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-   -   For the gear ratio gurus (http://www.jeepgarage.org/f73/for-the-gear-ratio-gurus-55890.html)

bill_de 03-05-2013 03:53 PM

For the gear ratio gurus
 
There has been a lot of talk that the eight speed will give the Hemi a little more pep off the line. With a lower first gear that makes sense. I just got my build sheet (Thanks Milous) and confirmed that the 5.7 now comes with a 3.09 rear in lieu of the 3.45.

Mathematically speaking, what is the net effect to the wheels of these two changes to the drive train?



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spyder873 03-05-2013 04:03 PM

Re: For the gear ratio gurus
 
3.09 is more of a open highway gear lower in torque but better when rolling on the highway, Lower Rpm at highway speed

the 3.45 would give you alittle more torque off the line but will cause higher RPM at highway speed

bill_de 03-05-2013 04:06 PM

Re: For the gear ratio gurus
 
Quote:

Originally Posted by spyder873 (Post 773670)
3.09 is more of a open highway gear lower in torque but better when rolling on the highway, Lower Rpm at highway speed

the 3.45 would give you alittle more torque off the line but will cause higher RPM at highway speed

"Mathematically Speaking"

You got the theory ... You left out the math.:lol:



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spyder873 03-05-2013 04:14 PM

I have never really been taught the math. A lot depends on your tranny gear ratios coming out the tranny as well.

I am sure I can find a formula for you some where. Lol

You would need a crawl ratio formula. With this formula you would be able to enter in any ratio from the tranny and diff. Combo

myoung84 03-05-2013 04:16 PM

Re: For the gear ratio gurus
 
I posted a big spreadsheet a while back that show the differences, mathematically speaking. ;)

http://www.jeepgarage.org/f73/compre...tor-55409.html

bill_de 03-05-2013 04:20 PM

Re: For the gear ratio gurus
 
Quote:

Originally Posted by spyder873 (Post 773684)
I have never really been taught the math. A lot depends on your tranny gear ratios coming out the tranny as well.

That's why I asked about the net effect of the two changes to the drive train, meaning rear and tyranny. It's also why the title says, for the gear ratio gurus.

Hell, if it was easy, I could figure it myself. :lol:

I am wondering if the perceived improvement is a case of mind over math. :)



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ColdCase 03-05-2013 04:36 PM

Re: For the gear ratio gurus
 
2011-2013 Axle ratios:
3.45:1 - 3.0L
3.07:1 - 3.6L
3.45:1 - 5.7L
3.70:1 - 6.4L

For '14:
3.45 for V6 and EcoDiesel; 3.09 for V8.

The 8 speed has a granny of a first gear 4.714 then 3.143 - 2.106 - 1.667 - 1.285 - direct - 0.839 - 0.667. The older V6 5 speed had a 3.59 first where the older V8 6 speed had a 3.00 first.

Doing the math for Overall first gear (axle and transmission combined):
Old 10.98 V6,10.41 5.7L V8
New 16.26 V6, 14.57 V8 So you should see better acceleration from a stop, torque control limited however..

Doing the math for Overall top gear:
Old 2.54 V6, 2.32 5.7L V8
New 2.30 V6, 2.06 V8 So your engine will be turing over at less RPMs while cruising at 75 mph.... good for economy not as good for performance.. but you can always manually select a lower gear for better performance.

spyder873 03-05-2013 05:01 PM

Re: For the gear ratio gurus
 
here is a crawl ratio calculator where you will be able to enter in all the gear ratios and get the finial gear ratio for each gear

Gear Ratio Calculator

here is a little better one that explains it more

http://www.marlincrawler.com/java/getratio.html

bill_de 03-05-2013 05:04 PM

Re: For the gear ratio gurus
 
Thanks everybody!



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canis 03-05-2013 08:10 PM

Re: For the gear ratio gurus
 
Did the stall speed change with the lower gears though?


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