Didn't know the 12 bolt is roughly 3.5% more efficient and about 30lbs lighter than a 9" (though 9" can drop 15lbs on aluminum 3rd member). But you trade pinion strength for this higher efficiency so at my GTO power level I'll take the 12 bolt but for my GN that's already 850tq and going higher in the future, I'll go 9".
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69 GTO Convertible, 4000lbs
462ci, 606tq/569hp - 93 oct @ 34 deg (207psi)
11.7:1, KRE H Ports, Lunati HR 282/290 w Johnson Lifters & 1.65 Scorp, E30, EFI, Holley HP + Dual Sync, 12-1 Crank Trig, 120lb Inj & 1000cfm TB, Torker II EFI Int & Rails, PTC 10", Rock Valley SS Tank, Dual 450s, Aerom EFI Reg, Aero Front & Wilwood Rear Disc Brakes, Dougs 1 7/8" & Borla Pro XS 3", Alum Rad & Dual Fans, 12:1 Box, UMI Arms & Viking Berz Fr + Rear CO Shocks, Hella UP5.0 Vac Pump, 12 Bolt, 3.73, 33 Spline
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