK
Dodge Dakota
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7/24/2007
16:05:06

RE: 3.91 gears
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I have an 03 4x4 cc 4.7 5 spd manual with 33 inch tires and switched from 3.55 to 4.10 gears. I also saw a mpg increase after the swap. This weekend I drove about 600 miles and got an average of 20.86 mpg cruising at 75-80 mph, the same trip with the 3.55 gears I would get 19.xx mpg. I think kowalski is right about the 4.7 being more efficient in the higher rpms.



Pugs
Dodge Dakota
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7/24/2007
16:36:25

RE: 3.91 gears
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The stock tire size is around 29" (2wd that is), so you switching to 33" tall tires and re-gearing to 4.10 effectively doesn't change anything. In effect you running 4.10 gears with 33" tires is marginally different (3.59)then running the stock 29" with 3.55 gears. That's why you're getting the good MPG.
If you were running the 33" tires with the 3.55 gears, it would be like having a stock tire size with 3.11 gear set...way too low for our trucks! That's prolly why you only got the ~19, then saw the benefit when lowering the gear set.
I like the 3.55's, I don't tow, and do freeway driving. If I towed more and did a lot of stop and go city driving, I'd see a benefit of changing to a 3.92.



Shoe
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7/25/2007
00:52:15

RE: 3.91 gears
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Um... I thought you made more power in cooler air? More power means more efficient. I could be wrong though. Oh and 3.11 gears are not low gears, they are high gears.

Finally... a V8. '01 Dodge Dakota RC, 4.7, 5-speed, 3.92 LSD. = R/T Killer.
well at least a stock one

Pugs
Dodge Dakota
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7/25/2007
06:53:16

RE: 3.91 gears
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Yup...right, you do make more power in cooler air. But more power = more gas! Cooler air has more O2 and I believe you need more gas - something along those lines.
Yes...my typo above, 3.11 is too high! Would have no guts.



Pugs
Dodge Dakota
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7/25/2007
09:48:37

RE: 3.91 gears
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Also forgot...Shoe...your truck looks to be lowered quite a bit. Lower would mean less wind drag under the truck at high speeds also giving better mileage.



Shoe
GenIII
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7/25/2007
13:39:13

RE: 3.91 gears
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Nope, not lowered. That is a picture of my previous truck that I had. Yes, it would have more 02 because the air would be more dense so you would have more molecules of it over a given area, but your motor would compensate for it with more gas. Yes, this means you are using more gas, but if you do not have to get in the throttle more I would assume that you would not lose any power. Just look at CAI, they do help on horsepower and MPG.

Finally... a V8. '01 Dodge Dakota RC, 4.7, 5-speed, 3.92 LSD. = R/T Killer.
well at least a stock one

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