Anyone convert a 3.21 to 3.92?

[thomasr7]

I am also looking at possibly changing my gear ratio. I have the 3.21 with the hemi listed in the attachment and would want to change to 3.92 for more towing. I talked to the dealer today and they indicated they would have someone call me back on monday with info. Will be interesting to see what they say. I love my current truck and would happily spend a few thousand to change it over instead of buying a 2500 if it is possible.

 

[silver billet]

@thomasr7 I'd advise you not to do this. It's going to cost you a lot of money and in the end it will only give you more power off the line from a dead stop.

Where are you feeling a lack of power? What speed? I'm willing to bet that anybody who feels the 3.21 is "not powerful enough" and then goes through this gear swap to a 3.92, will not feel they got their money out of it; it will still feel "not powerful enough".

Don't be fooled by the 3000 pound towing rating difference. It's a difference on a paper, or when drag racing a trailer from stoplight to stoplight. In the real world when you're towing, they will not feel any different when accelerating down an on-ramp, merging onto the freeway, passing trucks up a hill etc, they will be 100% identical. You will only notice a difference when accelerating from a dead stop, and then I ask you: how often/long do you spend in first gear? Because when I'm towing, my truck spends seconds in first gear, and it has literally the least amount of trouble in first gear. It has the most "trouble" (that's the wrong word, I don't feel underpowered) on the freeway, but again, no difference there for gear ratios (your transmission will downshift, that's what its there for).

 

[ferraiolo1]

I am also looking at possibly changing my gear ratio. I have the 3.21 with the hemi listed in the attachment and would want to change to 3.92 for more towing. I talked to the dealer today and they indicated they would have someone call me back on monday with info. Will be interesting to see what they say. I love my current truck and would happily spend a few thousand to change it over instead of buying a 2500 if it is possible.

You will need a new front diff assembly. And it doesn’t change your legal towing rating. By the time you pay for everything you could just buy a different truck


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[AV8OR]

I wish someone would do a YouTube video of the two axle ratios side by side 3.21 & 3.92:

(1) Drag racing 1/4 mile

(2) The Ike Gauntlet extreme tow test with a 5000 pound loaded trailer

(3) Long range 500 mile fuel comparison pulling a 5000 pound trailer

(4) Long range 500 mile fuel comparison no trailer

Both for the Hemi and the EcoDiesel

 

[silver billet]

I wish someone would do a YouTube video of the two axle ratios side by side 3.21 & 3.92:

(1) Drag racing 1/4 mile

(2) The Ike Gauntlet extreme tow test with a 5000 pound loaded trailer

(3) Long range 500 mile fuel comparison pulling a 5000 pound trailer

(4) Long range 500 mile fuel comparison no trailer

Both for the Hemi and the EcoDiesel

If you have two pedal bikes, one is a 9 speed and the other an 18 speed, both bikes are in different gears, but both bike riders are pedaling just as fast and both bikes are moving just as fast.... does it matter if the one bike is in "gear 9" and the other is in "gear 18"? Would you think one of those bikes would have more trouble than the other one maintaining speed simply because the gear number is different? Or would you instead see that since both bike riders are pedaling just as fast and the bikes are moving just as fast, the same amount of force/work is being done in both cases and neither has an advantage despite being in a different gear (number)?

You don't need to compare 3.21 vs 3.92 up the ike because we can prove (mathematically) that they will be virtually identical experiences.

As for the ED vs hemi, that has been done already. The Hemi is still stronger though it obviously revs much higher while doing it.

 

[ksn240]

If you have two pedal bikes, one is a 9 speed and the other an 18 speed, both bikes are in different gears, but both bike riders are pedaling just as fast and both bikes are moving just as fast.... does it matter if the one bike is in "gear 9" and the other is in "gear 18"? Would you think one of those bikes would have more trouble than the other one maintaining speed simply because the gear number is different? Or would you instead see that since both bike riders are pedaling just as fast and the bikes are moving just as fast, the same amount of force/work is being done in both cases and neither has an advantage despite being in a different gear (number)?

You don't need to compare 3.21 vs 3.92 up the ike because we can prove (mathematically) that they will be virtually identical experiences.

As for the ED vs hemi, that has been done already. The Hemi is still stronger though it obviously revs much higher while doing it.

The biggest difference is if you’re going to increase tire size. I run 35s on 3.21 gears and it is just fine but 3.92s would be much better. I shift in and out of 8th gear routinely. I really want to run 37s but would not work too well with 3.21s and I would likely lose 7th gear the majority of the time.

 

[silver billet]

The biggest difference is if you’re going to increase tire size. I run 35s on 3.21 gears and it is just fine but 3.92s would be much better. I shift in and out of 8th gear routinely. I really want to run 37s but would not work too well with 3.21s and I would likely lose 7th gear the majority of the time.

Agreed, bigger tires and/or offroading change the story completely.

 

[Jake103]

If you have any thoughts of towing heavy or lifting and going with a 34"+ tire without a doubt 3.92's. Take off will be much better and crusing will be a lot better not as much shifting. Otherwise if you are going to keep it stock and only tow once In A while 3.21's will be fine, most guys go with the 3.92's just because they like the initial take off better and you can tow a little easier. Those 8 speeds really help both, unlike an old 4 speed, gears did matter more.

 

[Neurobit]

You will need a new front diff assembly. And it doesn’t change your legal towing rating. By the time you pay for everything you could just buy a different truck


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^^^This^^^

 

[TXRAM632]

I have a 21 Laramie with 3.92 gears and am interested in swapping with someone that has the 3.21. My fuel mileage is just horrible with the 3.92 and I don’t really care about the towing capacity. I am in north east texas if anyone is interested in a swap.

 

[ferraiolo1]

It’s not going to change enough to justify the time and effort to swap just for a little gain in mpg.


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[TXRAM632]

Well maybe not but driving from texas to ok. I do good to average 16-16.5 mpg. I have to believe the 3.21 would help. If I can’t get better I may have to go to a Chevy diesel

 

[brian42]

Are you driving that route a lot? Are you cruising over 70 mph?

Driving habits, environmental conditions, and truck weight have just as much to do with it. If you wanted maximum fuel economy then a 2WD Tradesman is what you want. V-8, 4x4, ORG, tech packages, etc., all add weight to the truck. They don't seem like much individually but it adds up and you have to decide how much comfort/convenience you want at the sacrifice of economy.

The longer the list on the window sticker the less chance you have of seeing those MPG numbers posted on it. A Laramie already has a base package with included comfort and tech options that add weight. If you've done anything else to the truck since you bought it (lift, oversize/E-rated tired, etc.) those are also economy killers.

There's plenty of 3.21 vs 3.92 threads around and if this was 4-speed I'd say go for the swap. Since we're talking 8-speed there's very little to gain, especially for what it's going to cost. It would take a long time for you to come out ahead at the pump in that deal.

I read of guys with 3.92s getting better mileage than me (and I have 3.21s). Too many variables for me to feel like I got the short end of the stick.

I didn't buy an all-motor V-8 for the fuel economy. It's not like I don't care (10 MPG would make me a little peeved) but I certainly didn't expect the window sticker (17 MPG overall on mine). My expectation was 15 mpg (which is what I got in my last truck...F-250 diesel) and that's right about where I'm at. Good enough for me since I've got a long list on my window sticker.

 

[90Addict]

I'm in Delaware and am very interested in a swap. I have 3.21 gears and need the 3.97 for the 35s I run. Anyone semi close?