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Thread: 3.90's vs 4.11 rear change
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08-03-2010, 12:05 PM #1
- Join Date
- Aug 2010
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- south
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- 1999 WS6
3.90's vs 4.11 rear change
I've decided to change the rear on my '99 M6 1LE. I need to get confirmation from this forum that the stock rear is 3.42. With recommendations of how much higher to go and why. The original window paper says it came "Tenser" limited slip rear, but I'm not impressed that that did much!! Is a version of Posi-traction that is better available? Any recs on this?
Thanks, bma2
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08-03-2010, 12:09 PM #2
- Join Date
- Nov 1999
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- over here...
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- 45
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- 25,709
[]D [] []V[] []D- 1999 trans am
i believe these are the rpo codes on your door sticker... see if any of these match up...
GU5 : AXLE REAR, 3.23 RATIO
GU6 : AXLE REAR, 3.42 RATIO
it's a copy and paste and i don't have time at the moment to verify...
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08-03-2010, 03:46 PM #3
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- Oct 2006
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- St. Clair Shores. Michigan
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- 55
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- 1,602
Navy Blue Metallic- `98 Formula M6 HdTp
All factory M6 cars from 1994 - 2002 came with 3.42 gears.
4.10's are by far the most popular swap for M6 cars.
I currently run 3.90's and I'm very happy with the added performance.Craig
Semi Retired Street Racer
2012 Lava Red Mustang GT Coupe Brembo/3.73's
Build Date 3/17/11, Last Lava Red GT
Gone but not forgoten
NBM `98 Formula M6 HdTp
1 of 1 Build Date 3/12/98
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08-03-2010, 03:51 PM #4
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- Feb 2007
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- San Diego, CA
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- 5,823
2002 Z28 A4 NBM- Sadly now demodded :(
Your car probably has a Torsen (TORque SENsing) limited slip differential. Yes it's a form of Posi. If stock then it has 3.42 gears.
67 Camaro: K-K + 797-z (look it up), 454/Th400/4.10 12-bolt = 6mpg, PS/PDB/PW tilt, tach, gauges...
2005 Corvette LS2/M6 Magnetic Red Metallic (What else would it be?) w/ Cashmere interior
2002 Z28: NBM/Tan, MTI smooth lid, smooth bellows, !AIR, !cats, 1-3/4" QTP SS LT's, 2-1/2" TD's with X-pipe, MagnaFlows dumped at axle, custom welded SFC's, MidWest Chassis body mount adjustable T/A, 3400 stall, 3.23 gears (was 2.73). Tuned: 343rwhp/357rwt (before TD's). Best: 12.559 @ 108+, 1.73 60' @ 3500' DA w/MT ET Street DR's.
Carbon footprint? CLOWN SHOE!
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08-03-2010, 06:57 PM #5
- Join Date
- Aug 2010
- Location
- south
- Posts
- 12
- 1999 WS6
3.90's vs 4.11 rear change
Looking for more 'pop' at the low end on the street. So I'd like opinions on changing my 1LE M6 3.42's to either 3.90 or 4.11. And is the 'Torsen' posi system 'OK' or is there something significantly better? I've been UNimpressed with Torsen at the drag strip. I've run 12.08/125.8mph on street tires and I never flat shift my engine. Don't really intend to return to the 1/4 mile... it's just for fun and trips with the wife. Opinions please.
Thanks, bma2
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08-06-2010, 12:35 AM #6
3.73 will give you a little more pop and make 6th gear more usable
3.90 tends to be noisy because of the number of teeth, harmonics - several comapnies don't sell them for that reason.
4.10 will give you more pop, can be noisier than 3.73, you will need to shift to 5th at the track, and of course will cost a bit in gas mileage.
If it's just a fun car then it sounds like 4.10s are for you.
The Torsen has no clutches so no maintenance or slipping, the other unit in use is the auburn which is a standard clutch based set up.
Our sposnor New Era has the gears and the posi unit - and I recommend the GM (AAM) gears - much more tolerant in set up and generally quieter.
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08-06-2010, 06:02 AM #7
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- Aug 2010
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- south
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- 1999 WS6
Thanks DaddySS.
So if I go with 4.10's, do most find interstate trips at 80-85mph are still OK in 6th gear?
And is the Auburn rear a huge improvement over the 'Torsen'? or only relevant at the 1/4 mile?
Thanks, bma2
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08-06-2010, 10:29 AM #8
2018 Tahoe - Silver - OEM
2008 Z06 - Velocity Yellow - BBE exhuast - Airaid CAI **sold**
2002 Z06 - Electron Blue Metallic - D1 - E85 - 701 rwhp 687 rwtq **sold**
2002 Z28: M6 NBM - cam and boltons - 396rwhp 357 rwtq **sold**
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08-06-2010, 08:09 PM #9
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- Jul 2010
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- sc
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black- 1998 camaro
?
when i bought my 98 z28 m6 it came with 4.11s what drive and performance difference does it do
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08-07-2010, 03:46 AM #10
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Navy Blue Metallic- `98 Formula M6 HdTp
Good info
But 4.10's will top 4th gear between 112-115mph at 6000rpm. A stock LS1 isn't going to hit that speed thru the traps. so hitting 5th gear isn't an issue. And a modified car with a higher rev limit would still be good.
BTW my 3.90.s only added 200 more rpm in every gear. 4.10's should only be another 50-100 rpm above that.
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08-07-2010, 09:06 AM #11
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08-07-2010, 11:54 PM #12
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- Aug 2005
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Red Tint Jewelcoat- 2008 Trailblazer SS
Shouldn't be shifting into OD gears at WOT
Seen cars with 4.56's go 131MPH in 4th (granted, 28" tire, but still).
All depends on set-up.
On a 26" tire and 4.11's....75MPH should be exactly 2000RPM. That is where mine sits....and I still get decent highway mileage.
Thinking I want 4.56's though.
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08-08-2010, 06:04 AM #13
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08-09-2010, 06:35 AM #14
- Join Date
- Aug 2010
- Location
- south
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- 12
- 1999 WS6
So it appears 4.10's in present stock rear are the ticket. Since I don't intend to flog the car at the strip, it should survive? I'm running the stock 17" WS6 wheels with 285's(Continental). Gonna leave the Torsen rear 'as is'. Local mechanic is offering $530 labor if I get all the parts---is that appropriate?
Any other things to consider?
Thanks, bma2
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08-09-2010, 07:07 AM #15
oh hell no, thats way too much. I payed 150 for mine. Id suggest if your the type that does his own headers that type of thing then this is no big deal either. Get a pinion depth guage from jegs or summitt for 99 and do it yourself. Its about a 2-3 hour job and you could save about $430 on the labor rate you quoted. Just be sure and read the breakin directions for the gears and folow it to the T...
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08-16-2010, 05:54 PM #16
What have you done to your car to trap 125 mph??
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