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Anyone here running 3.90:1 rear gears..

1797 Views 6 Replies 6 Participants Last post by  The Hog
I was just wondering what switching from 3.73:1 to 3.90:1 rear gears would do for 1/4 mile time. Say a stock "V" is 13.4 in the 1/4 mile. What would it be after switching to 3.90:1 rear gears. The way i see things now... 6th gear is useless, perhaps switching to 3.90:1's will wake it up! :)

BTW.. what would the cost be for the gears and installation.
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I've often wondered this myself. I'm not aware of a single person that's switched their stock rear gear ratio, so I'll be interested to see if anything turns up.

How 'bout it, Florian- Did Doug throw a 4.11 in that diff for you? :D
I feel like putting any aftermarket gears in these cars will dramatically weaken the rear end. I may be wrong, but just from experience with F-Bodies, it seems this would still hold true. In my experience on the forums as well as personal experience, it seems that people who had the stock 10 bolts in f-bodies seemed to usually be alright. It was when they started changing out gears that rears started whining and breaking. Unless they're set up exactly right with the backlash and everything, they will be weaker than stock. Although there are many trans shops as well as GM LS-series shops out there, I think many are not able to install gears exactly correct. Even when I bought my assembled 12 bolt straight from Moser for my T/A, it still whined on the highway. I don't know if I would risk it in these cars, although 4.11s would be nice :D
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I had a 2005 Mazda RX-8 (Rotary engine) that made a whopping 152 ft/lbs of torque. That thing came factory with a Carbon Fiber Driveshaft an 4.44 gear :eek:.

Now that would be fun.....:devil:
If I'm not mistaken, Parker's Madman diff has a 3.90 ratio.
There are no other gear ratios available for the factory differential, not unless something very new is out there, no demand therefore no investment in the parts and machining.

I left Florians car at the 3:70 ratio, hes adding plenty of power, so he wont need to compensate.

A drag application, I recommend a 4:10, but thats only if the maximum 60ft is critical for you.

I can offer any gear ratio from a 3:08 to a 4:56 on My Traction Package.
There is almost no difference between a 370 and 390 ratio, the swap is going to be just north of pointless. If you want to go faster in the quarter put your money where it will do you some good, nitrous, maggie, drag radials, etc.
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