This is a quickie!

I have a 1985 tpi firebird and Im building a supercharged 350. I want to drop down to 2.73 rear gears to get each gear longer. (Not looking for the jack rabbit take-off, but the top end speed.)
I ran across this is jegs:

2-Series fits 3.08 and numerically lower carrier.

3-Series fits 3.23 and numerically higher carrier.

Can anyone quickly explain 2 and 3 series ring and pinion sets?

 

The diameter of the pinion gear changes to fit enough teeth for the numerically lower gear ratios. The carrier has to change then to keep the ring gear in the right spot.

 

So that meas, since I have 3.23 gears on my posi rear end now, I will not be able to go down to 2.73 without changing my carrier, right? Is the carrier the whole center part in the housing in the middle of the axle? I can change that to one that supports 2.73 and that also supports posi rear right?

 

Yes the middle section of the rear also known as the carrier or differential or in some cases the posi. You can get a 2 series posi carrier.

I wouldn't bother with what you are doing. You will find you will run out of HP before you run out of gear.

 

Yeah, you may be right, I was building a 500HP engine, so I figured I was superman. I'll stick with 3.23 and see how it goes, thanks guys.

 

323's & 5 Hundy. You will be Superman .If you do any thing to the rear , spend the money on a 12-bolt . You may feel the need to be like a jackrabbit down the road with that much power . speed safely

 

Ok, you confused the heck out of me, what do you mean by "hundy"?! And if I go 12 bolt, I would have to change the whole rear end right? That's buku money ! If Hundy has anything to do with the tranny, I have a t5 to toss up in there, that will do me justice no?
Another question totally off the subject! I can't get my signature pic to show, what the heck is the problem!?

 

Sorry Man Bronx slang for hundred . Yes the hole rear will have to be changed , 2,200 hundred or so . Its a toss up as to witch will go first with that much power . To change the carrier it will cost 4-5 hundred thats if you dont use a used one , then depending on your axles and rebuild kit (bearings) and time to do this you are looking at half the money for a 12-bolt . You will not be able to enjoy 5-Hundred HP with a T-5 and 7.5 rearend . All depends on how far you want to go .

Speed cost money , How much are you willing to spend.

 

Im feling you, seriously I am, however this is a back yard project and my first time, and I really don't have the money to spend completely changing the rear end. The $4K superchager killed me already. And 5 "hundy" is what Im trying to achive, I have two blueprints from race shops that say with the parts that I either have or plan to buy, I will have 553.64 HP & 561.31 HP. That's why I was asking to drop down to 2.73 gears, I figured with that kind of supercharged HP, I would have the best of both worlds, jack rabbit takeoffs and great top end with the tranny at 1.0 gear. I know very little about the inside of the rear axle, all I did know is that it's a 3.23 borg warner posi rear stock 1985. Someone said earlier that with I would sonner run out of HP before I run out of gear, but the math say with 18 tires, 3.23 rear end, and tranny at 1.0, Im bearly over 100mph at 5800rpm. Though it took alittle while, I easily reached that speed with my 305. As I said, this is my first time building an engine Iam learing as i go, Im mainly just comparing what the 305 did vs what everyone say my supercharged 350 will do. Im even having the cpu sent away so that the eprom can be programmed for maximum HP. I hope you're feeling me, over $2k for a 12 bolt is alittle up there, but $5 hundy for 2.73 gearing does'nt sound all that bad, even if installation does take it near $1k. What is your verdict?

 

You've done something wrong there. You'll be at about 3015 RPM at 100 mph.

 

If you're using that calculator on thirdgen.org, tire radius for a 18 rim and tire is 10 inches.

 

3876 RPM then

 

Dude, you're doing something wrong, radius 10 inches, rpm 5800, rear end 3.23, tranny 1.0, =106mph

 

Why on earth are you only running a 20" tire?

 

It's an 18" rim with a 1" tire. 20 inches. What do you expect, for me to go to like 19 or 20 inch rims or somethin!? The radius would still be 10.5 for 19" rims and 11 for 20" rims.

 

The stock tire height is around 26", a 20" tire is going to look pretty small.

 

My first motor I put in a third gen (Mild 350) rippet the hole driveline apart with 342's non world class T-5 & 26 spline axles in a very short time . Whitch is what came in 85 . Then the car sat for 7 years intill I found time & money for it agian . Just do not get discouraged & keep a opened mind . You are putting the cart before the horse. Thier is nothing wrong with what you are doing & driving the car with the rear you have in it , is the best thing you can do for now.
A 2 series carrier is no stronger the 3 series . Someone please correct me if I am wrong . I think the only get weeker in like the 411 range do to a smaller pinion gear . Please do not take any of this the wrong way some stock parts just blow .

 

Yeah, I hear ya, I was thinking that say way, I was putting alot of hope into that stock rear end, thinking I wouldn't have to touch it, but also doubting pontiac made it stroung enough to handle an engine three times stronger than what they put into it. I may have the same fate as you, waiting till I can invest in it again. We will just see how long this rear end lasts. Thanks dude.