I have a 89 iroc 350 with 2.77 posi disc rear and from a dead stop its nothing special but when it hits 30 it rolls. Im guessing its the gears which is making my launches suck. Anybody go from 2.77 to 3.27's or 3.45's? Let me kno how much better the new gears are.

 

On the FAQ board, there's a thread on the 9 bolt that's good, and also go to the Drivetrain board. All kinds of stuff on 9 bolt. I've found anything I need there and the thread on FAQ.

 

I'm in the same boat with the exact same year of car. The faq scuzz speaks of is a good one. In order to make your 9 bolt change over you have to change the carrier to the 3 series so that it accepts lower gears. Trouble is that parts are no longer made for the 9 bolt rearend. 3:73 is the only aftermarket gear you will find. Randy's ring and pinion has the install kit. I can't remember where I found a new carrier but it was $1000 bucks. Needless to say you will have $1700 or more in a weak rearend. I'm saving for a Moser 12 bolt. Hawks Thirdgen has a 10 bolt 3:73 used for sale but it's non posi.
Jerry

 

I believe 9-bolt direct sells all the parts you need to upgrade your rear end to 3.27, 3.45, 3.70 and 3.91 gears. He has spacers to run the series 2 carriers with the series 3 gears. I installed 3.91 gears in my rear end and I believe the cost was around 350 dollars. Search the board and internet for his site.

On your other question will 3.27 or 3.45 gears make a big difference I will say no. If you have limited cash buy a 2400 stall speed convertor and you will see a big difference. I had 2.77 gears in my GTA and switched to 3.27 gears and the car ran the same ET's in the quarter but the convertor made a big change.

 

I know it's old, but I'll add to this topic for future reference.


.....I went from a 2.77 to a 3.27. I would say it was enough to notice the difference, but nothing crazy. I then added a 2400 stall, and that made a much bigger difference. If I could do it again, I'd go 3.45's with a 2800, but mine still kicks ya in the pants compared to stock.

Oh, and I added a completely new (used) 3.27 rear instead of messing with a gear/carrier swap. Cost me less than $200

 

 

2.77's are a "decent" gear. Not great but not bad for the tpi powerband. I wouldnt bother going to a 3.27 gear. If you are going to put the time and money into it go with 3.45's. I ran 13.6 at 97 along with full bolt ons and 2.77's. Now with 3.45's im getting 13.4's at 100.

 

I agree.

 

i think my transmission is messing up in over drive it wont down shift when i floor it and it will go no where but when it gets to the speed that the gear it is in is suppose to be in it pulls nice. When i manually shift it its a monster chews tires up still doesnt feel like a possibly 13 second car maybe its because im in the driver seat and more worried about controling it. Also it surges at idle the iac was cleaned and reset maybe its one of the injectors is messed up causing that and the lack of performance my car has.

 

I couldn't get any parts from 9 bolt.com or 9 bolt direct but difftechnics in Australia replied back and all of the parts carriers, gears etc are available.
Here is the list of stuff to fit my 9-bolt from them.

From Difftechnics - Differentials and Gearbox Diffs and Gearbox Repair differential housing Conversions Modifications
Kurt Hidajat
Gears are $ 275.00

Install kit $ 115.00 (Major kit)

Posi unit $ 380.00

Freight $ 165.00



All in USD all parts are NEW genuine!

 

Oh yes 9-bolt.com is now diffsolutions.com. He doesn't have any carriers left. So I'm still thinking about putting $1400 dollars into a stock appearing rearend or busting the bank with 3K into a 12 bolt. It costs that much because according to Thunder Racing the 9 bolt PBR discs I have are not interchangeable to the 12 bolt. So I also need brakes, parking brakes, new sway bar adapters and the complete rearend which is $2100 by itself. A nine bolt is rated at somewhere around 280 HP and 370 ft lbs of torque.

 

All you'd need to do to get your pbr brakes to fit the 12 bolt would be to get a set of 10 bolt pbr backing plates. They should have the same bolt pattern as the 12 bolt flange. You could even use your nine bolt backing plates if you didn't mind routering the holes out a little. They're not far off from the 10 bolt pattern.