Question: What is the axle ratio of my 1993 C4 ?

[LastOfTheV8's]

How can I discover which axle was fitted by GM into my 1993 auto C4? I believe there were several options available at the time, I am just curious! I want to run her over the quarter mile at Santa Pod in England next year and naturally wish to compare her with her peers

 

[Tom Maine]

At the top of the CAC is a specs page. 1993 auto shows a 2:59for the auto transmission.

 

[toptechx6]

As Tom indicated the stock gear ratio for 93's with A4 transmission is 2.59, there was a "performance axle ratio" available as an option. Check the RPO codes on the underside of the center console lid then compare yours to those in this link, codes with letter "G" prefix will specify the ratio installed from the factory.

Corvette Action Center | Tech Center | Regular Production Options - 1984 - 1996 Corvette

If you suspect the gears have been changed jack up the rear of the car and support it safely, put a chalk mark on the driveshaft, with the transmission in neutral rotate the wheels one complete revolution while counting the driveshaft revolutions, that will verify the installed ratio.

 

[vetteoz]

1993 auto shows a 2:59for the auto transmission.

All auto C4 coupe's came std with 2.59
If you have G92 on your RPO label then you have the optional performance ratio
( 3.07 ;only one ever offered for a auto coupe ) ; RPO option G44

 

[LastOfTheV8's]

At the top of the CAC is a specs page. 1993 auto shows a 2:59for the auto transmission.

So it does, thank you

As Tom indicated the stock gear ratio for 93's with A4 transmission is 2.59, there was a "performance axle ratio" available as an option. Check the RPO codes on the underside of the center console lid then compare yours to those in this link, codes with letter "G" prefix will specify the ratio installed from the factory.

Corvette Action Center | Tech Center | Regular Production Options - 1984 - 1996 Corvette

If you suspect the gears have been changed jack up the rear of the car and support it safely, put a chalk mark on the driveshaft, with the transmission in neutral rotate the wheels one complete revolution while counting the driveshaft revolutions, that will verify the installed ratio.

Great info thank you!

All auto C4 coupe's came std with 2.59
If you have G92 on your RPO label then you have the optional performance ratio
( 3.07 ;only one ever offered for a auto coupe ) ; RPO option G44

Thanks. Its safe to assume that the 2.59 axle ratio was designed/installled with fuel economy in mind, right? Though what are the characteristics of higher ratios in comparison? In terms of acceleration, torque, reliability, driveability, durability and anything else that is relevant??

 

[surfer93]

Yes, the 2.59 and the earlier 2.73 are there for fuel economy. Which makes them turtles off the line.

 

[LastOfTheV8's]

Yes, the 2.59 and the earlier 2.73 are there for fuel economy. Which makes them turtles off the line.

I guess that explains why I read somewhere in here 'Real vettes are manuals!' Still love my automatic turtle to death though

 

[vetteoz]

Though what are the characteristics of higher ratios in comparison? In terms of acceleration, torque, reliability, driveability, durability and anything else that is relevant??

Depends what you are after, 3.07 is a great kick in the butt improvement without affecting fuel economy.Would put a smile on your face
Many auto LT1 owners go to 3.54 or even 3.73 if they have engine mods.Remember; you still have the O/d 4th gear which brings your cruising revs down

 

[Rogue]

I have the 3.07 and it rocks! Great power off the line and not too revvy in the highway.

 

[LastOfTheV8's]

Yes, the 2.59 and the earlier 2.73 are there for fuel economy. Which makes them turtles off the line.

I have the 3.07 and it rocks! Great power off the line and not too revvy in the highway.

I suddenly wish I had that one installed.. would the torque converter engage at a different speed by any chance? In mine it seems to engage at 42mph (68kmh)
Have you run your 91 on the dragstrip? I am wondering how the better axle ratio would affect 60ft times, and ET ?? Presumably trap speed would be the same as mine? (within reason!)

 

[Towu4free]

my 94 conv has 3:07 ratio and its an auto

 

[vetteoz]

my 94 conv has 3:07 ratio and its an auto

Was a option on any auto so you will have G92
" performance gear ratio"
on your RPO label

 

[vetteoz]

. would the torque converter engage at a different speed by any chance? In mine it seems to engage at 42mph (68kmh)

What what I have seen in the programming, lockup is at the same speed; there are no differences in the tune in relation to the diff ratio

 

[kim]

If your not the original owner you cant always go by the code you have, the last owners may have put diff. gears in it. My code is GM1 but I thaik the gears were changed because it takes off like a bat outta hell.

 

[vetteoz]

I thaik the gears were changed because it takes off like a bat outta hell.

Jack rear of car , put chalk mark on driveshaft and tire.
Rotate wheel and see how many times the wheel goes around to get one turn of driveshaft.
That is your ballpark rear end ratio
2 1/2 turns =2.59
3 + a bit = 3.07
3 1/2 turns = 3.45 / 3.54

 

[surfer93]

Curious that the 3.31 went by the wayside, seems like that would give you great take off ability and pretty good gas mileage.
I just went to 3.07, take off is better, not great and the gas mileage went down from about 31 hwy to 29, cant really tell if around town mileage went down or not.

 

[G Winter]

Curious that the 3.31 went by the wayside, seems like that would give you great take off ability and pretty good gas mileage.
I just went to 3.07, take off is better, not great and the gas mileage went down from about 31 hwy to 29, cant really tell if around town mileage went down or not.

My 90 with 6 sp has 3.33 gears. Great takeoff, actually have to be ready real quick to go to second if you jump on it hard.You don't spend much time in 1st.
This is in a Dana 44.
Glenn

 

[Roadster Guy]

My LT4 has the stock 3:45...Lots of jump in 1st (and 2nd and...)
RG

 

[SilverFoxDan]

Reversed?

Jack rear of car , put chalk mark on driveshaft and tire.
Rotate wheel and see how many times the wheel goes around to get one turn of driveshaft.
That is your ballpark rear end ratio
2 1/2 turns =2.59
3 + a bit = 3.07
3 1/2 turns = 3.45 / 3.54

I believe it is the other way around. The drive shaft always, always turns faster than the drive wheels. I set up my '65 GTO for the strip with a 4:11 rear end (drive shaft spins a little over four times for each revolution of the rear tire). This gives you amazing, head snapping, torque to the rear axle but the speed tops out quickly as you hit your red-line much faster.

If the drive shaft turns slower (one revolution for 2.59 revs of the drive tires) the C4 Corvette would be capable of hitting about 1,000 MPH at red line. (Waxed, tail wind and going down a 70' hill)

 

[kpic]

SFD

If it is a locking or posi axle:
Lift both tires off the group. Turn wheel 1 complete turn.
-Count the turns of the drive shaft.

Non-posi or peg-leg:
Lift the tires off the ground. Turn the wheel 2 complete turns.
-Count the turns of the drive shaft.

With a peg-leg diff you really don't need to lift both tires; however it is easier to get underneath.

PS:
This method will not work well on a posi that is worn out as the wheels may not rotate equally.