I have an 89 camaro rs with 305. It currently has a 2.73 non posi rear end. Can i expect any performance gains if i swap to a 3.23 posi rear end that will be noticeable? Will the car have any more noticeable pickup?

Yes it will. 2.73s are really just highway gears. 3.23 IMO (and 3.27 BW) are a really nice balance of performance and drivablility on the highway. If you got to 3.42s you will have even better pickup but lose some of the nice cruising ability. I had both and prefer 3.27s.

I went from 2:73 to 3:42 and did not see any noticeable differance. In fact I was disapointed. But that could be pesonal preferance. If you are expecting a big change your not gonna like them, not enough spread in the ratio. It will make your speedo jump up about 10 mph than your actually going. Now if you go with 3:73 you would think you had a new car. Now some say they make a tuneport car wind up too fast. I dont know I havent put 3:73's in my 88 yet but I was happy put them in other cars I have owned.For street I would not go lower than 3:73's unles you have a 5 or 6 speed(preferably a 6 speed if you still want driveability) in other words, no 4:11 with an automatic

With a 170 HP 305 TBI don't expect a lot of improvement. But if it is affordable it would be a nice upgrade. But I would not spend a lot of money for it.

it's not worth it. i changed out my 2:73 for a 3:42 and i want my 2:73 back. i'm not sure if the car performs better but the speedo gets on my nerves. when the car is running 70 mph the speedo says i'm running 82 mph. the one thing i did notice was my gas milage went down.

Im sure you will feel a little difference. I am switching the 4.11 to a 3.42 in my 91. I have a 5spd. and its too much gear.

I'll take your 4:11's!

For everyone complaining about the speedo reading off, just change out the speedo gear for the gears you have. Done!

Not to hi-jack, but tony I am running 4.10 and doing the t5 swap now how did your car perform?

I am planning on doing some light mods to the engine, nothing too much, i already did the cat back exhaust. Also did open element on the air cleaner. I am considering swapping in a larger TBI unit with a stock 4bbl manifold and an adapter. I can get a 3.23 posi for 100 bucks, thought it might be a good upgrade over the 2.73.

Back in my ole 305 TBI days I swapped from 3.08's(M5) to posi and 3.73's and it was night and day difference. At first it felt slower, but once I laid into it thru all the gears at the track it was a whole different story. Went from 15.5's to 15.0's with no other changes. The 3.42 should be perfect for an auto car.

Been down that "Speedo gear" Road before........never could find the right one
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In an automatic car, you'd want to go lower with your gear i.e. 3:73's not higher (3:42) to "feel" the most differance because you transfer less power to the rear wheels with an auto or a "slush box" as some call it

For $100 I'd go ahead and make the swap. I usualy sell a possi alone for that. But remember......If you like doing burnouts, with a possi the rear will fishtail on you which it wont normaly do with a 1 wheel burnout so be ready

Sounds like we're both headed down the same path. For $100, I'd do it. I would expect to get a slight decrease in fuel mileage and a slight increase in performance in terms of a 1/4 mi time. Not so much from the launch b/c first gear is already pretty low in our 700r4, but from 2nd b/c it drops the rpm so much. With the higher ratio, the rpm will be a little higher in the hp band of our engines.

For $100 you're not only getting a better ratio, you're also getting a posi. Hopefully, it also has disc brakes. You'll be getting an increase in performance in terms of traction and braking. Those alone are worth it.

The big question is: will the trans shift when you need it? My stock trans wouldn't shift before the engine ran out of ponies. If you're experiencing similar problems, I suggest a couple simple upgrades: a corvette servo for a firmer shift; and a governor tuning kit (if it allows you to lower the shift points).

1234brd: Once I got my trans to shift at a more appropriate rpm, I get a wicked fishtail during the 1-2 shift w/ my peg leg rear end. I'm looking forward to the day of having the advantage of a posi and putting down two black strips instead of just one.

$100 I bet I can find one laying around the shop. LOL

Man, you guys that said you didn't feel any difference between 2.73 to 3.23 must need a good tuneup or a full rebuild on your motor! I switched to 3.23 in my 89 L03 car, and the difference in takeoff was substantial. As far as gas mileage goes, it actually improved it when driving around town. Reason being, you don't have to mash the gas down as far to get moving with better rearend gears. As far as freeway mileage, I have a buddy who lives 400 miles from me, and I've made the drive up there with 2.73's and 3.23's, and both times I stopped at the same gas stations to fill the tank, so the difference in freeway mileage must be pretty insignificant as well. If you can't figure out how to change the speedo gear to match a new rearend ratio, you shouldn't pick up a wrench in the first place!

I do have a bit of a lag on shifting with the transmission. It works fine, but seems to shift a bit "late". If i leave the car in drive, not overdrive, it seems to ride better. I was considering investigating some kind of shift kit to improve shifting, not sure what to get.

Yea i agree. Ive had a car with 2.73 as well as a car with 3.42s...and now i swapped the 3.42s for 3.27s. I noticed the difference in all cases. The difference from 3.42 to 3.27 is less noticable however. Just lowers the RPMs on the highway and doesnt really hurt the fun factor on back roads.

how about changing the gears in the trans to get some nice highway gas mileage. from 1 to 2 is ok but i would like to have a slightly larger step from 2 to 3 and then change 4th so that it has the same rpm's at 70 as it did with the stock rear end gears?

That would be WAY more work than just swapping rear ends. Im also not sure you would get anything from it. 700r4s already have a pretty decent overdrive.

but instead of 2,000 rpm with 2.43 you would be running a lot highter, and i want to run freeways without gas mileage loss.

Read again....Never said I couldnt CHANGE the Speiedo gear.....said I couldnt find the right one Only 3rd gens I know with a factory 3:73 were 5 speed cars and the gears arent the same that I have found. Now.... the speedo gear out of an S-10 should work but I havent tried to find one. So lets try not to be so insulting on here
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That's Speedo......not Speiedo

Might I suggest visting this site:

http://www.transmissioncenter.net/sp...n_______va.htm

Sorry dude, I really wasn't trying to be a jerk or anything. If you get the gray, 15 tooth drive gear for the output shaft of the trans, I guarantee you can find the proper driven gear for 3.73's. All f-bodies that were 3.23 or numerically lower used the red, 17 tooth drive gear. When you go 3.42 or numerically higher, you need to use the 15 tooth gear to be able to get a driven gear that'll match up correctly. In fact, I'll be extra nice and figure it up for you. If you're running the common 245/50/16 tire size, you'll need a 44 tooth driven gear with the 15 tooth drive gear, and you can buy both gears from the link that 89IROCZ28 posted. I used the calculators provided on JAM Performance's website. They have a tire size calculator on the left, and the speedo gear calculator on the right of the page. So if you have a different tire size than 245/50/16, just use their calculators to figure out which combo you need. Here's the link: http://www.5speedtransmissions.com/calculators.html

Hey red, I basically have the same issue on mine since I switched from 2.73 to 3.23. It shifts into OD too early (about 35 mph) and kinda lugs, so I just leave it in Drive until I reach about 40-45 mph, then bump the shifter into OD. A shift kit may help, but I'm betting recalibrating the governor with a governor recalibration kit would probably be the best way to cure it. I'm just too lazy to fool with it on mine, and I'm so used to manually shifting from Drive to OD, I don't even see it as an issue. Btw, if you're considering a shift kit, TransGo are the only ones worth considering. Get in touch with Dana at ProBuilt Automatics. He'll custom tailor a TransGo kit for your application. I'd also suggest installing the Vette servo to firm up your shifts. Dana provides awesome tech support as well. He'll spend as much time as you need on the phone and walk you through the installation step by step if needed. Here's a link for Dana. http://www.700r4l60e.com/

Sorry..... had a bad day. just caught me wrong. I know what you ment,I had to work behind "those people". The guy I bought my 88 from took off the air tubes and tried to force cource thread carrage bolts in the manifolds, painted the back glass because he couldnt afford to pay someone two tint windows anda whole slew of other "What the heck was this guy thinking" things done to the car. But thats another story

i just did the swap from a 2.73 open to a 3.23 LSD

its well worth it, better off the line, better 60-100 better all around. plus a good cruise RMP

highly recomend

Hey 89rs, how long did it take you to do the swap? any complications?
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pat hall, that is exactly the way i drive my car! thanks for the links.

way to long, lol..... nothing went right, parts were ordered wrong the guy puttin it together had to do it twice, infact i got to take it back to him because the gears are whineing

all in all its easy, took me no time to remove it from the car, installing it was pretty easy to, a good freind to help makes it a lot better...... all you need is a good jack and good set of tools, you can do the swap with the rear in the car to.........i had to swap axles because my pinion blew out the side of my old one

now all i got left is to correct the speedo gears

you just swapped the gears then? I was planning on changing out the entire axle.

Lets see. My car came with 2.73 open diff. I swapped out that rear for 3.42s, noticed a good bit more pickup, but it sounded like the engine was screaming while on the highway. Drove it around like that for a while, until I finnally got tired of the high RPMs on the highway, and the milage sucked too (also had some issue with the trq converter lockup). So I swapped the 3.42s out for 3.23s. I think this is a much better chioce for all around driving. The converter lockup acts normal, RPMs are better at highway, and it's still feels better off the line than with the 2.73s.

Just my

no i got a whole nother axle, a brand new auburn pro serries LSD (i wanted a eaton but didnt want to wait an extra 2 weeks for back order), new seals, new bearings, 26 spline axles, UMI LCA's, UMI panhard, Z28 sway bars, energy bushings, and the 3.23's

if you get lucky and find a good low mile 3.23 LSD rear end then just swap them, but i basicly got a axle housing and totaly put new guts in it

If you bought all new "guts" for it, any reason why you bought stuff that uses 26 splines instead of 28 splines?

Question guys... i seen a guy on craigslist advertising that he has upgraded rear end posi gears for sale.. i believe 3.73-4.11 etc.. ARE THEY HARD TO INSTALL/REPLACE my current ones???

It's easy to swap out the whole rear end assembly, but to swap out just the gears is hard. Plus you need special tools.

26 spline is cheaper
plus i never understood how more splines can be stronger, to me less slpines means more meat for it to grab........but IDK

id like a better explanation on why more splines is stronger

My car originally came with 2.73s and the previous owner had installed 3.42s. I hated it on the highway as well. I chose a similar route (bw 3.27 posi) and liked the rpms on the highway but not the fact the posi was on its way out. Now its almost finished and put back together.

89RS: I know this is an over simplification and someone can probably offer a better explanation from an engineering perspective. But, think of it taking a certain amount of torque to shear (ie. strip or break) a single spline. With each additional spline, more torque is required to shear them. Plus, you need to strip them all at once - you can't just strip one spline. I don't know if the equation is linear (each spline adds a fixed amount to the torque limits) or if it's some kind of curve (the torque limit increases by more than the limit of a single spline).

For a simple example (taking the linear eq approach), let's say it takes 20 ft lbs to shear one spline. If you have 26 splines it would take (20 x 26) 520 ft lbs of torque to shear them. But, if you had 28 splines the limit would increase to (20 x 28) 560 ft lbs.

Hope that helps.

Ok guys i've got 2.73 and i want to upgrade to 3.23 but as it is i get about 10mpg, i know yall said that they increase the gas mileage for city driving but how much does it affect the highway miles?

Only 10 MPG

Foot on the floor 24/7? jk. There is something goin on there. You should be in the high teens low 20s if that is a tuned port 350.

no joke, its a carbed 350 outta an 87 c10 pickup (orginally fuel injected) with an edlebrock 1406, edlebrock intake, a mild cam (don't know the specs), and some kind of headers. i think they mighta hacked somethin up to fit the carb but idk
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nope carb

Not to mention what 89IROCZ28 already explained, I was damn surprised at how much thicker the 28 spline axles are. I put a Torsen in an 85 rear that had the 26 spline axles originally, so I had to replace them with 28 spline to fit the Torsen. I never bought much into the 26 vs. 28 theory myself, until I compared each axle side by side. The 28 is substantially thicker where the smooth part of the axle transitions into the splines! Mind you, this was a stock, used set of 28's as well, not aftermarket replacement ones. I don't think 2 additional splines really matter a whole lot, but the difference in overall thickness, or diameter of the axle shaft itself really surprised me. I've never really heard of anyone actually breaking a 26 spline shaft, but the extra thickness of the 28's is reassuring. Btw, I have to agree with KrisB on 3.23's. I also ran 3.42's for a while, then dropped back down to 3.23's, and I've been way happy with them for overall driveability. I would've kept the 3.42, but it was a pegleg, drum rear, and the 3.23 rear I picked up is a posi with PBR discs, so the choice was obvious there!

Nah dude, you were justified in letting me have it. Lol. I reread that post and I did come off as pretty arrogant. I feel your pain on finding such silly crap being done to your car from a previous owner. Some of the things I've seen over the years make me wonder how some people even manage to tie their shoes in the morning, let alone work on a car!

the car moves fast through the gears. its not good for a daily driver or highway driving.
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not sure what im going to do with them when i get them out. ill post it if i sell them

yea makes some more sence, i was on the thought that the more splines the smaller each spline would be there.......etc etc

im not to worried about it, it aint like its a drag strip cap with 500HP...... all the 26 spline stuff was alot cheaper, and like said, i really never heard of anyone breaking one, unless the have a radical engine

ok so i wanted some 4.10's until i read this thread. i dont really care about highway stuff too much as my car is mostly an around town and saturday night car. plus i'm starting to get geared up for autocross stuff. anywho, does anybody know what rpm/speed they had on the highway with various gear sets. i dont know what my car has but i definitely want more pick up. i remember the last street stock i built it was like night and day with gears. it turned a bottom five car into a top three car lickity split. course i went from 2.73's to 5.13's. blah blah blah... anyway my car is an 89RS 5.0 tbi with a trans kit and pretty much no other mods. what kind of top end should i expect with 4.11's or 10's whichever?? and why would yall recommemd a gear such as 3.42??

I was running 4.10 with a 700R4 with a steel drive shaft. When I was on the interstate running 70mph I was taching 3000rpm, anything over that I felt i was getting a a very fine driveline viberation. I had new tires, u joints and the viberation was never there with the stock 2.73's. The only thing I could figure was I was over spinning the driveshaft since with an OD transmission you never really get a true 1-1 ratio like you would with a manual OD. I will be switching out my 4.10's for 3.73's shortly.

wow that somes really high with the overdrive and all huh?? did you have any work done on your trans?and also, how do i know what size to get. i do not plan on doing the install but i could def. save some money buying them myself and having a shop install them.

No I had no work done to the trans at all with over 150,000 miles on it. One of the problems is first gear is it feels like a dump truck in granny low since the 700R4 has a 3.09 first gear. When i bought new tires I got a very very soft compound which I thought would help with traction on starts from a dig. WRONG traction is a major issue.