6.4 hemi, 4.56 gears, speed and RPM's

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U&A

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Im going to re gear my 6.4 in the future and am guessing that 4.56's are what i should get but still in the beginning stages of research with this. I am running 35's and will not go any bigger than that. Currently with my 373 gears and 35" tires I have to do 80 mile an hour to be at 2000 RPM's.

What RPM's are you guys with 4.56's at when running at 60mph & 70 mph?

Also would like to hear from anyone with the 4:10's And the 4:88's if there is anyone with 4:88's.

Thank you
 

wyo2track

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Here's a little chart I made. I'm running 4.10's with 33's (275/70R18) stock size. I used a RPM calculator off of one of the gear sites I looked at. Your going to be approximately 150 rpm lower than these numbers with your 35's and 4.56's.


4th Gear, RPM's
R&P 60mph 65mph 70mph
4.10 2505 2713 2922
4.56 2786 3018 3250
4.88 2981 3230 3478

5thGear, RPM's
R&P 60mph 65mph 70mph
4.10 2054 2225 2396
4.56 2284 2475 2665
4.88 2445 2648 2852

6thGear, RPM's
R&P 60mph 65mph 70mph
4.10 1553 1682 1812
4.56 1727 1871 2015
4.88 1848 2002 2156
 
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U&A

U&A

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Here's a little chart I made. I'm running 4.10's with 33's (275/70R18) stock size. I used a RPM calculator off of one of the gear sites I looked at. Your going to be approximately 150 rpm lower than these numbers with your 35's and 4.56's.


4th Gear, RPM's
R&P 60mph 65mph 70mph
4.10 2505 2713 2922
4.56 2786 3018 3250
4.88 2981 3230 3478

5thGear, RPM's
R&P 60mph 65mph 70mph
4.10 2054 2225 2396
4.56 2284 2475 2665
4.88 2445 2648 2852

6thGear, RPM's
R&P 60mph 65mph 70mph
4.10 1553 1682 1812
4.56 1727 1871 2015
4.88 1848 2002 2156


This sir, is a VERY helpful post. Needs a sticky
 

Kingsize

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Very nice! Wish I could like this post 100 times. Very helpful for anyone doing this.

Here's a little chart I made. I'm running 4.10's with 33's (275/70R18) stock size. I used a RPM calculator off of one of the gear sites I looked at. Your going to be approximately 150 rpm lower than these numbers with your 35's and 4.56's.


4th Gear, RPM's
R&P 60mph 65mph 70mph
4.10 2505 2713 2922
4.56 2786 3018 3250
4.88 2981 3230 3478

5thGear, RPM's
R&P 60mph 65mph 70mph
4.10 2054 2225 2396
4.56 2284 2475 2665
4.88 2445 2648 2852

6thGear, RPM's
R&P 60mph 65mph 70mph
4.10 1553 1682 1812
4.56 1727 1871 2015
4.88 1848 2002 2156
 

SouthTexan

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The formula for rpm at a certain speed is

(Axle Ratio x Vehicle Speed x Transmission Ratio x 336.13) / Tire Diameter = RPM

Or you can just use a calculator on the internet like this one... RPM Calculator
 
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U&A

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Recommend brand of front and rear gear sets in a 4.56?
 

Kingsize

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Calculators are cool, but it's nice to see a chart that you can look at vs: looking at all those different combinations independently. I thank him for the time he spent putting it together.
 

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Hey guys have a 2016 ram with the 6.4 hemi 5.5 inch BDS 4 link lift on 37×12.5 on 20 inch rims and 3.73 gears. Going to swap to 4.56 gears. What you guys think. Just so dogish right now. Any input will be appreciated.
 
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U&A

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With tires that bug i would do 4:88. 4:56’s will help but you need all the help you can get with 37’s.
 

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Ok thanks just don't know 4.88 might be to much. What you think the rpm would be with then or the 4.56. Maybe 250 -500 difference. So many decisions lol
 

RoadRamblerNJ

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Here's a little chart I made. I'm running 4.10's with 33's (275/70R18) stock size. I used a RPM calculator off of one of the gear sites I looked at. Your going to be approximately 150 rpm lower than these numbers with your 35's and 4.56's.


4th Gear, RPM's
R&P 60mph 65mph 70mph
4.10 2505 2713 2922
4.56 2786 3018 3250
4.88 2981 3230 3478

5thGear, RPM's
R&P 60mph 65mph 70mph
4.10 2054 2225 2396
4.56 2284 2475 2665
4.88 2445 2648 2852

6thGear, RPM's
R&P 60mph 65mph 70mph
4.10 1553 1682 1812
4.56 1727 1871 2015
4.88 1848 2002 2156
I'm running same. 4.10s withh 33" mudders. 275/70r18. I agree with those charts. I run 90 miles every day and those #s are very accurate.

Not 1st, 2nd or 3rd? No Trophy!
 

mtofell

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When I was looking into bumping up to 4.56 from my 3.73 (stock tires) I seem to remember a rough estimate of the impact was to drive on the freeway in 5th instead of 6th. That put the RPMs right about where they'd be. The OD gears on this truck are so low that it's really not that noticeable. Even at 75+mph the noise and feel is really not much of a change.

I'm still thinking of re-gearing. The guys around here that have done it are all super happy.
 

RoadRamblerNJ

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Hey guys have a 2016 ram with the 6.4 hemi 5.5 inch BDS 4 link lift on 37×12.5 on 20 inch rims and 3.73 gears. Going to swap to 4.56 gears. What you guys think. Just so dogish right now. Any input will be appreciated.
What are you trying to improve the most? What type of driving? Hi-way or city? Looking for launching or mpg? Or, if you're just nuts like me, just buy the 4.88s or 5.11s if you can.

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RoadRamblerNJ

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When I was looking into bumping up to 4.56 from my 3.73 (stock tires) I seem to remember a rough estimate of the impact was to drive on the freeway in 5th instead of 6th. That put the RPMs right about where they'd be. The OD gears on this truck are so low that it's really not that noticeable. Even at 75+mph the noise and feel is really not much of a change.

I'm still thinking of re-gearing. The guys around here that have done it are all super happy.
Dropping into 5th only simulates what a taller gear might be like in that gear. You get no new info on launch, 1-2 shift, 2-3 shift, etc. My 2500 6.4 6spd has a 0.625 6th gear! Even 5th is overdriven. 4th is 1:1. Tall gears makes everybody smile!

Not 1st, 2nd or 3rd? No Trophy!
 

mtofell

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Dropping into 5th only simulates what a taller gear might be like in that gear. You get no new info on launch, 1-2 shift, 2-3 shift, etc. My 2500 6.4 6spd has a 0.625 6th gear! Even 5th is overdriven. 4th is 1:1. Tall gears makes everybody smile!

Not 1st, 2nd or 3rd? No Trophy!

Yeah, definitely all good points. I just always think the biggest annoyance of the re-gear would be the higher RPMs in top gear on the freeway. The reports I've read from guys who have done it rave about how much better it shifts and drives through 1-2-3, etc.
 

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Mostly hi-way back and forth to work every day driver. I'm just looking for the best compromise between power and mpg. Right now I'm getting about 10 mpg with the 3.73's running 93. But hey I'm driving a prius mpg is not at the top of my list. I tow also but mostly toys like 4 wheeler and side by sides
 
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U&A

U&A

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With 37’s and 4.88’s im prity confidante you will not be touching 2,000rpms at 70 mph. It will be close but that tall tire is what makes the difference. I would do 4:88 no question if i was running 37’s. These trucks are happy at 2,000 rpms on the highway. Im doing 4:56’s with my 35’s and no lift.
 

wyo2track

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I'm running same. 4.10s withh 33" mudders. 275/70r18. I agree with those charts. I run 90 miles every day and those #s are very accurate.

Not 1st, 2nd or 3rd? No Trophy!


LOL....No trophy..! Ok OK.. LOL..

I did make it....but its a FUGGIN' mess...LOL! I didn't find a way to import a nice looking chart that started at 20 mph and went to 80...LOL! In summary...2nd gear sucks!

To Brandon w/ the 37's; a swap to 4.56's may get you back close to your 3.73's stock tire size, but 4.88's would be much better. I don't think you'll see much of a mpg difference with that big of tire and lift with either gearing, but performance will be better.... So my vote is go big! 4.88's
 
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