Gears & Axles - Need advice, what gears do I need for 12 bolt?

I have 3.73 gear in my Moser 12-bolt rear. Car is 383ci turbo shooting for 700+ whp, converted from M6 to 4L80E. I want to get lower gear, somewhere around 3.1 probably.
I'm not big into gears so asking for advice - which gears do I need that fit Moser 12 bolt and be somewhere between 3.0-3.1? Although I don't cruise that much but gas here costs $8/gallon :(
P.S. I'd like to try standing mile events also, so need some 190-200mph top end too!

3.23, 3.08 and 2.73 are common gear ratios

Pretty big gap between 3.08 and 2.73... The latter would make 62mph at approx. 1700rpm but slow me down at the strip I guess.
Could someone please point me to 2.73 that would fit? I can't find them on Summit somehow, perhaps I'm searching them incorrectly...

You might have a hard time without the manufacturer's number.

Someone else was asking about 2.73 and higher (numerically lower) gears recently and said Jegs or Summit didn't want to help him. It's pretty rare for someone to order that high of a gear. Most people are usually looking for lower ratios (numerically higher) like 4.11, 4.56...

Anyway, I digress...

I found 3.08's (which is in that range you were looking for (3.00-3.10) ):
http://www.moserengineering.com/gears/12-bolt-gears/12-bolt-3-08-p-s-gear-hoosier-gear.html

http://currieenterprises2.reachlocal.net/cestore/productsRE.aspx?id=1982


So you might have to call Moser or Currie or yet other MFR's.

Hope this helps.

I buy my gears from Strange Engineering. They can hook you up. Or go through one of the speed shops listed and they can work it out with you. I know Speed Inc. ships across the country. I'm at 3.23 and running out of gear through the TH400 myself. Once I hit the rev limiter through the traps it's gonna be time to swap them out.
http://www.strangeengineering.net/catalog/index.html
www.speedinc.com

You'll need to call Strange for a special build of your ratio. I don't think they stock it normally.

I guess 3.08 will be OK, 21% taller than my current gear.
However that link to Moser site says pinion is "30 Spline", but my 12-bolt description said "Moser 12 bolt with 33 spline axles", does that refer to different things?

Would this Motive 3.08 set fit?
http://www.summitracing.com/parts/MGR-GM12-308/

Guys do you think 3.08 is a good choice for my combo?

Is there smth. else I need to buy with the gear/pinion? Some installation kits or smth.?

Do I need anything else except gear itself when swapping gears? Any installation kits, or shims, or smth.?

Are you planning on doing the gears yourself?

Here's what's involved with a 10 bolt. Not too different, just to give you an idea:

http://www.pcmforless.com/index.php?option=com_content&view=article&id=124:10-bolt-gear-swap-f-body&catid=35:wrenches&Itemid=56

Are you planning on doing the gears yourself?either that or i'll have to give the shop all the details. We don't have many rear-end solid-axle specialists here...

If it's a shop, they should have the tools to set it up, so that makes a big difference.

Other than pinion shims, which they probably already have, or can get cheaper than you, I think you're fine. The rear works now, so unless you have noises, I don't think you need bearings or an install kit.

I guess 3.08 will be OK, 21% taller than my current gear.
However that link to Moser site says pinion is "30 Spline", but my 12-bolt description said "Moser 12 bolt with 33 spline axles", does that refer to different things?

Would this Motive 3.08 set fit?
http://www.summitracing.com/parts/MGR-GM12-308/

The Pinion has 30 Splines for the Driveshaft Yoke! Your 33 Splines are for the Axles!

Joe

If it's a shop, they should have the tools to set it up, so that makes a big difference.

Other than pinion shims, which they probably already have, or can get cheaper than you, I think you're fine. The rear works now, so unless you have noises, I don't think you need bearings or an install kit.as I said, not specialised shop, just a garage. So I have to source everything...

From that 10-bolt guide I understood that I should have shim kit at hand, can anyone show me how it looks/where to buy shim kit for the 12-bolt?

From this link I understand that there are 2 sets of shims required, is that correct?
http://www.hotrod.com/techarticles/drivetrain/gm_12_bolt_differential_install_guide/

One thing no one has mentioned is that there are 2 types of performance carriers for a 12 bolt, you need to know which you have to order the gears. There is 2 series but I doubt you have that. The carrier determnes what gears you can fit in it.

The Three Series carrier accepted ring and pinions that ranged from 3.08:1 to 3.73:1, while the Four Series carrier accepted ring and pinions ranging from 3.90:1 to 6.14:1.

I am not 100% on the above statement, as I thought I saw a 4 series once with a 3.73. I got the statement from the article below.

Read more: http://www.hotrod.com/techarticles/drivetrain/chevy_12_bolt_differential_install/#ixzz26TOpBnj6

One thing no one has mentioned is that there are 2 types of performance carriers for a 12 bolt, you need to know which you have to order the gears. There is 2 series but I doubt you have that. The carrier determnes what gears you can fit in it.

The Three Series carrier accepted ring and pinions that ranged from 3.08:1 to 3.73:1, while the Four Series carrier accepted ring and pinions ranging from 3.90:1 to 6.14:1.

I am not 100% on the above statement, as I thought I saw a 4 series once with a 3.73. I got the statement from the article below.

Read more: http://www.hotrod.com/techarticles/drivetrain/chevy_12_bolt_differential_install/#ixzz26TOpBnj6


I wasn't aware the 12 bolt had different carriers like the 10 bolt.

You can get most popular ratios for different carriers, so that is something to check out. I know you can get 4.10's for 2 series and 3 series 10 bolt f body carriers, so it may be the same for 12 bolts.

I did a quick check and it appears that 4 series starts at 3.73 and goes up. The 3 series goes up too 4.10s and goes down from there, so there is some over lap in the 3.73 to 4.10 range, but is you have a 4 series it appears the tallest gear you can get is a 3.73.

Check different vendors though, they may have different options. I just had a quick look on Moser's site.

Yes I discussed "series" with Moser before buying the motive 3:08 gear I've posted, they confirmed.
So are there 2 sets of shims required for 12-bolt? One set of 0.2x-0.3x and the other about 0.70"?