canabait

I have a76 (former L-48 current 383) W/ 3.08 gears and a turbo 350 trans. I remember some posts which gave some formuls w/gear ratios and transmissions & rpm @ 60 mph. Can anyone help me find that info? Thinking of 3.55 0r 3.73 gears and may or may not go to a 700 R4 Thanks for your help.

pawpaws toy

http://tri-5.chevyrides.com/speedo.php

silver79

Go for the 700R best thing with 3.55 I roll at 2100 rmp at 70MPH way better way to drive, you can actually speak to someone in the car.

Vette5.5

While not a Vette, have a car on 255/60/15's, 3.73 axle and 700R4 lock up. 70 mph's about 2400 rpm. Figure a TH350 to be more like 3500 rpm, especially with no converter lock up. Guess you can see why 700R4's are so popular.

Ironcross

My gears of choice and factory are 4.1 and 4.56.....I double the tach reading with the 4.1`s, 3500 reads 70 MPh and the 4.56 gear is spinning 4000 at 70 MPH......other than those gears I don't know....I never used any formulas, just observed the tach at those RPM`s with the OE size tires.....

JohnnyLT1Runner

I have 3.73's in the 79, it turns 2500 at 70 with a TH350.
For contrast, I have 4.10's in my 94 Z28 and it is at 3500 at 70 with a 4L60E.

thegazman

If you have a 3:73 differential and TH350 you have to be turning more than 2500 rpm's at 70 mph.

7T1vette

Unless you go with some really wide/sticky back tires, you don't want to go much steeper than a 3.55 rear gear with the auto tranny. With the torque multiplication of the torque converter at take-off, you will just create a bunch of smoke. And, you will defeat the benefits of an overdrive tranny when you drive it on the highway.

If you are a 100% or very serious drag race guy/gal, steeper may still be better. But, if you drive it on the highway, you will be running around 2600-2700 rpm at 70mph, rather than at 2200 with a 3.55 gear.

JohnnyLT1Runner

Correct.
It doesn't sound right to me, but I don't know what the final drive ratio in the trans is, nor can I really confirm that the gears are actually 3.73's. The speedometer is 10 MPH faster than what it really is going, and that difference is what makes me think that. Unless the stock gears were absurdly small, like a 2.73 or something, and were changed to 3.23's. That is more likely though.