A fundamental part of any muscle car is a nice, strong rearend fitted with a limited slip or Posi unit. What good is it to make gobs of horsepower if you can only do one wheel burnouts or if the diff grenades the first time you put the spurs to your new engine? Plus, the best way to transfer that power to the ground is through two tires, not one. Lately the trend has been to ditch the factory rears for a 9-inch, but not everyone wants Ford-style parts on their Chevy. So for all the purists out there, we are going to rebuild a 12-bolt with stronger than stock parts and add a new limited slip differential.
The rear end in question is out of a '66 Bel Air that now has a stroker small-block and a 4L60E overdrive transmission. Not only will we add strength and traction, we'll also change from a 3.08 gear to a 3.73 ratio, which is better suited for acceleration and an overdrive. With the 4L60E's 0.70 overdrive gear ratio, a 275/50/17 tire (27.83 height) and a 3.73 ring and pinion ratio, the engine will be spinning right about 2,000 rpm at 65 mph, which should be perfect for decent gas mileage. We picked up everything needed for the upgrade/rebuild from Moser Engineering and took it all to Steve Post at Diff Works (Corona, California) to have it installed and set up correctly. Once the rear end is finished we'll be able to lay down two fat black marks with confidence.