Re Gearing

highoctane

highoctane

Caught the Bug
jnabird333 said:
Seriously??? Are you trying to blow their motor? Even if the engine could stay in overdrive (which I doubt with the 3.8L gutless wonder) that would be 2650ish RPM @ 70MPH (which most consider pretty slow). Edit to add: Should a downshift happen on the interstate the engine would be close to the red line due to the large gear change from OD that you mentioned.
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My '08 with 5.13 gears and 37s was higher than that 2650 rpm. Hell even my '08 Rubi when it was stock with a 6 speed and 4.10 gears wasn't far off from 2650 rpm at 70 mph. You certainly won't "blow your motor". That down shift wouldn't be much different from dropping from 6th to 5th for a pass or hill, since that is a 1:1 ratio in both transmissions. You'd be at about 3800-3900 rpm with 5.38 gears and 3rd gear in the auto on 33s. Is it optimal? Probably not for a dd, but it'll work great if you can deal with the rpm, and live in a not so flat area.
 
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JKCRWLR

JKCRWLR

New member
I just added 5.13's and run 37's. Adam's Driveline convinced me on this choice and I couldn't be happier. [emoji41]
 
Pyro1415

Pyro1415

New member
Lol you guys at like 2600 rpm is too much for the 3.8... Every time the wind blows and it pops out of over drive it's at over 3 to 4K. I've even shut my od off for hours on the interstate so I could stay at speed. Final thought the 3.8 is made to breath a little and can use the extra rotations.
 
ITLL GO

ITLL GO

New member
Crap. Just found out I have 3.73 with my auto 3.6. I just thought it was 4.10. That's prob why it feels more sluggish then others keep telling me. Thanks for whom ever posted the Vin look up link. Gunna def replace with 4.88 now
 
flectarn

flectarn

New member
MR.Ty said:
4.88

And don't forget a programmer if you have an auto
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A little late to the party, but what role does the programmer play in this scenario? Just tells the computer it's working with a different gear ratio to make the proper adjustments?
 
highoctane

highoctane

Caught the Bug
flectarn said:
A little late to the party, but what role does the programmer play in this scenario? Just tells the computer it's working with a different gear ratio to make the proper adjustments?
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The '12 and up JK will go into a limp mode if the axle ratio that is programmed in the pcm does not match what is actually installed in the vehicle.
 
MR.Ty

MR.Ty

Token East Coast Guy
flectarn said:
A little late to the party, but what role does the programmer play in this scenario? Just tells the computer it's working with a different gear ratio to make the proper adjustments?
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Yes. If you have an automatic it will adjust the shift points to compensate for the new gear ratio. As other have said, the Jeep will go into limp mode if not.
 
Jk4lfe

Jk4lfe

New member
I just put 5.13s in on 35, at 70 mph im running at 2200 ish rpms and its a breeze on the 3.8L oh yeah its an automatic!
 
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