# Changing gears 3.73 or 3.91?!?



## 04Black Goat (Dec 5, 2009)

I want to switch my diff soon to 3.73 or 3.91 gears I am goin to be racing the car at the track so I want a strong rear. I want to know what brand to go with and what people are running gear ratio wise? I know there is richmond and motive gear but I wanted to know the best one to go with, and I am goin to do the install myself if any sugestions please let me know thanks


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## Vettekid1992 (Jan 23, 2010)

i cant believe no one replied yet lol!!


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## Rukee (Feb 8, 2007)

What kind of track?


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## 04Black Goat (Dec 5, 2009)

1/4 mile drag I have headers and I am goin to cam it by the summer and mabe in the way future supercharge it


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## 87GN06GTO07IRL (Aug 10, 2009)

If it's an auto 3.73's, if it's a stick 3.91's. On a side note i always laugh when people tell me you'll have less top speed with 3.91's! Like our cars will really reach redline in 6th  This isn't the days of four speed sticks anymore people!


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## Vettekid1992 (Jan 23, 2010)

its a stick... thanks guys


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## 1badass06goat (Apr 20, 2010)

so whos making gears these days on our cars? thats one thing i'm looking for ..... i was looking for 4 10 gears.... but can't seem to find them....any idea if they are out there....?


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## danfigg (Sep 27, 2009)

*re*

here is my input on this. With the stock gear 6 speed we are just shifting into forth at the finish line. Not sure about the automatics but if the overdrive gear is an actual gear and it will upshift into overdrive at full throttle then I would say that the autos can use a steeper gear. Now with the 6 speed launching it out of the hole is important to get a good 60 foot. But getting a good top speed MPH is also important and you are only gonna knock off a few tenths at the end of the quarter by adding horsepower but keeping the stock gears. Your still crossing the finish line at the same RPM and the Same MPH unless you can get into fourth as soon as you can. I would imagine any time after the 1/8th mile. Im not sure what gear we are in by the 1/8. On one outting at the track I held 3rd gear until the end hitting the rev limiter and had my fastest run but the slowest MPH 60 ft 2.25 330 6.091 1/8 9.208 MPH 79.39 1000 ft 11.829 1/4 14.12 98 MPH----danfigg


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## dustyminpin (Jun 19, 2006)

I've got the A4. What kind of gas mileage would I lose going from the 346 to a 373?


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## GM4life (Mar 18, 2007)

1badass06goat said:


> so whos making gears these days on our cars? thats one thing i'm looking for ..... i was looking for 4 10 gears.... but can't seem to find them....any idea if they are out there....?


Here you go: GTO WHEEL HOP AXLE AXLE GFORCE1320 GFORCE ENGINEERING GFORCE1320 SPOOL GEARS


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## Rukee (Feb 8, 2007)

If you buy the GTO chevy 12 bolt drop in diff you can get ratios all the way down to 5.46 to 1.


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## dustyminpin (Jun 19, 2006)

My avg. mpg dropped from 18 to 14 with the cam/heads/intake swap. I don't want it to drop any lower while it's still my daily driver. Again I ask, what will a 373 do to your gas mileage vs the stock 346. Also, what will it do to your top end?


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## 87GN06GTO07IRL (Aug 10, 2009)

Top end will be way better. 6th will actually do something.


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## dustyminpin (Jun 19, 2006)

What if you've got the A4 then? Same results? Will it kill the gas mileage?


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## danfigg (Sep 27, 2009)

*re*

looks like alot of hopes and dreams with that Gforce website. They hope some one will pay 1000.00 for a posi unit and 700.00 for rear gears oh and lets not forget the 3900.00 for the 12 bolt housing. I'll keep the rear stock with the exception of axles and stubs------danfigg


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## 87GN06GTO07IRL (Aug 10, 2009)

dustyminpin said:


> What if you've got the A4 then? Same results? Will it kill the gas mileage?


You will still have more top end since 4th is an overdrive and not a 1:1 gear. I don't know the ratio of 4th on an auto, so i can't say how big of a hit mileage will take, but it should only be an m.p.g or two unless you have a really heavy right foot. 3.73 is a good choice for autos, 3.91 for manuals due to the trans gearing.


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## jetstang (Nov 5, 2008)

Going from 3.46 to 3.73s is only going to make a couple hundred RPM difference at 70 MPH. If you had a 2.76 gear it would be worth it to change to a 3.73, and the car will really wake up. But, if you are only changing .30, the expense to do this is not worth the gain. You will probably only pick up a tenth or so. 3.46 is a really good ratio, stock Z06s have 3.42s. Now, if you are changing to 4.56s, that will wake the car up at the strip.


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## 1badass06goat (Apr 20, 2010)

GM 4 Life ur the greatest ~!~ .... lol I've been looking all over .... ( that's whats brought me to the forms ) i'm a rookie / newbie to forms

Thanks for the info


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## danieloneil01 (Dec 17, 2008)

Stop worrying about gas mileage in the goat. It's not a Honda. Get a pos DD that's good on gas if you're worried about it. 


Here's what 3.91 gears and some bolt ons will do with your A4. 10's


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## killdustindead (Apr 13, 2010)

if i buy gears, do you need to buy anything else other than the gears and major install kit? on that G force website the major install kit says it doesnt come with side ajuster roller bearings, would i need to buy that also to install the gears properly?


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## jpalamar (Jul 22, 2008)

jetstang said:


> Going from 3.46 to 3.73s is only going to make a couple hundred RPM difference at 70 MPH. If you had a 2.76 gear it would be worth it to change to a 3.73, and the car will really wake up. But, if you are only changing .30, the expense to do this is not worth the gain. You will probably only pick up a tenth or so. 3.46 is a really good ratio, stock Z06s have 3.42s. Now, if you are changing to 4.56s, that will wake the car up at the strip.


I think the C5Z has different gears in the trans too.


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## AlaGreyGoat (Jul 6, 2006)

The GTO has a 3.46 rear ratio and the C5Z has the 3.42.
They both have the same M12 gearing.
Here is a chart I posted earlier.

http://www.gtoforum.com/f39/gto-m6-gearing-mph-chart-15718/

Larry


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