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Old 04-21-2020, 11:15 PM   #1
dadsz28's Avatar
Drives: 5th gen pending
Join Date: Jun 2018
Location: south jersey
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Et difference with 3.91s

Hey guys I am on the fence on doing 3.91 gears on my cammed and stalled Camaro car runs mid 11s. Can anyone give me what kind of improvement in ET they have gained. From what I gathered around .2 tenths?
Figured I would ask for anyone who has done it thanx.
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Old 04-22-2020, 08:27 PM   #2
Joe M 2012 2SS

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Location: Shelby NC
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.150 gain in the 1/8th mile. No 1/4 mile track near where I live. Car runs 7.1-7.3 in the 1/8th depending on prep/DA.

I ended up having to remove the first set I put in, Motive. Too much gear whine. Many others have experienced the same regardless of how well they are installed.

Went with AAM and they were originally quiet. Developed a slight gear whine over time, but much less than Motive.

I'd highly recommend swapping out the factory clutch pack differential with an Eaton True-Trac when you do the gear swap.

It will still depend on which cam/stall you have as to what rear end gear will work best. 391's do work for a wide variety.

Shift points will need adjustments, as well as speedo.

Roto-Fab intake, SW 1 7/8" LT w/hi flow cats, Flowmaster outlaw exhaust, UDP, 160* stat, Circle D 3200, Moroso catch can, TCI line lock, Zex Nitrous 125 shot, 3.91 gear, Eaton True-trac, DSS 1000hp axles.
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Old 04-23-2020, 08:11 AM   #3

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I saw a solid .15 gain going to 3.91s on a H/C setup 2mph gain
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Old 06-06-2020, 01:53 AM   #4

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Drives: 2013 Camaro SS
Join Date: Feb 2017
Location: Indiana
Posts: 798
Originally Posted by 62nalide View Post
I saw a solid .15 gain going to 3.91s on a H/C setup 2mph gain
I thought mph would drop with 3.91s?
2013 Camaro SS
Kooks Headers Vararam DRX 1le Differential 3.91
Bo White throttle body Magnaflow Competition Exhaust
12.391 112 MPH 10/05/19
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