I went to a shop that works on rear ends. I asked if he could put 3.42 or 3.73 gears in place of my stock 2.73 gears. He told me that I would need a different posi unit to do so.

Now I realize the posi unit that comes stock on my 94 Z28 isn't the greatest for drag racing because it's built to drive on the street. I think i remember seeing a Z28 burn out down the track with the majority of smoke coming from the passenger side tire.

Do I really need a new posi unit? How much should I expect to pay for gears & the installation? How much for a new posi unit and which one should I be looking for? All I care about is straight line performance because I only drive my car once a week if that and I could care less about cornering performance.

Thanks for any help, I've been wanting to do this for a long time because the 2.73's feel like just a waste.

Eian

P.S. I'm located in northern california

 

First off, no you don't have to replace the posi to switch to 3.42 or 3.73 gears. But, when you order them you have to make sure they are for a 2 series carrier.

For new gears, an install kit, and a posi unit anywhere from $500 up to $800. It depends on what brands you get and where you get them from.

But, if all you are going to do is drag race and you plan on more power, i would save the money and go for a 12-bolt or 9 inch rear. Someitmes you can find used ones for a good price or maybe get a gp started.

My .02

 

Thanks, I have heard in the past that the 2.73's that come with my car are gears with a 2 series carrier. What exactly does that mean? I think I've also read that the z28's that came with 3.42's have a 3 series carrier.

Anyways. My car is an automatic. I don't want to make it into a drag car. I just want high 13's out of it. Right now I have Slp loudmouth exhaust(w/dynamax bullet instead of reasonator) and Moroso air intake(yea not much, but hey i'm working on it). I ran it at the track and got a ****ty 60 foot time on street tires. It didn't help that everyone drove straight through the water when you're supposed to drive around it with street tires. I normally get MUCH better traction off the track when driving around town.

So it ran a 14.3 at 98.78 mph with a 2.36 60 ft. And the car is originally a washington car if that makes a difference. I hardly ever drive it to keep the miles low (48k).

I don't want to install the gears myself because I heard if you do it wrong you will end up with a 'whining' sound and broken gears in the future. How much should I expect to pay for labor?

What time should I expect with 3.73's? Hopefully the track isn't wet the next time i go.

Thanks for the help,

Eian

P.S. I've considered getting a 12 bolt but everywhere I look I see $2,000 price tags with the ABS hookups. Plus I feel that if anything were to break in the future it will probably be the tranny first, correct me if I'm wrong, but the overdrive trannys they put in these cars arn't that strong.

 

With a numerically higher gear the ring gear has to be closer to the center since the pinion has fewer teeth (and thus a smaller radius).

You can get gears in sizes up to 3.73 that are specially made to fit a 2-series carrier. So unless you want a steeper gear, you will NOT need a new posi.

As far as stuff breaking:

Chances are with your power levels, your rearend and transmission will both be ok with street tires or drag radials.

Now if you start using ET streets and skinnies, you're going to be putting serious strain on the rearend, and there have been situations where a stock motor has shattered it like glass with a strong launch.

Good luck

 

1) The ring gear thickness will compensate for the position of the ring gear in relation to the pinion gear, so nothing else is necessary as long as the gears were ordered for a series 2 carrier.

2) 4.10 gears are also available for a series 2 carrier from most companies. I have never seen anything lower than a 4.10 though.