I've had numerous people warn me about upgrading gears on my car with the 700R4. Most people said that driving with 3.91 gears would be like driving without overdrive well it turns out my car would not drive much different with the different corvette gears, here is just a comparison of the gear ratios verses rpm. What gear ratio would you guys go with?

This is at 80MPH with a 700R4 overdrive which is .70 4th gear ratio and with the torque converter locked up and a 25.7" tall tire (315/35/17) a 335/35/17 tire would reduce rpm by about 50 rpm.
3.07 gear/ 2248rpm (this is what I have now)
3.55 gear/ 2600rpm
3.73 gear/ 2730rpm
3.91 gear/ 2863rpm (this is what I am going to have)

My engine makes good power from 2200 rpm up past 6000 rpm, I drive my car 125 miles a day but I am going to go with 3.91 gears because it should be much quicker due to more torque to the rear wheels with the bigger gear. I think I can live with 2863 rpm on the highway at 80mph. What do you guys think?

 

my vote still goes for the 3.90 gears and 70mph+no speeding tickets you cant afford to pay for you speedyspeedster!

 

Hey Chris, just to amuze you this is the rpm's at 70 MPH.
3.07 gear 1967rpm
3.55 gear 2274rpm
3.73 gear 2390rpm
3.91 gear 2505rpm

At 70mph 2505rpm doesn't seem to bad either, 3.91 might actually be better gas mileage than the 3.07 gear because my cam doesn't make much power under 2000 rpm.

 

on the street a 3.55 or 3.73 would be 100 times better. However at the track the 3.90 would be fine. Just make sure you arent shifting to OD at the track with a 3.90. If you are really shifting at 6000 (non TPI intake) you would be fine.

 

Why not use OD? I'm thinking I might need 4th gear after my swap. (4L60E)

 

The reason most people wouldn't want to shift into overdrive in the 1/4 is because overdrive is not meant to take the abuse like 1st, 2nd and 3rd. I realized this when I rebuilt my trans that the stock overdrive clutches etc. were pretty weak. I won't need to use overdrive in the 1/4 unless I am trapping speeds above 120mph, if that was the case then I would use overdrive.

 

actually its because its less than a 1:1 ratio. It will slow you down on the top end... not to mention OD isnt ment for that.

 

no he wont be shifting at 6000 either. more like 63-6600 Id say. you'll have to see what it does at the track to see where it does best, but that cam has a good powerband and the rest of your combo will support even higher rpm. even if it did better shifting at 6000, he could shift at 6000 1 and 2, then let 3rd gear rev up a little higher before crossing the finish line.