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3.73 or 3.90?

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Old Sep 14, 2011 | 09:47 PM
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Default 3.73 or 3.90?

My 4.10's are on their way out, it's time to replace my gears.

I have 315 Nittos in the back and they won't hold 1st or 2nd gear at all. If I replace with 4.10's and add stickier tires, I'll probably just blow my 10 bolt out of the water. Solution is to lower the gear ratio. So now, 3.73 or 3.90? What do ya'll say?

I feel like I'd lose a fair amount of acceleration with 3.73's, but most likely get all of the power to the ground. What about 3.90's?

(6speed car)

Last edited by nik1703; Sep 14, 2011 at 10:22 PM.
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Old Sep 14, 2011 | 10:09 PM
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Matters transmission, power, power adders ect.
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Old Sep 14, 2011 | 10:15 PM
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Originally Posted by 89pigeontoe
Matters transmission, power, power adders ect.

What?

I have a stock T56. Everything else is in the sig.
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Old Sep 14, 2011 | 10:57 PM
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Tough call. The T56 is nice with that 6th gear. I have stock gears, but if I was going to move up numerically I would probably go with 3.73's, but my car just has a few bolt ons. And I like my 29mpg on the interstate.
Is your car a DD or just a weekend toy or what? That would probably be the biggest question to ask.
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Old Sep 14, 2011 | 11:16 PM
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3.90s
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Old Sep 14, 2011 | 11:32 PM
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I have a 3.70, & think that a 3.90 would have been more appropriate because the LS engine 'comes on' at higher RPMs.
You can always shift to one of the OD speeds for cruising.
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Old Sep 14, 2011 | 11:50 PM
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I'm debating 3.90's or 4.10's myself. In to see what some opinions are.

"Matters transmission, power, power adders ect."

Right on brother, right on.
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Old Sep 15, 2011 | 12:28 AM
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Originally Posted by LS1WS6dreamer
Tough call. The T56 is nice with that 6th gear. I have stock gears, but if I was going to move up numerically I would probably go with 3.73's, but my car just has a few bolt ons. And I like my 29mpg on the interstate.
Is your car a DD or just a weekend toy or what? That would probably be the biggest question to ask.

Car is a DD, but I've had 4.10's all this time, so coming from 4.10.... either isn't really an issue. My main concern is loss of acceleration vs. getting the power to the ground.
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Old Sep 15, 2011 | 08:57 AM
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Old Sep 15, 2011 | 10:05 AM
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With your mods I wouldn't go with anything other than a 12 bolt if not a 9" set up. Mine is a DD and I just finished a 3.70 9" with a billet posi from MWC. I feel a good amount of accelleration with them as opposed to the 3.42 and it will cruise at 1600RPM @ 70.

My argument here is that you should go with a better rear end while you are at it but with your mods, I would say you could benefit from the 3.90.
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Old Sep 15, 2011 | 12:53 PM
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^^ agreed. I don't think I would spend the money on gears and a swap on the 10 bolt. Going to 3.73 won't save your rear if you hook up.

The money may be better spent saving for a 12 bolt or 9" if you are serious about putting power to the ground. With 400rwhp you could blow up the rear with stock 3.42.

My 10 bolt rear with 4.10 just went out and I just have bolt ons. I ordered a 9" and went with 3.90.
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Old Sep 15, 2011 | 04:35 PM
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Originally Posted by TORK?
^^ agreed. I don't think I would spend the money on gears and a swap on the 10 bolt. Going to 3.73 won't save your rear if you hook up.

The money may be better spent saving for a 12 bolt or 9" if you are serious about putting power to the ground. With 400rwhp you could blow up the rear with stock 3.42.

My 10 bolt rear with 4.10 just went out and I just have bolt ons. I ordered a 9" and went with 3.90.

Those 10 bolts are really that weak? How much is a used 12' or 9' with 3.90's running these days? What did you pay for your 9'?
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Old Sep 16, 2011 | 07:39 AM
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I got a MWC center section with a Moser stamped housing, Moser axles, and I had to get a longer driveshaft made. All in all I'm in it for 2700 bucks.
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Old Sep 16, 2011 | 06:04 PM
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Originally Posted by nik1703
Those 10 bolts are really that weak? How much is a used 12' or 9' with 3.90's running these days? What did you pay for your 9'?
I broke mine shifting into second gear at the track after a semi-soft launch.

Used the rears are anywhere from $1700-2100. I bought a new Moser 9" from Bob@BruteSpeed and the rear is ~$2500 shipped.
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Old Sep 16, 2011 | 08:04 PM
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Just FYI you can't even feel the difference between 3.90 & 4.10 you would hafta drop to a 3.73 to even feel the difference. or even better... I think 4.10 is perfect with a 28" tall tire!
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Old Sep 17, 2011 | 01:09 AM
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Go 3.90 and be easy on them and they will last. M6s are so destructive. Do a full rear end rebuild (bearings) if you haven't recently.
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