I've got an 89 Firebird Formula 350. I was wondering if anyone knows what rear gear ratio I have? I'm new to the scene and could use the help.

 

https://www.thirdgen.org/newdesign/tech/techdb.shtml

2.77 or 3.27 depend on your options(it looks like the dual cat, higher horse engine got the 3.27 ratio


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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, currant red metallic paint. Lots of other stuff...
82camaro

 

as did some non dual-cat cars cause i have a single cat GTA, L98 with a 3.27 rear


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*89 Trans Am GTA
*Moderator at www.transamgta.com

To hell with the GM vs Ford war. We must unite, as brothers to fight the plague that is overtaking the world...RICE

Tony

 

My '85 Z28 305 TPI (single cat, obviously) also had a 3.27 rear. You can determine your gear ratio by driving on the freeway in DRIVE if you have an automatic or whatever your 1:1 gear is in a manual. Drive at 70mph (I've heard other people say 65mph) and check your RPMs. If they are around 2700, you have a 2.73, if they are around 3200, you have a 3.27, etc...

 

70 MPH works for all the cars I have tested.

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If you live in Southeastern US, check us out!
South East Thirdgen

1987 Trans Am 305
14.88 @ 92.81

 

65MPH = 2100 RPMs for my 3:27

 

What tranny do you have and what gear are you in. You MUST be in the Direct Drive ratio (1:1) In a 700-R4 (4L60) its 3rd gear or "D". for a 5 speed, its 4th. It won't work in Overdrive "(D)"

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If you live in Southeastern US, check us out!
South East Thirdgen

1987 Trans Am 305
14.88 @ 92.81

 

2900 rpm @ 70 mph with my T5 in fourth, purple drive and white driven gears, 3.42 rear gears, 225/60R15 tires....

Pete

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Pete's Place
HiOutput Tech Page

83 SC..former V6...now 216+k mile LG4/5-speed.. 14.891@95.54

 

Ummm.... Skip all of that stuff and open your glove box (center console storage box deal), look at the Sevice Parts Information label (has all of the three digit RPO codes on it) and find the three digit codes that start with G. They are the ones for the rear axle. You should see G80 (limited slip differential) and either GW6 (3.27:1) or GH3 (2.77:1).

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club