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What kind of acceleration gains could I get by modding my rear diff? What if I put in a 3.73 or a 4.10? How much would this cost me?

I just got talked into test driving an '06 beautiful black/black M3 (with the competition package, too) at crevier BMW and I want it. :( Obviously, I can't afford a 62K car as a 21 year old student (although the salesperson swore I could :tsk: ) but I was wondering if I could get that "seat of the pants" feeling of shear acceleration out of my 540i with a new diff...?

Also, I don't really care about fuel economy or top end (I chicken out over 140ish anyhow) so, is a 3.73 or 4.10 LSD (or even open) right for me? Where could I get one? Thoughts people, thanks! :)
 

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I think I remember seeing an LSD for our car (don't remember what "size") for around $1500. After seeing what it can do to some of the E46 guys, it would make a huge difference especially in the lower end. The diff will give you quite a bit of torque multiplication, which the M62 is already plentiful in.

I say do it, be the first!
 

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Look in your Roundel and Bimmer magazine ads.

Metric Mechanic also has them I believe. They are a good source.
 

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I had a e46 330i with the performance package and I swapped the diff in for a 3.46 from a 3.07. It made a nice imporvement and I would have a went lower (numericaly higher) had I had the chance. I think a 3.73 or 4.10 would be an excellent improvement in acceleration for your car. Expect 1st gear to be over very quickly and you will have a hard time getting the rear tires to hook up withou LSD with either gear ratio. Also 60 mph wont be reached in 2nd gear making your 0-60 time longer since you will have to shift to 3rd but who cares. With either gear ratio I don't think you will have that rush of speed that you get from the S54 motor. The power to weight ratio will still be favored on the M3 and the motor is simply more powerful. I would recommend forced induction to take care of your needs.
 

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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 :)
 

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and the authority in BMW gearing [/QUOTE]

How's that?

There are 3 or 4 ratios to choose from. That's the end of it.

Where does expertise come in?
 

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Demetrios540i said:
could you use an m5 diff. ?
I recall reading they are a direct swap but expensive. Maybe someone here knows for sure.
 

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The M5 dif is not a direct swap. You need to replace the half shafts along with the dif. Dave Zeckhausen did this and posted about it on Road fly a couple of years ago. Its a lot of work.

I too am thinking about this and I've talked to Koala motorsports a couple of times. The owner -- Brett Anderson I think it is -- does difs for lots of BMW racing cars and writes for the tech column for the BMW CCA magazine Roundel. He's also very patient with stupid questions. I'm planning to buy from him when I get the coin scraped together.
 

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Demetrios540i said:
also...how would it effect an automatic trans?
No problem. Same as a manual box.

Car would go thru the gears normally but top speed in each gear would be reduced.
 

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fm_illuminatus said:
What kind of acceleration gains could I get by modding my rear diff? What if I put in a 3.73 or a 4.10? How much would this cost me?

I just got talked into test driving an '06 beautiful black/black M3 (with the competition package, too) at crevier BMW and I want it. :( Obviously, I can't afford a 62K car as a 21 year old student (although the salesperson swore I could :tsk: ) but I was wondering if I could get that "seat of the pants" feeling of shear acceleration out of my 540i with a new diff...?

Also, I don't really care about fuel economy or top end (I chicken out over 140ish anyhow) so, is a 3.73 or 4.10 LSD (or even open) right for me? Where could I get one? Thoughts people, thanks! :)
Check out www.Diffsonline.com , the website explains the different setups and gives you a chart of gearing VS speed ..... Dan's builds are considered some of the best in the racing world....
 

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Discussion Starter · #13 ·
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 :)
It Jim Blanton in my area? I did a gear calculation and I think I may just go with the 3.73, because the 4.10 cuts too far into my top end (brings the max below 140 I think, which mean really high revs in 5th.) I only have 5 gears, being an auto, so it's an issue.
 

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Demetrios540i said:
could you use an m5 diff. ?
doing the M5 diff swap is probably the cheapest if you can source out a complete set. if not, it does get a bit expensive but not as bad as other solutions which could easily be $1000 more.
 

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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:
That would take 1.5 seconds off your 0-60 time.
 

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franka said:
No problem. Same as a manual box.

Car would go thru the gears normally but top speed in each gear would be reduced.
No the automatic is a different length than a manual transmission therefor you will need a custom driveshaft made to fit a M5 diff as there was never an automatic offered for the M5 hence there is no OEM part.
 

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MJTSUB said:
No the automatic is a different length than a manual transmission therefor you will need a custom driveshaft made to fit a M5 diff as there was never an automatic offered for the M5 hence there is no OEM part.
IF ... If the original question that Demetrioss asked was about fitting an M5 diff in his automatic car the answer should be no problem because he is just swaping out diffs. He already has the auto box and the correct length drive shaft.
 
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