the vendors like summit and thunder sell a motive 3.90 ring and pinion set for 93-97 cars, but i've seen some folks mention 3.90 will not work on stock axle and some need a different diff? confused?

 

Motive gearset # G875390 will work.

 

There is a series 2 carrier and a series 3 carrier (doing this from memory at work but recall that 3.08 and taller gears are series 2; 3.23 and shorter are series 3). If your axle is stock, think you should have the 3.42 ratio (RPO GU6) in a manual trans car which would be a series 3 carrier, and would work with a 3.90 gear set. Also there are "thick" gear sets which let you run shorter ratios on the series 2 carrier.

 

Thanks guys. The G875390 is the one I ordered with the Ratech Deluxe rebuild kit.

 

A 1994 should have non-traction control 3 channel abs (there is wired sensor on the top of the center section) and there is a fairly fragile reluctor ring on the carrier next to the ring gear that sends the speed signal to the abs. That part is no longer available anywhere in the known universe, so busting a tooth off would be bad; the pickup is still available but is about $150 bucks.

 

I haven't seen a 3.90 (thick) set for 2 series anywhere.
The ABS reluctor ring does not have to be touched/removed for a gear change,it's pressed onto the carrier,not the gears.

 

Awesome feedback guys. Have any of you actually ran with 3.90? What kind of improvement will I expect from 3.42 to 3.90 with my mods?

 

Camaros/Firebirds with 3.90s' are not common,3.73s' are preffered for autos and 4.10s' for M6. Not saying there's anything wrong with going to 3.90s',just that they're not the preffered.

 

First off, FirstYrLs1Z, there is an old saying that "One picture is worth one thousand words", and .... the picture you posted is worth every bit of those 1,000 words. Beautiful photo!!!

For foxbat, you do know that your 6 speed manual transmission has a 2 to 1 reduction (i.e. .5 input to 1 output ratio) sixth gear overdrive in it, right?

This makes the FINAL overall drive ratio between a 4.10 to 1, and a 3.90 to 1 ratio rear gear, when your car is in 6th gear, only different by (4.10-3.90)/2 = .1 revolution! (i.e. 2.05 vs 1.95 final drive ratio ..... when in 6th gear). Do yourself a favor and get the 4.10 gearset for your M6 equipped vehicle.

On a personal note I have had three(3) different ratio rear gearsets in my M6 car, ( See signiture below), namely, 3.42:1, 3.73:1, and 4.10:1, and ........ I'm currently looking to go to either a 4.30:1 or 4.56:1 gearset this coming Spring.

Hope this info helps?

 

I always try to post meaningful pictures,having a good digital SLR and photoshop helps.
4.56s',hell yeah. I'm A4 with 4.56s'. 'Fear the Gear'.

 

There are also couple of calculators on this web site that can give you an idea of what to expect with various final drive and tire combinations:

https://www.camaroz28.com/extras/

https://www.camaroz28.com/calcs/rpmmph.html

Also did not intend to imply the reluctor had to come off the carrier, only that when you have the carrier out, be careful as the reluctor ring is the most fragile piece in the rear end and there is no source for a replacement. GM actually uses a special tool that is a reluctor ring protector when the carrier is out.

 

Thanks for the good info. I had considered both 3.90 and 4.10 gears with the M6 and decided to go with the 3.90 based on the info I saw on http://www.f-body.org/gears/

It seems with 4.10 I would have to shift to third with our engine redline at 5500 in order to hit 60, while with the 3.90 I'd hit 60 in 2nd gear at 5500. Also, I do a lot of highway driving and I like my cabin as quiet as possible at 70-75, so even though the difference between 4.10 and 3.90 is small, any noise reduction and fuel savings helps

 

Why is your redline only at 5500? I run mine to 6k with no issues.

 

If i'm not mistaken LT1 tach redline is 5500 and they start dropping off power between 5200 and 5500 from other dyno graphs i've seen. my motor is mostly stock aside from mods listed. am i shifting too early at 5500?

 

You'd be OK with shifting it at 5,500 RPM if it was bone stock, but its not bone stock. You've made changes to help it breathe better, and those changes make the most difference at higher RPM. And, why is not shifting to reach 60 MPH important? If you're worried about 0-60 MPH time, its just a statistic, and virtually meaningless. The stock rev limiter in your car is set at 5,886 RPM in 1st gear and 5,805 RPM in 2-6th gear. Do you know what LT1pcmtuning set it at when he tuned it? Have you ever hit the rev limiter?

Go with the 4.10's and shift at higher RPM.