I'm not too sure what the difference in weight is between the stock rears and a 12 bolt. I guess around 30-50 lbs. What changes in performance have you guys seen after installing the new rear?

 

I swapped out my whole rear suspension at the same time; so I had a combo effect; but my car handles and launches totally different now. No wheelhop, no worries about the 3K-4K clutch drops, the traction off the line is amazing now; although I'm thinking most of this was due to the suspension swap.

I think the only way you'll see a performance gain is through a gear change when you changed out the axle.

 

I weighed the stock 10-bolt when I took it out, and the Strange 12-bolt was only about 10-15# heavier. I doubt you will see much in the way of additional drivetrain loss, because the geometric relationship of the pinion centerline to the axle centerline is similar in both rears. Its dropping the centerline of the pinion that causes the 3% additional loss in the 9-inch.

Comparing my engine dyno numbers to chassis dyno numbers after the engine was installed, at the 500flywheelHP level, I only lost 12.6% in the driveline. That for a steel FW Street Twin/T56/3" chrome moly DS/3.73 12-bolt running on 17x9.5" wheels with 275/40-17 street tires inflated to 32psi.

 

I the local car club hear in fl we had one guy with a stock bolt on ls1 with 3:73's to to a 9 inch 4:30's with carbon fiber driveshaft no other mod changes and the when car was dynoed He lost 8rwhp.

 

The 9-inch has 3% higher losses than the 12-bolt.

 

when you beef of your drivetrain, you sacrafice power and add a pound or two. Not enough to make a difference or be all worried about though.