General LSX Automobile Discussion - slowin down

installed a 9 inch rear in my car with 3.89 richmond gears and a spool with 31 spline axles. I had a stocker with 3.73 gears. My car is a 02 ws6 m6. Seems like the car slowed considerably with the new rear, sounds crazy, i know, but does the 9 have that much more rotating weight and mass to cause this?

No, not usually. Is this "feeling" seat of the pants, or do you have some track times to back this up. Report back with track times and let us know. Eric L

No just installed, havent had it at track yet, but there is definite noticeable" seat of the pants" difference

I believe it no doubt. If your anything like me then you know your car just like its attached to your body. Call me crazy but I could tell the difference after taking the back seats out of my car and its only 30lbs.

OP may be on to something. The 9" has more parasitic drag than a 12 bolt. I am not sure how noticeable it is though. Chevy High Power or GM High Tech did a test that included these two rears and maybe a couple of others too. My memory is that the 9" had the most loss through it by a large margin. Obviously it is very strong so it is a good choice, can't remember how the 12 bolt compares to it strength-wise...

Yes, because of the offset pinion, the 9" has the most parasitic loss. Acording to the article that Jeff Smith did in chevy hi performance, the 9 inch had a 10 hp disadvantage compared to the 12 bolt. Eric L