I have a convertible 1971 oldsmobile cutlass supreme. The engine is a 350 and the car has a 3 speed hurst shifter. I'm putting a 8.5 10 bolt posi rear end with mosier axles in the car. the tire size is 235 60/14. I have the choice of 3.08 gears or 3.42 gears. Based on the information given (I hope it's enough information) which gears would be a better setup. I think my engine pushes out 360 to 380 hp. I want to be fast off the line but I don't want to be screaming doing 75 on the freeway. Thanks in advance for your help!

 

3.42 is my vote

 

http://www.angelfire.com/fl/procrastination/rear.html

This program will show you your engine rpm once you plug-in the other information.

It helped me when I was pondering like circumstances.

 

If you cruise freeways a lot you won't like 3:42's.

 

Put 3.42s in it & move up to a 15" rim with a taller tire. 14" tires are for show cars not for drivers.

 

I put 3.42 in mine and am glad I did.

 

I have 3:42 with 295/50/15 tires. When doing 70mph the engine will spin 3000rpm. It's not that bad once you get used to it. I would definetly recommend 3:42.

 

I've got 3.08 in mine and I'm going with a lower gear soon, just haven't decided, was thinking right around a 3.50. Kinda depends on what's available for a 12 bolt.

 

[QUOTE=hilbily;738472]I've got 3.08 in mine and I'm going with a lower gear soon, just haven't decided, was thinking right around a 3.50. Kinda depends on what's available for a 12 bolt.[/QUOTE


Chevy 12 bolt has 3.31s & 3.55s available. Olds 12 bolt uses 3.42s.

 

If you engine actually pushes out 360-380, you've got more than 300 ponies at the wheels. The torque number has to be right there too. I don't think you need the 3.42. Might have trouble keeping traction.

I've got 3.23's in the rear, and at 80 she's turning loud. But mines a stock build, your 350 is nowhere near stock.

How often are you on the highway? Once a week in the good weather, once a month? 2x a season? That's the major factor. If you rarely travel on the highway, or do so very infrequently, I wouldn't worry, it'd get the 3.42

 

3.42 is want i'd go with. I have 3.73's and haven't seen a highway in 20 years.

 

you can say that again!

 

I've got a 3.23 posi in my 73 442 and do a fair amount of highway driving. It's turning close to 3,000 rpm at 75 mph which is enough engine noise for me on extended trips.

I agree with the others if you do alot of highway driving I would not put 3.42's in your car. I'd stick with a 3.23 or a 3.08 gear ratio. If your goal is more performance and most of your driving is city streets and rarely highway, then go with the 3.42 gears.