I had a 3.42 open rearend in my Z28 and the car worked very good. It came off the line amazing and I have even taken out 5.0 mustangs. The car launched well with little or no wheel spin. I switched to a set of 3.73's and an auburn posi and all I can say is hold the hell on when you punch it. The irony of it is if I launch the same as I used to i spin like there is no tomorrow. The car will do an awesome burn out and I am even getting second now. The licker is my gas milage got better LMAO. I find the car drives a lot better because it isn't pulling that stupid hunting though gears crap. I have to say I am very impressed with the change. I still like the highway feel of the 3.42's but I love taking off with the 3.73's and they are great for city driving.

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91 Z28 Camaro
305 TPI
Flowmaster 3" exhaust
700R4 with 2000 Stall and shift kit
Auburn Posi with 3.73 gears "YEEEEEHAAAAA"
Autometer shiftlight tach and B&M mega shifter
One sweet sounding system

 

The reason you spin the tires is because you have increased the amount of torque your rear tires see. I went from 2:77's to 3:73 and love it, the highway does suck though. Do you get a bad vibration above 85 MPH?

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• 89 Formula 305 WS6
  SFC's, LCA's, Air Foil
  Spohn Panhard Bar
  Flowmaster Cat Back, Tranny Cooler
  A/F Ratio Meter (not a mod but it sure spurs interest)
  Trans Temp Gauge
  Most "Free" Mods
  3:73, Zexel Torsion Posi
• 90 Eagle Talon 2.0
  (Winter Beater)
  Mods? Um, no

 

Yes i get a very bad vibration about 85 and it gets worse when i let off the gas after acceleration, whats that from??
Cody

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Wieand blown 87 camaro

 

I have the vibration too. It is from the drive shaft from what I have heard. You can get it balanced or you could by an aluminum one.

I know about the whole changing ratios and making it spin easier but I didn't go from a 2.73 to a 3.73. I only made a slight change and the traction difference was incredible. I kinda wish I still had the 3.42's because of the street ability. Good highway mileage and decent takeoff with no tire spin. My old 305 works very good for what it is.

 

its becase you have both whels spinning and not just one form the start. If you have the stock rear suspension that would be why. it cant handle posi rears very well.. better upgrade the suspension to handle that power.

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91 camaro RS
- 305 TBI
Mods: Performer TBI intake, 1" TBI spacer, K+N, jet fan switch ,160 thermo,Accel control module, Jet Stage 2 chip, edelbrock TES headers, Compleate 3" Flowmaster exhaust, Edelbrock springs, KYB struts and shocks, 700R4 built by TSI, SLP tq converter, b+m trans cooler, white guage faces, megashifter..
next month: spohn LCA's and panhard rod, BMR relocation brackets, 323 gear, lt1 cam , 350 heads

 

I am definitely ging to have to do some suspension mods but I think I am done spending money on it this year. I am all pissed at it because I have owned it for a year and a half and I haven't driven it for a month straight and not broken something. It is always something stupid and really expensive. I think I am just going to put it away, sell my truck and buy a brand new 4 banger!!!

 

As far as the vibration goes. I read that with 3:73's @ 92 MPH the drive shaft is at half its terminal velocity.. that could be why. I had my driveshaft balanced and it didn't make a lick of difference.. well except for making my wallet $85 lighter!

 

I didn't think they installed 3.42s with an automatic. In fact, my 1991 shop manual doesn't show a "speedo drive/driven gear combo" for 3.42s with an automatic.

[This message has been edited by Glenn91L98GTA (edited July 06, 2001).]

 

Yeah, 91 305 auto's came with 2.73's and posi. Well, mine did.

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-Jason M. 1991 Camaro Z28

 

My 85 iroc has 3.42's with an auto. I'm also wanting to switch gears and put a posi in but have no clue what rear I have or what posi I need. I'm thinking either 3.73's or 3.90's if they make it for my rear.Anyone have any sugestions or info for me? Thanks

 

i was told your mileage goes up if the majority of your driving is city or stop/go, because the engine doesn't have to work as hard to accelerate [when you have numerically higher gears]. makes sense to me.

 

The stock driveshafts in our cars are POS's. I forget the actual critical and half-critical speed, but an aftermarket aluminum shaft is al least twice as good.



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89 RS 350 TBI auto Hooker SC/LT headers Open element 3in K&N CVT protorque mini-starter

Daily driver 91 RS auto LO3 63k

New project- 89 Formula 350 WS6
383 or 400 to come!