[AscotBlue'71]

Getting ready to R&R the 12 bolt for my '71 SS the original set up is a 2:73 open rear. I've decided to use an Eaton posi carrier, but havent nailed down which ratio i want to go with yet. i am considering either 3:42 or a 3:55 ratio. The motor and trans are a little warmer than stock '71 402 w/ a TH400. I would like a good performer to play with on the street but dont want to wind the BB high in the RPM's when going 70-75 on the highway like a 3:73 does. What gear would you go with?

 

[MEJ1990TM]

Unless you've got some ridiculous cam I'd go with the 3.42's. I've never driven a car with anything lower than 3.31's. But I really like how those 3.31's work. The right balance between highway RPM and get up and go. Overall though I don't think you would notice a huge difference either way.

 

[mr 4 speed]

X2 on the 3.42
great all around gear.

 

[fleming23]

Looks like I am in a very similar situation as you. I think I have decided on a 3.42 over the 3.55 for the same reasons mentioned above. The difference between the 2 is marginal. Right now I have to convince myself to splurge on a rebuilt 12 bolt vs adding a powertrax to my 10 bolt 2.73.

 

[Euell Florett]

You would enjoy using a gear ratio calculator. :yes:

Available free on-line...just GOOGLE. :beers:

 

[AscotBlue'71]

WOW!!! Did the gear calculator and this is what it said:

3.42 @ 70 MPH w/ 235/60-R15 tires = 3082 RPM

3.73 @ 70 MPH w/ 235/60-R15 tires = 3360 RPM

Go with 3.73's????????????? would increase the fun factor :yes:

 

[Lionel-n-Chevelles]

I would go with the 3.42s.

http://www.richmondgear.com/101032.html

 

[Sergio 69 SS396]

Find some 3.31's on eBay.

I could sell you mine in May when I get my RS600. Maybe haha. I have 3.90's right now with stock 26.5" tires. At 75, I"m screaming at 3500. Kind of annoying. So I'm getting 3.31's to hold me over for my trip to San Diego. Plan to be at 3150 now if memory serves. But when I get my 5th gear, I may go back to my 3.90's. We'll see........... Keep us posted on how it works out