Firechicken350

Thinking of upgrading my gears and transmission, I have a stock 96 firebird 5.7 6speed, trying to find what my gear ratio is. Any ideas? And any suggestions on where to buy performance transmissions? Want something that can handle more power than stock thanks!!

Injuneer

All 6-speeds from 1994-2002 left the factory with 3.42 rear gears. This shows as RPO "GU6" on the service parts tag.

I ran my T56 with 765 Hp/750 lb-ft for 2 years and it was starting to show signs of stress when I replaced it with the TH400. Still shifting fine, but guy who bought it for his high HP S/C application had to do a rebuild for a couple of worn bearings. Unless you are approaching the kind of HP, stock trans should be fine. The stock 10-bolt rear is going to fail before the T56.

Firechicken350

I was thinking about upgrading to a ford 9" rear end, installing 3.70 gears and having moser install the attachments and other things I'd need, any suggestions on if this would be a waste of money or a good idea?

Injuneer

What HP level are you running?

My recommendation would be to stay stock below 400HP, move to the 12-bolt up to 750 HP, the Strange (Dana) 60 to 1,000 HP, and the 9-inch above 1,000 HP. In basic form, the 9-inch is not a lot stronger than the 12-bolt, but there are a lot of upgrades that allow it to handle big HP.

The 9-inch has some negatives:
-highest mechanical power loss (10% loss, vs. 7% for the 12-bolt and 5% for the 60).
-heavy weight
-pinion shaft 0.75" lower than the 10-bolt/12-bolt increasing driveshaft u-joint wear.
-pinion shaft offset to one side (not on centerline of chassis) causing potential issues with the DS tunnel.
-requires bulky fabricated torque arm mount that reduces the advantage of the "quick change" ability.
-limited choices of limited slip differentials.

I would also question the choice of 3.70 gears. That would increase the torque at the rear wheels by about 8%. The first swap I did, back when the car still had the stock T56, was 3.73's, and it wasn't enough of a change in my opinion. I wished I had gone with the 4.10's. With the T56's two steep O/D gears, you give up virtually nothing with the 4.10's.

In my opinion, depending n your current, or future, HP level it would be a waste of money.

Moser 9-inch torque arm mount - this is a 97 30th SS with 1,350 HP:

Firechicken350

Thanks for all of the info! My power goals are around 750hp, plan of getting a 383 forged kit, ported heads and Intake and getting a supercharger, in your opinion will the 12 bolt be able to handle the supercharger? And I've been told different things about the 4.10s, some say that it doesn't give you any loss of gears but others say it makes first gear mostly useless, but I think I'll go with the 12 bolt with 4.10s! Thank you!

Injuneer

Personally, I'd leave it alone until you build the new engine.