67 GTO Rear End Gear Ratio

I’m restoring a 67 GTO, stock 3.55 rear end too low for highway use. Looking to rebuild rear end (add posi-carrier) and would appreciate a suggested ratio and corresponding tire/wheel sizing. 400 cu” engine getting tooled to about 425hsp. Want both acceleration and 70 mph comfort (not 4K rpm). Thank you, Bill in Oregon

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Originally Posted by roosky

I’m restoring a 67 GTO, stock 3.55 rear end too low for highway use. Looking to rebuild rear end (add posi-carrier) and would appreciate a suggested ratio and corresponding tire/wheel sizing. 400 cu” engine getting tooled to about 425hsp. Want both acceleration and 70 mph comfort (not 4K rpm). Thank you, Bill in Oregon

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Personally, I’d look at an overdrive transmission conversion, or putting a “Gear Vendors” unit inline after the transmission.

You could put a 3.08 or something in the rear but I doubt you would he as happy.