[AirFrcd]

Depending on what your final drive is geared at now, let me tell you, upgrading my diff. from a 3.45 to a 4.10 LSD was by FAR the best mod that I ever performed to my 5'er :thumbup:
A net increase in accel of 18.5% is very noticeable, and a match made in heaven w. the forced induction (as the s/c kicks in only past 3K RPM's, and the shorter gears kick in as soon as you touch the skinny right pedal ).
Cost was approx. $3,600 from Jim Blanton at Performance Gearing - btw, he is an awesome guy to deal with, and the authority in BMW gearing. I highly recommend his work and services

 

[AirFrcd]

Are you implying that your car accelerates 18.5% faster due to a diff change?

Yes.

 

[AirFrcd]

Ok, this is where the crazy number is coming from

Diff ratio changes do not increase horsepower.

Diff ratio changes do however change torque, you get higher torque multiplication BUT (and this is a bit BUT) for _shorter_ amounts of time because the shorter gears.

The result is an increase in the "butt dyno" because of the strong but short torque bursts but you are not getting a big increase in acceleration.

This has been discussed alot on m5board, see this thread for one: http://www.m5board.com/vbulletin/showthread.php?t=67150

I never stated that a change in diff ratio increases HP :dunno:
However, and I quote Jim Blanton from Performance Gearing "... and changing your diff from a 3.45 to a LSD 4.10 in a 530 will result in a net gain in accel. of approx. 18.5%."
I have not gone to the track / strip (yet) to test my times - however from a daily driver perspective (yes, I do drive my car hard), I can tell you that the increase in accel. is SIGNIFICANTLY noticeable and an absolute blast to drive (especially when combined w. the s/c) :thumbup: