GrayTA

I know that a 3.42 will out accelerate a 2.73. My question though is what is a quantifiable measure of that difference.

Does anyone have time slips from when they changed their car out?

What about 0-60 times?? How much of a difference did that make?

My understanding is that it is a definite seat of the pants feeling, but just how much?

Any takers for this question?


PDG

JamesC

iTrader: (5)

Sorry no time slips, but the difference in acceleration (especially if you have some power) will put you back in the seat and make you smile like a Shakespearian fool.

JamesC

89RS_82Z

iTrader: (2)

going from 2.73 to 3.23 LSD, will post up time slips when done

Trick414

I just did mine this week. Had an open 2.73 and went to an Ebay'd Zexel Torsen 3.42 posi.

In the first few minutes while driving home from the shop, I let the engine get up to operating temp. I then made a few different trials - full stop/full throttle, running start/full throttle, etc.

At first, I was a bit underwhelmed. I had expected a huge difference. But, I only have a wimpy stock 305, so it probably isn't seeing much advantage.

With the old open 2.73, a full throttle start would kind of "wiggle" the back end. I can't really describe it. An open rear shouldn't make any difference if you have good traction to both tires. With the 305, I ALWAYS had good traction.

But, the posi definitely launched straight and true, so that was an immediate benefit I noticed on the drive home.

However, after running it around some this weekend, I can definitely say the upgrade was worth it. I'm starting to notice the subtle, but enjoyable, acceleration in all RPM ranges.

Clearly, once I start modding a bit and making more horesepower, the rear-end is going to make a huge difference.

I think if your 350 is making anymore horsepower than my stock 305, you will notice a big difference and be very happy.

slow_90firebird

So how much did a shop charge you, to install the 3.42's and the posi carrier? Or did you do it yourself?

Trick414

Jason Bailey at Texas Drivetrain Performance did it for $200.

He didn't know me prior to this, so I guess I got the going rate. I don't think I"m doing him wrong by quoting the price here.

A few other shops were twice as much.

I watched Jason do the whole procedure and he talked me through the job. He does very good quality work for all of us in North Texas.

After watching him, and hundreds of dollars (or more) in tools and presses, I think I could do the job myself. But, I think this job is best left to the professionals.

The 3.42 ring/gear and posi unit were $150 on Ebay. Jason inspected them closely, and as far as he could tell they were in good shape.

Jammin'Trey

I am putting in some 3.73s and posi in my 89 this week will let you knwo what I felt.

slow_90firebird

Damn, I wish they had deals on work like that around here in new england.

I have talked to people, and to my best guess, I would be lucky to find labor on an install like that for $500 or more!

GrayTA

Thank you all for your information here!!

Quotes for my change ranged from $315-$450. Then it turned out that noone had my rear anymore. So, its a waiting game again for me.

@Jammin' Trey - what rear do you have now? And is there any chance you might get a stopwatch and measure your 0-60 time now and post the results after your switch?


PDG

TZFBird

It is a big difference when you get that torque multiplication factored in. I went from not really being able to do a whole lot with the open 2.73 gears to lighting them up with a posi and 4.11. I still have the 305, but the transmission has been gone through.

I don't think there is any way you can be disappointed with a gear change except the decrease in gas mileage, and the fact that changing speedo gears sucks.

I got my gears setup for $40. It's all about connections!

shaolink9

I went from my stock 2.73 to a 3.42s the seat of the pants feel was there for sure. I also had a 383 at the time. A buddy said that track time are not that terribly significant but the fun factor is and to me thats the only reasson i have f-bodys :-D

gmgod

Do a search for madmax and his vert. He chronicled a few changes with dragstrip passes a few years ago. 2.73 to 3.42 gears were one of them.

Jammin'Trey

I am changing the gears myself with my dad, I am only 16. so you older guys should seariously get a buddy and do it in the garage on jackstands. I have the 3.73s ordered aswell as 3.42s with aq GM gov loc rear end.

Currently I have 2.73s and a one wheel wonder diff. Me and my bud wil time her 0-60 today.

91z 2 8

Im thinking about going 3:42s cause now that i think about it i get horrible milage now and dont want 3 73s. But do any of you know if there is a shop in PA that could do this? i dotn wanna do it my self.

gcgarner

Trey ...

STOP before you put the Gov Lok (a.k.a. Grenade Lok) in your car. Sell it and buy a good posi unit. These were meant for to help S-10 pickups pull boats out of the water (and other low-speed posi applications). If you plan on running that car hard, your rear end will inevitably blow up. Just search this forum for "Gov Lok" and see what comes up. An Auburn, Eaton (that is meant for hi-po applications), or even Zexel posi can be picked up for cheap on Ebay or sometimes in the classifieds on this site. Seriously, you don't want to have to build it again. Do yourself a favor and ditch the Gov Lock!

And I think it's cool you're doing this with your Dad ... but I hope you have the tools to do it right. Otherwise, Gov Lok, Auburn, Zexel Torsen, Detroit Locker ... it doesn't matter ... if it's not set up right it's going to go quick.

Jammin'Trey

My dad hates GM cars though... My family owns a Honda dealership up her in omaha....

He is neglectant to my camaro.

Zepher

iTrader: (1)

I've had 3.23, 3.73, 4.10's, and now 3.42's in my Formula.

3.23 to 3.73 - Dropped .5 seconds in the 1/4 (15.7-15.2) and gained a few MPH, 86-90mph (this was when the car was an auto)

3.73 to 4.10 - same ET, 15.2, but picked up another 3mph (93mph) Car was a 5 speed.

4.10 to 3.42 - Same ET, 15.2, dropped 1mph, 92mph.

60' ranged from 1.99 to 2.2 on street tires.

kerplunk318

iTrader: (3)

373s in od with the coverter locked up isnt bad at all, I got over 20 mpg goin down to the beach goin between 50 and 60 mph

stroker86

i recently put a gov lock in my '86 383 powered camaro. no problems yet. i am actually very pleased. before i had the open diff and hated it.
i have had a very good friend of mine with a fourth gen and experimented with many different posi units. he also is a drag-stip regular and pushing just shy of 400 to the ground via 7.5' 10 bolt & M6 so he broke a few (4 that i know of). anyway, out of all posi units he used, the gov loc was the best hooking unit and most enjoyable on the street. im not trying to pursuade anyone, i know that when those things go out (seen first hand), they go big. but to my knowledge, and applications so far, nothing wrong with the gov loc. ill let you know mine ever decides to explode, then i might change my decision...

stroker86

another question for you guys. a friend of mine and i looking into how-to installation video's for performance mod's on muscle cars. this would be one of the topics covered due to the volume of the modifications on all f bodies. give me some feedback on what you guys would think about a video how-to that you can watch online explaining each step as well as optional information. i would think it beats the hell out of reading a book or even online threads on installation of parts... simply watch a video

Jammin'Trey

I will use the gov loc until I can afford a new powertrax

tilerob79

hey does anybody know the speedo gears i need to get my speedometer calibrated. on a 1990 RS with 305 tbi and 3.73s with posi?
If my speedometer doesnt have a cable do i need the parts or is it all calibrated by the computer. thats what a shop down here told me and they want $345 to do it.

DM91RS

If it is electronic you might be out of luck as GM did not install the 3.73's into an electronic unit that I know of. The cable units I know they did. You could get what I had to for the 3.73's with a T5. It's one of those units you splice into the speedo cable and tune it until its correct. Mine was eazy to set up and seems to be correct.

http://www.dakotadigital.com/index.c...126/prd126.htm

HTH

JamesC

iTrader: (5)

All you require is the drive and/or driven gears. Check the sticky.

JamesC

stroker86

if its an auto, their are gears in the tailshaft of the tranny and any chevy dealer should be able to calculate what you need, just tell them the rear end ratio you have. they got it close on mine.

TZFBird

You guys forgot about BowTie Overdrives.
http://www.700r4.com/speedoCalc/speedocalc.shtml
You can get the gears for about $20-30 shipped from them. This is a link to the calculator. I can tell you this however, anything above 4.xx is not going to be very accurate. I am about 5mph off with the 4.11 gears. I got my gears from them and would be extremely pleased except for the fact that they do not offer any gears for the higher ratios.

racing geek

iTrader: (5)

So based on what Zepher posted, I should drop at least a 1/2 second off my 1/4 mile time since I'm switching from a limited slip 2.73 to a Auburn 3.73.

Does anyone know how far off the speedo would be by switching from 2.73 to 3.73?
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gcgarner

I would think about 15 mph!

GoodlookinRS

iTrader: (1)

I just got my car back yesterday from going to 2:73 to 3:73 from a dead stop not a big difference i think i need a bigger stall. But once you hit it rolling a little bit its bad. I went from 10mph and hit it went up to 3500 rpms it started to roast then went into 2nd it burned some or lol. In a way i like the shift kit and corvette servo better than the gears.
kevin

gcgarner

Shift kit is my #3 best mod to date on my car. 350 swap being #1 and headers & exhaust being #2. But SFC's & Wonderbar just went in yesterday and I haven't had a chance to drive it yet (since the rear end isn't back together yet), so the shift kit might get bumped to #4 if the SFC's and Wonderbar work like everyone says. Gears ... I might could have done without. It's not like I drag race much or anything. And they are keeping my car in the shop!

Glad to hear you got your car back, GoodlookinRS!! I know you were stressed.

GoodlookinRS

iTrader: (1)

Oh i was killing my self lol. I think once i get or you get power behind some big gears it will be bad. My next mod is a 350 made into a 383 stoker looking for around 400hp to the rear so i am hoping i will have an 11 sec car. But ya if you dont race a hole lot or anything put the shift kit in or something its really fun!
kevin

Zepher

iTrader: (1)

Really? It felt the same?
when I went from 3.23 to 3.73 when I was auto, I felt a nice increase in off the line acceleration, as well as nice acceleration in any gear while rolling.
http://www.youtube.com/watch?v=BZIeHa-LwaE

racing geek

iTrader: (5)

Was that video your 305 TPI with 3.73 rear gears? Is so, I look forward to experiencing that in my car. Were there any other mods to the car when that vid was made?

What gears would you, Zepher, recommend for autocross? Are the 3.73 gears I plan on using too much?
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Zepher

iTrader: (1)

The only mod I think at that time was the 3.73's. I can't remember if the HSR was put on before or after the T5 swap.

3.73 should be decent for the auto-x since you have the 305. The gears will substitute for the lack of torque.

for my car, 3.42 is almost perfect, there are times when I wish I had 3.73 gears since I lack a bit of low rpm torque, HSR pushed the torque band higher into the RPM. the 4.10 gears were overkill, great off the line but I would hit max rpm in 2nd gear, and there would be no time to go to 3rd and then back to 2nd.
These videos are with the 4.10 gears,
http://vids.myspace.com/index.cfm?fu...ideoID=1191222

http://vids.myspace.com/index.cfm?fu...ideoID=1191255