I was just curious how I can tell what kind of gear ratio i currently have.. i was thinking of of upgrading as i want to make the car quicker.. i have a truck taht i use in the winter but want to make this a nice summer car taht can be used daily however i also would like to race with it.. so just wondering how i can find out what i currently have in the car.. it is a 1987 Chevy Camaro Iroc-Z that came factory with a 305 however previous owner put in a 350... also by upgrading the gear ratio would i have to upgrade the trans? is there a way to tell what kind of trans i have?

 

take the cover of the diff. there is two numbers on the gear divide them. i just boughta 93 z rear end the numbers were 11 41 divide the to you get 3.72.. witch is 3.73 gears... you shouldnt have to do anything to the trans except speedo gear if you want to have an accurate speed im not shure how to tell what trans you have

 

if i take the cover off wont all the fluid come out? - also is there a limit to what gears will just go in.. i was thinking of doing 3.73.. i was thinking 4.11's but a lot of people said that 4.11 will proably not be good for a street/daily driver.. but they said that the 3.73's are good.. so does it matter what i have in the car now? also whats the install like on changin the gears?

 

well 4.11 will not be good on a dd because your car will be screamin at low speeds i was only going to go to 3.42 until i got a sweet deal but yes fluid will come out so you might as well change the fluid the swap isnt that hard im 16 and ive only seen it done a couple times and i did mine in about 3 hours. but if you dont know what your doin then you should find a buddy that does or someone than can help i dont think it really matters of what gears you got now but 342 or 373 are the way to go it will feel like a totally new car

 

Do you still have the white label in the console? Thats the RPO sheet. There are 3-didgit numbers/letters there that coinside with GMs RPO sheets.
G__ are gear ratios. Like GT4, GU4, GU6, etc. If theres a G80 along with it, then you have a locker/limited slip unit as well. If not, its a peg-leg or one wheel pull.
A 305/auto was stock and if its a stock rear. Most likely its beween a 2.73-3.42.
You could try to calculate it with an online ratio calc. You need to do 60MPH (or a steady cruising speed in top gear) and record the RPM's you are at. That would get you close to what it is.

http://www.csgnetwork.com/rearendgearcalc.html

Manipulate that calculator.

 

FYI, a 3.42 would be good all around if you do highway or interstate as well as in town drives. The 700R4 has a 3.08 1st gear. And with a 3.42 rear, it will be very snappy off the line. Yet maintain a decent cruising RPM in 4th (the lockup converter will also help).
The 3.73 will have very good off-line response and carry to the midrange well. But will sacrifice cruising RPMs and have less milage on the highway.
IDK what cam you have and whatnot. If you had a stock 350TPI and cruised with it, a 3.42 would be best. The TPI is torquey and midrange. If you are cruising at 60MPH with a 3.73 and already doing a high RPM, then when you punch it into 3rd and try to pass, your powerband may be at its end and you wont have great upper-end response like you did on the low-end with the 3.73's
In other words, dont over gear it to how you drive/where you drive/etc.

 

Here's how to determine what ratio the rear is (jerk the diff cover and look--no doubt the fluid needs changing as well as the limit slip additive if that's what you have): numbers are stamped on the ring and pinion:

41 : 15 = 2.73
41 : 14 = 2.93
40 : 13 = 3.08
42 : 13 = 3.23
41 : 12 = 3.42
41 : 11 = 3.73

If the trans is auto, it's a 700R4. Manual, T-5. You may have to swap out the driven and/or drive gears in order to make the speedo read correctly.

JamesC

 

when u do the gears make sure u get the right carrier number related gears for it if its say 2.73 and u want 3.73 u have to make sure u get the right gear set for that specific carrier either a 2 or 3 carrier

 

what do you mean 2 or 3 carrier? how can i tell?

 

3.08's down, series 2; 3.23's up, series 3.

JamesC

 

oh ok.. now saw my car came stock with 2.73 or something like that which would be a 2 carrier but then i wanted to go 3.73 which is a 3 carrier what mods would need to be done?

 

No need to pull the cover, drain the fluid or anything that "drastic".

Jack the rear tires off the ground. Put the tranny in Neutral. Spin a tire, by hand, 1 revolution & count the # of times the pinion rotates. You'll be able to tell what you have that way.

You'll get something like a 3 1/4 turns. On a 9 bolt, it'll be 3.27.
3 3/4 turns, on a 10 bolt, will give 3.73s.
4 turns, on a 10-bolt, is a 4.10, etc.

Just count the revolutions and look at the available gear ratios for 9 & 10 bolts, depending on which rear you have, and you'll know with a lot less work or mess of puling the cover.

 

Read through the following link:

https://www.thirdgen.org/forums/tran...eries+3+series

JamesC

 

X2. Aftermarket gears come specific for the type carrier. So say Richmond makes 3.73s for bot a 2 and 3 series carrier.

 

so i did the little test where you turn the wheel and watch rotations.. i calculated that the pinion rotates just under 3.5 times.. I also have a 10 bolt.. so i assume this means i have the 3.42 gears right? would it be even worthe the upgrade to 3.73?

 

3.23/3.27/3.42 gears are probably the best choice around, for the acceleration & highway use.

I had 3.73s on a T5....Even with the 5th gear, I noticed the MPG drop & RPM rise at cruising speed

Such a small increase wouldn't be much of a difference for you (3.42 to 3.73), to really justify the cost. 3.08 open to 3.73 posi was my incentive...Or rather, my WIFE'S decision to "upgrade".

 

sounds to me like you did this wrong. You have to spin the wheel X number of times, and keep track of how many times the driveshaft rotates. Then divide those two numbers together to get the ratio.

 

He did it right...He said the PINION (which would be the same as counting the driveshaft) rotated just under 3.5 times)....What he left out was ".....in 1 full turn of the wheel."

 

Thanks Miks86TA I still got the sheet and saw the G80 on it.