ok, ur all probably tired of answering this, but...i cant find a decent answer by searching the threads. here are my specs. 90 firebird, tbi, 700r4 tranny. pretty much stock except for the k&n and flowmaster.

i read that 3.73 will work fine with the 700r4 and 3.42 is better for the t-5.

but i also read that 3.73 is out of the power band for my lo3. that is unless i get like an lt1 cam, which i dont plan on doing for a while.

so would i be better off going with the 3.42 cause i hear the 3.73's will hurt my 1/4 mile times?

 

Ok, the higher the rear end the faster you will be off the line or at least just spin your tires, but you will have less top end, mostly with higher gears you see better 1/4 mile times if you have enough motor to spin it. Now if this tbi is a 305 like I suspect since you said it is stock, it sounds like you are pushing around a little less than 200hp, i have a 350 tbi pushin little over 317hp and 3.42 gears also with 700R4, so in comparison I think the 3.42 gears would go nicely under the rear of your car. Hope I helped a little.

 

I'm currently running 3.73's with my T-5 and find them perfect but they would probably be a little short for a 700R4.

 

It really depends on what you plan on doing to your engine. Gear swaps can get expensive, so you want to be careful on your choosing. I have an LO3 as well, but it can breath and pulls to 5,500rpm in 1st and about 5,100rpm in second, so I have decided to go w/ 3.73s. But I also have a T56 that is finally going to get installed in about 3 weeks. My engine mods so far are not that extensive actually-headers, high flow cat, flowmaster, open element, 670 TBI, and MSD 6A and coil. Stock cam and intake for the time being.... so even if I was to stick with the 700r4 I'd go 3.73.
I guess it really depends on what you plan on doing to your engine in the long run.

 

I am planning on running 3 42 in my rear on my 305TPI b/c its a daily driver too and doesnt run at high Rpm;;s
Aj

 

Go with the 3.73's. I had an 84 Z28 with a 700R4 that came stock with 3.73's. I have 4.10's in an LB9 305.

 

Gear swaps can get very expensive, so your doing the right thing by hesitating. I just installed 3:73's with the zexel posi carrier. HUGE improvment!!! I can't compare it to the 3:42 cause I never had them, but the 3:73's are pulling like crazy. Highway RPM's are not bad either. I do beleive the 3:42s may be better for the stock engine, cause even with my mods (cam, headers, exaust, ignition), with my 700R4 it still seems almost too low of a gear. But I'm happy with them.

 

what bout 3.55's could that be a possibility? :rockon:

 

Listen to me, I think I can answer the best for you.

With 2:73s and stock cat-back with a flow, burnt plug wire, I ran a 15.41 @ 92mph

With 3:73 posi, Hooker cat-back, new plug wire, I ran a
15.32 @95mph

I didn't match the gears to my cam.

Go with 3:42s if you don't plan on a cam swap for 1/4 mile performance.

 

3.23 or 3.42 for your current mods. The L03 will run out of breath with 3.73 or higher.

 

If he plans on leaving it with the set-up the exact same for the rest of his car's life, then maybe. But who's gonna do that? He'll be pretty upset if he's gotta change the rear after he installs a new intake or throws some headers on there. Think about what you're going to do to the car in the long run and get the rear to match that, otherwise it's gonna hurt when you need to spend the money to change the rear again when it could be going towards something else

My LO3 pulls to 5,500rpm in first and 5,100rpm in second, and that's without ever taking the intake off. That is with the stock rear end as well. After my posi and gears, I expect to be able to get more like 5,300rpm outta second. Look at my mods in my post further up. It's really not that hard to get our engines to breath.
Go 3.73 and you will be much happier later on down the road once you've modded your engine, or if you're thinking about it, after you put a new engine in there.