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Discussion Starter #1
has anyone gone from 3.55 gears to 3.92, if so how much of a diffrence did it make. i cant pratically go to 4.10 because i drive highway everysingle day. 1/4 mile diffrence and how did it all feel? is it worth it?
 

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I like trucks
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I hear its a night and day diffrence. But for the money it makes sense to just go to the 4.10's. Im going from 3.55 to 4.56. But I have 32's so itl lower that a lil bit. Your highway rpm's between 3.92 and 4.10's isnt that much. But good luck either way :biggthump
 

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I agree with TJ, just go right to 4.10's if you're thinking about 3.92's. There won't be that much of a difference in highway RPM's, but should be a bit of a difference in low-end power.
 

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ive done it. i like it. not too harsh on the highay either. netted a 20mpg cruise when i went to southwest pa to pick up my motor, got like 19 on the way home :banana2: :drive:
 

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Discussion Starter #5
and you would say u like it alot, definatly noticable acceleration, im really skeptical of some things and i just want to make sure this is what i want god knows i have no money so i gotta spend it on the right stuff. thanks for yalls help the 4.10s dont sound like a bad idea either guess ill jus have to think about it. i hate being poor :cussing:
 

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Discussion Starter #6
ive been reading up, gettin 4.10 gears will kill top speed wont it? and if i daily drive my truck will my gas mileadge be much more affected from 3.92 then the 4.10s. im really close to doing this but i only want to do it once. o and another question, will new gears help throughout the speedometer, like, will going from 60-100 be faster or slower. im so confused could someone please lay all the information out. everything you know about increases and stuff because no forum anywhere actually lays it out for me! thanks for the help...geez :confused:
 

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I have the 3.92 in my truck and they are nice, i am getting around 20mpg with my 3.7 auto.
 

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Discussion Starter #8
i really just want someone who switched from 3 55 to 3 92 to say something like......"damn it helped my truck so much, god it was so worth the money"...can anyone say that???
 

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Ace said:
i really just want someone who switched from 3 55 to 3 92 to say something like......"damn it helped my truck so much, god it was so worth the money"...can anyone say that???
I don't think you'll find many people to say that. If most people did the switch, they went right to 4.10's. I'd seach around to see who went to 4.10's instead, because if it were me, I wouldn't do 3.92's.
 

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yeah my truck came stock with 3.92's, but i wold never switch to them, if i were doing a grar swap, it would be 4.10's. the 3.92's are damn nice, but to go from 3.55's to 3.92's you are not going to see as big of a change as you want.
 

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Discussion Starter #11
i drive on the highways alot though, dont people say if u travel highway those gears will kill ur mileage, O SO CONFUSED
 

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Ace,

Here are some numbers to ponder:

Going from 3.55 gears to 4.10s, is a 15.5% change.
If you're now turning 2500 at 70 mph your rpm would increase to about 2890 rpm.

Going from 3.55 to 3.92 gears is a change of about 10.4%. You'll go from 2500 to 2760 rpm.

Not a heckuva lot of difference in rpm between the two gear-sets (about 4.5%), which is what can affect your mileage.

I don't know how fast you drive on the highway, or what rpm you're used to at cruising speed, but now you can figure out how much your rpm would increase with either ratio.

One reason for going with the "lower" 4.10 gears is it gives you more flexibility to go with "taller" tires. Any increase in tire diameter will decrease your engine rpm at a given speed, just as though you were going to "higher" gear ratios. That's why when people put on bigger tires they are often disappointed when they lose so much acceleration. Not only do the tires weigh more, they effectively change the final drive ratio.

I think the 3.9 engine likes to rev, and by observation I don't see much mileage change between say 60 and 70 mph (a 17% change in rpm!), as long as I set the cruise or drive at a steady pace. You might notice a difference in your mileage going from 3.55 to EITHER 3.92 or 4.10, but you probably wouldn't notice much difference between the two. Most people are recommending to go with the gusto and use the 4.10 gears. And if you want to "fine tune" that, you can go with taller tires. Seems like a reasonable choice to me.

(Your mileage may vary based on road conditions and how you drive) :D

BTW, if you want to "kid yourself" about gas mileage, just leave the speedometer alone after going to the 4.10's and it'll give you a false reading that'll inflate your mileage figures nicely. :biggthump
 

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Dodgerjack said:
BTW, if you want to "kid yourself" about gas mileage, just leave the speedometer alone after going to the 4.10's and it'll give you a false reading that'll inflate your mileage figures nicely. :biggthump

That's not true. Then GenIIIs get the speed off the diff of maybe the ring gear? Not sure on where, but the ONLY thing that'll knock the speedo off on a GenIII is new tires. I have a friend with 4.56s in his R/T and his speedo is accurate.


To add my $.02 to this. I'm not sure of your motor but as long as you aren't doing 90 on the interstate your mpg shouldn't suffer too much. If it's a V6 I seem to get the same mileage whether on the highway or on the interstate (10 mph difference here) so that's a good comparison to look at, and in many cases, the truck will be in the powerband already so mpg might actually get better. But if you really want the power difference, go for it.

You'll feel the power off the line everytime.
 

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Discussion Starter #14
thanks a million for the help guys, yall sold me to the 4.10s, if it gets bad i can find other ways to get places lol....jus outta curiosity does anyone know if top speed decreses, thanks again :yourock:
 

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Discussion Starter #16
ahhh thanks im excited someone noticed!!!!!
 

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92dakotahd said:
That's not true. Then GenIIIs get the speed off the diff of maybe the ring gear? Not sure on where, but the ONLY thing that'll knock the speedo off on a GenIII is new tires. I have a friend with 4.56s in his R/T and his speedo is accurate.
That's interesting. I wonder where the sensor could be located on the differential? The pinion gear would have be turning faster for any given wheel rotation speed, so it would have to sense the ring gear or axle rotation speed. Axle rotation differs on either side when cornering, so I doubt they use that. I would think it would have to be an electronic sensor and sending unit, because they wouldn't run a speedo cable from way back there. My manual only covers through '96. Anyone know how this works?
 

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Discussion Starter #20
thanks guys, i had a decent bday night but now i feel like imabout to throw up i think im dehidrated idk i feel like crap, and i didnt drink, but i have a few stories about 2day ill post tom, lata
 
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