Gear question

[comet_666]

I currently have an 8 3/4 with 742 case with 3.91 gears (69 Charger). I am currently running 26 inch tires but I want to be able to not be turning 3500 +rpm on the expressway at 70. The motor is a 512 stroker which should be putting out about 550hp / 600+ tq. My builder suggested 3.23 gears but I still want to have that punch off the line..so yes the best of both worlds I guess. He is suggesting an ATI PHASE 4
3.70 - 4.30 Rear Gear converter and says if I switch the gears down the road to 3.23 then I should be able to keep the sanme converter.
My question is should I take his suggestion and go with the 3.23 or go for something like 3.55? Also if I change the gears out should I just buy the gears or buy a 489 center section?

Thanks all!

[Sublime/Sixpack]

I'd go with 3.23 ratio if it were mine.

[cdr]

I took my 3.91 out & went to 3.23, 512 ci does not need a 3.91 gear on the street. with 3.23 it is still violent ,I love it 

[crj1968]

I'd go with the 3.23's also. With 550HP I dont think punch off the line will be an issue, especially with the right converter.   

I also dont see any reason the ditch the 742 case, unless I'm missing something?

[comet_666]

Wow, thanks for the advice guys!
Any recommendations where I could actually order the gears from?

[comet_666]

http://www.ringpinion.com/b2c/ProductDetails.aspx?ProdID=12127&Product=YG_C8.42-323&Brand=Yukon_Gear_Ring_and_Pinion_Sets&ShowAA=True&Year=1969&Model=Charger&DriveType=Rear%20Diff%20-%20RWD&DiffId=107&Source=DiffWizard



http://www.doctordiff.com/8-3-4-ring-and-pinion.html



I assume a 42 housing means 742?

[Sublime/Sixpack]

I'd look around for a good complete 3.23 geared sure-grip third member rather than buying/installing new gears in your existing unit. Gives you the option of hanging onto the 3.91 unit or selling it to recoup the cost of the 3.23 unit. It's nice to have options.