I'm driving 2 hours to buy a Z28 disc brake rear-end with 3.45 gears and have it installed...I wanted to know would that gear ratio mean terriable hwy mileage? And would my speed display be way off and more importantly would it burn up a high mileage transmission

 

the difference it makes will depend a lot on what you have now. if you have a 3.23/ 3.27 you will not notice much difference. yes your speedo will be off until you have the speedo gears in the tranny changed to the right ones. doubt the tranny will care one way or the other. if it burns up it is because the damage was already there. as far as mileage, i get about the same with my 3.42 as i did with my previous 3.27.

 

but I have 2.73 open end now. So I would say it is a big difference..Any body else have input it would be appreciated.

 

What 87zjeff said. The seat-of-the-pants dyno, with the change, will make you smile. The difference in gas mileage may not. Everything's a trade-off. Personally, I'd go for it.

JamesC

 

After doing some research I found out the axle is the warner borg that came on M5 and is ratio of 3.45. Is it LSD or POSI..And most importantly is it worth it?

 

If the posi isn't burned up then yes it was originally posi.

As far as the 9 bolt rears go 3.45 is the most sought after.

An important question is what year car did the rear end come from hopefully it will be 89+ and you'll get the PBR brakes.

Also as far as I know since you have 92 w/ an electronic VSS you will not need to change out any speedo gears.

 

A transmition doesn't care what kind of rear you have. The rear is like a 1 speed tranny. imagine you had two T5s in a row. The first doesn't care what they second is doing. They are changing the torque output, not input. The power is constant and the torque just gets delivered slower though a tranny.

In a nut shell, your tranny will never blow from swapping those gears in. It might blow from you romping on the car more after you find out that they are more fun.