can't decide if its worth it 2.73 open to 3.42 posi

[black_aerocoupe]

in my 3rd gen 88 Firebird Formula
currently has a one wheel peel 2.73 10 bolt
a bunch of local guys have 3.42 posi 10 bolts out of T56 6 speed 4th gens ready to bolt in for less than $300
my 18" rear tires are getting old & hard...one will often spin not even laying into the gas much
4th gen rears are basically a bolt in, and it would eliminate my 2" wheel adapters in the rear
2.73 to 3.42 isn't that big of a difference...I'd much rather 3.73 or even 4.10 (700R4) but nowhere near as cheap as a factory assembly

That's the textbook ideal rear for your (as-stock) vehicle unless you need to go back and run 0 offset wheels. Or need a strength upgrade.

An '88 Formula starts life with a choked-head-intake ports engine, or a choked-port-intake-mani that is matched better to 3.42 than it would be to 4.10.

Drivability around town and country is better with a 3.42. Unless you're putting mega hwy miles on, or otherwise prioritizing mileage and need to keep the 2.73, go for it, absolutely.

A V8 '98 was an Auburn, with an SLP Torsen option. Ideally, a '99-02 rear has a standard (no frictions) Torsen, unless the car was SLP-"upgraded" to an Auburn those years.

3:42`s are a good compromise gear .You get good acceleration and decent gas mileage. I have a set in both my 1979 -28 with a 4 speed supercharged 377 small blok and a 1981 El Camino SS 350 small block turbo 350 .and both get around 22-5 MPG. with a 26 inch tall tire at 2500 rpm

Your tach, speedo, math or all 3 are off.​

​

 

[SRGN]

Do it. You will notice the difference, and the car will be more fun to drive. I've gone from a 2.73 to a 3.23 and noticed a vast improvement. Plus the 4th gen rear disc brakes are much better.

 

[big gear head]

Just a warning, if you have been doing one wheel burnouts and the tread on the right tire is less than the tread on the left tire then you need to replace the tires. If you use a LSD with tires that have uneven tread wear, unequal air pressure or different size tires then you will wear it out quickly and cause the oil to run hot.

 

[GoldenOne7710]

I did a 2.56 swap to 3.42 ratio behind a TH350. Made all the difference in the world. Can't go wrong behind a 700R4.

 

[80sz]

You done yet ??? What’s takin so long

 

[Jaxons nasty z]

in my 3rd gen 88 Firebird Formula

currently has a one wheel peel 2.73 10 bolt

a bunch of local guys have 3.42 posi 10 bolts out of T56 6 speed 4th gens ready to bolt in for less than $300

my 18" rear tires are getting old & hard...one will often spin not even laying into the gas much

4th gen rears are basically a bolt in, and it would eliminate my 2" wheel adapters in the rear

2.73 to 3.42 isn't that big of a difference...I'd much rather 3.73 or even 4.10 (700R4) but nowhere near as cheap as a factory assembly
View attachment 83231

3:42`s are a good compromise gear .You get good acceleration and decent gas mileage. I have a set in both my 1979 -28 with a 4 speed supercharged 377 small blok and a 1981 El Camino SS 350 small block turbo 350 .and both get around 22-5 MPG. with a 26 inch tall tire at 2500 rpm

3:42 is like the perfect street gear for older cars with 4 and 5 speed tranys . I run 4:11 with super t-10 and the tires size is key . Im running 275/35r20 thats 27” tall and its great . Im in the process of raising and running 28/12-15 28” tall . With your short tires 3:42 is a pretty big jump from 2:73 . Gas mileage will change and no more cruising 70 or 80 unless you go to some new 6,7, or 8 speed tranys . I absolutely love 3:42 for a street machine

 

[1980RS]

I can tell you this, I put 4.10 gears in my 94 Z/28 with a 2.66 low T56 and it was a blast to drive from the 3.42 gears but if I were to have a 700R4 then I would use either a 3.23 or 3.42 and the most I would use with that auto would be a 3.55 gear. 4.10 gear with a 3.06 low gear makes 1st gear absolutely worthless unless you have like 31" tall tire like what we use in drag racing.

 

[xten]

I can tell you this, I put 4.10 gears in my 94 Z/28 with a 2.66 low T56 and it was a blast to drive from the 3.42 gears but if I were to have a 700R4 then I would use either a 3.23 or 3.42 and the most I would use with that auto would be a 3.55 gear. 4.10 gear with a 3.06 low gear makes 1st gear absolutely worthless unless you have like 31" tall tire like what we use in drag racing.

I agree 100%. I had 4.10's with a 700R and 1st was a joke. Distant memory. Went backwards to 3.89's (9") and wish I would have gone more shallow. Kid has an 8 sec. 1st gen turbo street car with 3.55's and he's going to 3.23's. He doesn't know it yet, but I'm going to steal his 3.55 pig.

 

[Jaxons nasty z]

in my 3rd gen 88 Firebird Formula

currently has a one wheel peel 2.73 10 bolt

a bunch of local guys have 3.42 posi 10 bolts out of T56 6 speed 4th gens ready to bolt in for less than $300

my 18" rear tires are getting old & hard...one will often spin not even laying into the gas much

4th gen rears are basically a bolt in, and it would eliminate my 2" wheel adapters in the rear

2.73 to 3.42 isn't that big of a difference...I'd much rather 3.73 or even 4.10 (700R4) but nowhere near as cheap as a factory assembly
View attachment 83231

Thats a no brainer . 3:42 with some 255/60 and youll be rockin . My second gen is 4:11 with bw super t 10 . I just put 15” on with 295/50r15 and i havent driven it yet but i know ive been here , its too much . Im going with the 28/12 15 to get the height i need with 4:11 . Your wrong if you think 2:73 -3:42 isnt much . Thats alot really . Do it and if you want to rock run short tires and if your not happy with the gas go with your extra set of taller tires . My opinion 3:42 is the perfect old school gear . Superman had 3:42 and i loved it being automatic

 

[Hogdaddy]

Personally, I like the 3:73 posi with the 700 R4 in my 86 truck. It has stock 15" wheels.