Hi all,

I have a '71 Cutlass Supreme ragtop that I would like to upgrade the rearend with.

Its a 10 bolt that is open. I'm sitting at around 360 hp with the motor , but it just doesn't hava a lot of snap off the line. Pulls like a damn on the highway.

I would like to go to posi and more umph, but still highway drivable.

Your thoughts ?

 

Would you happen to know the gear ratio currently? Im going to assume you have 2.xx gears and a 3-speed.

If my assumptions are correct, then a think 3.08's-3.23's gears are the sweet spot for highway and street!

Ed

 

Yes it's a TH350 and I can only imagine that the rear end ratio is in the 2's . The car is currently in storage.

 

hmm, i do agree that the 3.23 gear ratio is a good one. But don't overlook the 3.55 gear. Gives a little more lower end torque response for a snappy start off the line, yet retains a good amount of drive-ability on the highway.

Myself speaking, my 67 442's 400 BB motor currently has a 4.33 rear-end gear ( stock from the NC Dealer) to go through. Great for blasting off the line with, but I can't drive it on the highway.

Anyhow, just my own humble opinion. Good luck with the project.

desert442

 

Do you mean "Dealer installed" or "as optioned" and purchased from the Dealer?

I have 4.30 and 4.56 in my Coupes. I do not have any problems at 65 miles per hour.

Norm

 

What RPM's are you guys getting at 65-75 miles per hour? I have a TH400 and my third gear is a 1:1 so it would seem that my RPMs would be a lil high. I haven;t been able to ID my rear but I think its a 3.42. Its a stock 12 bolt 68 442 rear.

 

What do you cars redline at ?

 

Depends on your definition of "redline".

For my 437, it might be anything from 5400 (peak HP) to 7000+ (where I think it will break) RPM.

Norm

 

I will be installing a 3:23 geared O rear....just waiting for the snow to melt I can't wait to replace the 2:56 open rear.

I have it figured to up the rpms by about 600. From 22-2300 to 2800rpm or there abouts, at highway speed.

Don't forget your speedometer reading. You"ll need a new driven gear at the tranny. In my case, a 29 tooth.

 

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

Norm