hey everyone i have an 88 iroc 305 auto with 2.73's, and i want to put 3.73's in the rear and i was wondering how much torque and hp i would gain and how much it would cost to buy and get installed. thanks!

 

you wont gain any tq or hp, it will just give you a better mechanical advantage because of the better gear ratio, so your car will accelerate faster, and thus feel faster/more powerful, but it will limit top speed, increase your cruising rpm, and lower your gas mileage. cost wise i have no idea

 

If you have a extra $700/800 for parts & labor depending on your location. You been reading too much about gear changes and unless you don't need the money leave it alone.

 

If your looking for better acceleration and track use, for your 305 3.73 would be to steep for your combo, I would recommend using 3.42 gears. Better for economy and better acceleration than the stock 2.73

 

I replaced my 2.73s with 3.42s. I love it except that I lost too much of the top end. I am putting 3.23s in tomorrow, hopefully that's be the happy medium.

I have a TBI/auto car, not sure how it'll be different than your car though.

 

I have 2.77 now and can easily cruise at 40, even 50 in second, waiting to punch and flip to third (yes, i'm obnoxious). The fresh 305 seems to love the 2k to 3.8k rpm range, so I'm thinking the 3.73 might not be too much. Beside, a complete 10 bolt 3.42 is hard to find and I'm really sick of the sluggish 2.77. But, I definately hear what most are saying... the tpi setup really flattens out at 4k... but, dang it... seems like 3.73 would give the morning rush hour stop light rush that I crave... yes? f the gas & rubber!

 

We went from a 3.08 open to a 3.73 posi rear in my wife's 90 RS autocross car. It was FUN, but it also made us learn to drive an autocross course again.

Very tail happy, but VERY worth it too! DO IT!

We swapped in a complete rear end, so no clue on costs.

 

This is exactly what I am afraid of. I found a drum brake 10 bolt 3.73 posi rear for 200 obo in my area (this would replace my 10 bolt drum brake 2.73 limited slip). I would love the 3.73 gears but I am wondering if it is too much for autocross. I already have a very sensitive gas pedal and I'm assuming this will make it even worse. It's between either 3.42 or 3.73 gears for me.

Mike

Edit: Could a smaller rear sway bar be used to prevent the rear of the car from breaking loose as often?</div>

 

You'll just need to relearn that you have better acceleration, and on autocross, the extra torque/leverage is great to have, on the short runs from cone to cone.

 

well a smaller rear bar would introduce more static understeer into the suspension, but even so, it would probably be a lot to handle.
if it were me, id go UP on the front bar, go UP in rear tire size and use stickies for track days ONLY.

then look into good shocks and you should be set.
a good set of shocks makes the world of difference.

 

Actually..Bigger rear bars are not always better.

Biggest stock is 24mm, front 36mm

Best choice would be 36mm front/19mm21mm22mm rear, dependnig on the driver & the tires ability to stick.

Allowing a SLIGHTLY more rear body roll, helpsgthe downward pressure to plant the tires harder.

I wanna trade my 24mm rear for a 19mm/21mm rear bar.

 

For the LAST TIME people!!! Limited Slip and Posi are the SAME FRIGGIN' THING! Dang!

 

i have a stock 305 had 2.73's and in the 1/8th mile i ran a 10.6 put the 3.73's in and ran a 10.2 i was very happy with the change makes the car feel alot quicker

 

I currently have the 36/23 bars. Driving my car around town and pushing it in some turns the car seems ok with the rear bar the way it is but I think when I really push the car during autocross, it will prove to be too much.

What I put in bold is what I was thinking about when I asked the question about a smaller rear sway bar.

Also, Stephen, there is a 19mm or 21mm bar in the junkyard down the road from me... should I look into it?

The front bar is already as big as it will go. I would like to go up in tire size but I don't want to spend money on wider wheels and/or stickier tires. Plus, for the class I am in, I can't go less that 140 for tread ware and it has to be DOT approved.

I'm going to be installing Koni Yellows on all 4 corners and I have Spohn SFC waiting to be installed. On a side note... I bought some Corbeau Forza seats to hopefully hold me in better. My legs were getting really tired by the end of the day...

Mike
</div>

 

I put in my 3:73 a week ago its a little much for my car but if you have plans for other mods like a new engine then it is a good mod.
kevin

 

ok timed my car today with factory 2.73s, 305 TBI 305. It was 8.8 with a little chirp in 1st and 2nd.

Will post up what my 3.73s show later.

 

8.8 0-60?? If so, WOW! I knew 305TBI/Autos were dogs (i had one) but i would have guessed a slightly faster 0-60.

 

Don't go outta your way. You can if you want, but I'm not sure I'd wanna know the shipping on an item that big.

 

How much top end did you lose? 150mph to 140mph?

 

Engine was screaming at 110, now it's more "normal" sounding

 

Shut up... I'm working on it lol

 

Its ok mine went 7.2 secs lol thats so bad!
kevin

 

im considering the same swap... it should put you at like 3900 rpms when you finish the quarter mile in third... which is good because the power band runs out after 4k

 

I wonder is this with your 3.73...?

 

Ya why?
kevin

 

limited slip and posi are NOT exactly the same thing. It's like Chevy and Camaro. Limited slip is a type of posi. A true posi doesn't allow slip for corners and turning. Like a tractor or dragstrip only racer. I know its mincing words but still.

 

Posi and Positive Traction are trade names for the Eaton brand limited slip that was used in the Chevy 12 bolt and 8.2 10 bolt. The name Posi is a registered trade mark for Eaton. Limited slip and posi ARE the same thing. Auburn calls theirs a Sure Grip (Mopar), AMC called theirs Safety Trac, Spicer calls theirs Power Lock, Ford is a Traction Lock... All of these are limited slip, just different names. The Eaton Posi name is the one that caught on and most people use that name to describe all limited slip differentials. Posi IS limited slip.

A spool locks both axles together and does not allow any slip in corners. This is what is used for drag racing.

 

Planning on putting 3.73's in my car too.
It won't be for a few more months, but.
Going along with our cars being slow, don't know what my 0 to 60 is off the top of my head.
But ya do feel kinda stupid when Jr Dragsters are going faster then you.
Just my 2 cents.

 

Thank you, thank you, thank you big gear head!!! If I hear another person misuse "posi" again ... I've said this before ... I think I will scream! I've said this same thing over and over, and for some reason, people still think "posi" is the correct term for a limited-slip differential. Now blp226 is saying there is a difference between a "true posi" and lsd. They do make locking rear ends, but if I'm not mistaken, those are not referred to as "posi".

 

full ack @gcgarner and big gear head. posi and lsd are the same effin thing ^^
i will put in 3.42 and posi into my formula's rear end this winter, i feel 3.73 would be too much with the 700r4. i might end up doing a t56 swap later down the road, so maybe i'll upgrade gears again at this point

 

ownor, you will NOT be disappointed in the 3.42's. That's what I did with mine, and I'm pretty sure I would have been a little let down with 3.73's behind my TPI and 700r4. The 3.42 is plenty low enough for the around-town/highway driving that I do.

 

yeah, as you can see i have a stock 3.73 rearend in my 84 HO, that thing really hauls a$$, but then again it has a T5 and its powerband is way up higher in rpms than on any other engine used in the 3gen. for the formula, i will do a lt1 cam swap, exhaust and intake, and i feel 3.42 will be a really good choice for that with the 700r4. i dont drive on the highway a lot, but i guess milage would suffer quite a bit if i would be going 80mph (limit in austria) or even faster like most do. thanks for the input

 

ownor,
posi and ls are not the same thing, (did you notice how I could say that without swearing).
What they are trying to say is posi is like drywall for example. Everyone calls it drywall, that's not true though, it's a brand name, when it is actually sheet rock.
So now posi and ls are not the same.
Posi refers to one makers brand, while ls refers to all of them.
Just most people don't realize this until someone tells them, or they are to hardheaded to let anyone tell them they could be wrong.

 

But most of us don't CARE enough about limited slip vs posi.

SAME thing, different name, that's all. And 4 letters is easier to type than 12.....

 

@kcb, the point is they can't be compared really. it's like comparing cars and camaros. of course, every camaro is a car. every posi is also a limited slip. but not every ls (car) is a posi (camaro) see? or, in computing terms, it's like comparing a base class to an instanced object. anyway.. let's forget about this. it's like arguing about fruits (ls) and apples (posi) being the same damn thing anyway, talking about our cars, they are the same thing.

 

I agree that this needs to be dropped ... esp. since it has nothing to do with the original question. My problem is, to reference your "apples vs. fruit" analogy, some people are saying that all fruit is an apple. Posi is the trade name of a product used by a specific brand of lsd's. End of discussion.

Alright, let's move on.

 

The original question is 5 months old. Why was this brought back to start with?