I just got my mustang (been lusting for one for a while) and the dealership that had the one i wanted also had a 3:31 slip axle ratio optional on it and I was wondering what exactly that does? What is it better for and what is it worse for?

 

Its basically how agressive the transmission is geared to ur motor. So to put it simply and to the point 3.31 is the standard ratio on the manual, you can get 3.55's or 3.73's. The higher the number the more you will always be in the power band. With 3.73's you will be able to launch harder, and not have to worry about downshifting as much as you will be in the power band (higher rpm). However the 3.31 will have better driveability and better mpg and higher overall top speed. I have the 3.73's, and wouldnt have it any other way, i bought the 5.0 to get some grunt and the 3.73's bring that out even more. Hope that helps/made sense!

 

Explained easier....with a 3:31 rear axle, the drive shaft has to rotate 3.31 times to get the rear wheel to rotate one full turn. An axle that has a ratio of 4:11 means the driveshaft rotates 4.11 times to turn the rear wheel one full turn. The 4:11 axle is good for straight line performance, but would be bad for fuel mileage, as the powertrain is moving at a higher RPM to get the rear wheels turning. Again, this is good for performance, but bad for fuel economy.

The 3:31 is a good all around ratio. Decent performance and good fuel economy.