I have a 1969 396 SS, the car had the rear replaced some time ago and has a 411 rearend that I'd like to replace with something geared a little higher.. Does anyone have suggestion as to which gear ratio would be best ? it has a 4 spd M21 ... 15 inch tires .. Thanks.

Welcome JFK ! You certainly have your work cut out for you living up to that screen name!;) What is your car normally used for? If it's mostly for street use, my guess would be something along the lines of 3:42 or 3:23. They dont make the 3:31's anymore, but there are plenty of used ones for sale. What are your engine specs? That plays a lot in your selection as well. John (what's ur first name? If it's John, it really gonna freak me out)

Thanks John... Name is Joe .. normal car use will be city / highway
mostly speeds in the 40 to 60 range.. As for the engine spec???? Not sure
what info you were asking for... I'd like to keep the engine in the 2000 RPM range if possible.. Thanks for replying.

I have a 69 SS 396/325 with a 400 auto trans. It has 3:31 gears and runs 3000 rpms at 70 mph. I run a stock 14" rim with BF Goodrich tires. I can't remember the size of tires off the top of my head, but they are pretty close to the stock diameter. If your running a bigger tire (diameter) with a 3:31 gear your rpms should drop a little lower than my numbers.

Thanks Ray, my is 396/375 4spd and with the current rear-end it's turning 3200 rpms @ 50mph.... Too high for me

If you want to bring the rpms down more than what I have, look into a 3:08.
I like my 3:31's, pretty good on take off and cruises great around 50 mph. Like John said. they don't make 3:31's but you see them posted for sale here once in awhile. Good luck on your choice.