I have a '91 bird with the 305 TBI and a 700R4. I'm going to do work to the car as far as Exhaust, Manifold,Ignition,Cam. I'm going to run the car street/strip. I would like to put a posi in the car with 3.73 gears. Now my question would be is it worth building up the 10 bolt in the car or should I get a 12 bolt from the junkyard or one of the rebuild shops already done? I may want to drop in a 350 or 383 somewhere down the line.

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Nothing like driving your bird down to the beach at sunset!

a 305 with just bolt ons will not make any serious power and no need to worry about the axle yet, there are also no direct bolt in 12 bolts, you would have to get and aftermarket one.

The only way you could use a junkyard 12 bolt or 9" would be to convert the rear suspension to ladder bars or a 4-link. The trouble is that there is no way to mount the torque arm on a non third gen diff.

Your 91 will already have 28 spline axles. They're not as good as aftermarket 28 spline but are better than the older 26 spline. Have the axle tubes welded and install a rear cover with bearing supports and your diff will survive just fine.

I'm still currently running a 10 bolt that's been built up. I'll be switching to a 9" this winter just because I need a deeper gear and a diff that can handle a transbrake.

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block (times are for the current engine)

Best ET on a time slip: 11.447 altitude corrected to 10.99
Best MPH on a time slip: 119.42 altitude corrected to 124.86
Altitude corrected rear wheel HP: 493
Best 60 foot: 1.586

Racing at 3500 feet elevation with a typical race day over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

I'm thinking of dropping in a 383 in the future thats why I was thinking of the 12 bolt. Won't a 12 bolt from a 91' GTA or TA direct fit in my car? I always thought when these cars are made and they are going down the line they don't know if the body is going to be a firebird a TA or a GTA or an automatic or stick so I would think these parts would be interchangeable?

there was never a thirdgen made with a 12 bolt. if you want a 12 bolt call moser or strange and be ready to spend around 2000 dollars.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

I'm used to the old Camaros and Firebirds, I just assumed the higher performance cars like the Z & T/A came with 12 bolt posi. What was used in these cars for performance?

well they did but GM used the parts that fit the engine, the early camaros with 396's and the 455 firebirds got 12 bolts, then wen the 455's and 396's were downgraded to 400's and 350's they went to the 8.5 ten bolt, then when power went even more into the crapper they went to the 9 bolt and 7.5 ten bolt (both mediocre) but the cars options and drivetrain parts allways reflect the power the car has. the 3rd gen has the worst tooling of all the F-bodys. if your just building a mild car or street/strip you'll be fine with the stock axles, but a race car aftermarket is your only option.

[This message has been edited by TempesT68 (edited November 23, 2001).]

All I have is a '91 bird with the 305 TBI.I'm thinking of dropping in a 350 or 383 and taking out the TBI but I'm not sure how the rest of the electronics will work without the ecm. I saw where someone talked to Richmond gear and they said the 10 bolt is only good to abot 400HP, and if I go the 350 or 383 route I'm going to build the motor to at or above that mark. I'm to the point of thinking of just selling the '91 and getting a 67-69 bird something I know about, these computers are killing me.

how much 4 the bird?
go get a gen 1,
hope u gots money....and u dont make trips in it to varying altititudes....
or u could always stick around and learn sumthing about one of the least complicated fuel injection systems on the planet

I live in Florida just like you so I don't have to worry about altitude. I check out all the boards and I see arguments for both sides, either stay with the TBI or go carbed.It looks to me as if it's cheaper and easier to go with a carb.