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AirFrcd said:
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 :D ).
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 :)
Are you implying that your car accelerates 18.5% faster due to a diff change?
 

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AirFrcd said:
How do you come up with this number, 18.5% !?!?!?
 

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franka said:
The ratio of the 2 gear ratios.

4.10 / 3.45 = 1.1884 = 18.84%

I'm just showing where he got it from. I'm not supporting it.
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
 

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franka said:
s62 said:
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.[/url]
A higher numerical diff ratio is going to improve acceleration.

An extreme example to make the point obvious would be to imagine starting a drag race in 2nd or 3rd gear. Dropping to 1st gear would yield the same type of improvement as going to a numerically higher diff ratio. It would improve acceleration.

Most drag racers run a 4.10 or 4.56 diff because it works.
I assume you are not talking about BMW 540/M5 and keep in mind that you cannot compare diff ratios between different cars because their gearbox ratios may be way different.

My point is this. I have not been able to get ANY hard data on performance improvement in 0-60 og 1/4 mile times with the change from the stock 3.15 diff to 3.45 or 3.64 in the M5. I have repeatedly asked people to show me that this mod does result in better times - nobody has been able to. And in the thread I pointed to earlier it is suggested that the cars with stock gearing 3.15 do better 1/4 mile times than the 3.45 ones.
 

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AirFrcd said:
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:
Sorry, I did not mean to imply you said it increased HP - I was just stating that diff ratio changes have no effect on power output, just torque to the wheels.

I think it would be very interesting to have Mr. Blanton back up his claims with some hard empirical data. I think this just goes to teach people not to trust salesmen :)

I think it is just the SC that is giving you the quicker acceleration ;)
 
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