3.45 Differentials With Custom Locking - Page 2 - BMW M5 Forum and M6 Forums

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Old 17th October 2003, 04:02   #11
ELEVENS
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Hey Ben,

Welcome to the board...THANK YOU for becoming a sponsor.

-Bill
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Old 18th October 2003, 01:20   #12
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Bill,

Thank you. We recommend a 40% lockup for any street car. In icy conditions you will actually be able to go faster with more lockup.

DDB540,

To upgrade to a 3.45, you would need to convert to the M5 differential core, which would require changing parts. However, if you would like to do a 3.15, 3.38 or 3.64 it would not be necessary. Pricing is a little higher, as the stock differential does not have limited slip. Please contact me for details.

Thanks,

Ben
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Old 18th October 2003, 02:45   #13
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Hey Ben,

Nice avitar.

Does the amount of lock effect axle hop at all.?

If you have a higher % of lock will it eliminate axle hopping?

I haven't tried a burnout yet with the new clutch, but the old one would often induce axle hop.

Regards MIJ from MIB
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Old 18th October 2003, 08:31   #14
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MIB,

Thanks! Brad handles all of our graphic designs--he's great at it.

In regards to your question, a higher lockup would increase traction and thus reduce axle hop.

Thanks,

Ben
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Old 19th October 2003, 03:23   #15
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Ben:

Since I'm one of those that live in the Southern California area ... and I could have Evosport suppy and install the Differential ...

WHAT would be the INSTALLED price of the 3.45 Diff?
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Old 19th October 2003, 13:55   #16
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BEN....I've spoken to Wayne about what he thought of a 3:45 diff he drove some months back....his reply was it transforms the way the car feels
I see you've got shorter diff's then just the 3:45, wouldn't the shorter options make the car too snappy at lower speeds and therefor you would be left trying to keep the car all hooked up in anything but perfect conditions from 1st to 3rd
My particular motor makes less power then a stock unit in the 1,500-4,000rpm zone, so l would think going with a shorter gear is going to help me get hold of what power there is on tap, and give it some old stock punch back in the low-mid RPM's. Now above 4,000rpm it's going to be one very quick trip to the 7,600rpm limit
Question....Does 1st gear with the 3:45 or any of the shorter options make 1st too short for quick take offs....reason...problem getting traction if you're pushing pretty hard???
In a stock M5 you can short shift into second at say 3,500rpm and pull away with full throttle from then on. It seems as though you're never in 1st for very long as it is now with a 3:15, you're changing into 2nd at the 3,000-5,000rpm zone (15-30mph)
Maybe l've answered my own question about the shortness of 1st gear.....I just looked at the max speeds of the 3:45 option and what max speed for each gear you would loose @ 7,000rpm
1st - 3 mph
2nd- 6 mph
3rd - 8 mph
4th - 12 mph
5th - 15 mph
6th - 17 mph
So looking at 1st gear there really isn't that big of a difference between the 3:15 & 3:45 in respect to the top speeds for 1st and maybe 2nd gear @ 7,000rpm.
Any of you 3:45 guys out there got some buttometer readings you can tell me about.
Thanks BEN
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Old 19th October 2003, 14:18   #17
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What about extending the gear ratios in 1st and 2nd gears up 9% as thats what the 3:45 does, you would then be giving the car the same loads on the clutch in those gears (1st&2nd) as if it were stock.......I say this because 1st & 2nd gears are the gears that will fry a clutch with ease if miss treated a few times, so with a 3:45+ diff you will be stresing the clutch even more with some aggressive driving at lower speeds
This would mean that a 3:45 car in 2nd with the extend gear raio would have the same max speed as a stock 3:15 rear end. The max speed then for the adjusted 2nd gear ratio with the 3:45 would 67mph (same as stock 3:15)...now when you would change into 3rd (thats still running the same OEM ratio) the tacko will only fall back to 5,000rpm on the up change...right in the sweet spot of the M5's power band The normal gear box from 2nd 3rd it would fall back to around 4,600rpm on that particular change up.
I wonder about this mod maybe too costly to have to get into the gear box and change the 1st and 2nd ratios
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Old 20th October 2003, 00:27   #18
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Hey Apples,

I'm not going to tell you to change your clutch. But from reading the above post, it sounds like that would solve you problem.

When you get back to OZ., come and take Yoda for a Spin, and deceide for yourself. It would be good for another board member to give there independant appraisal of my clutch.

I had my first race yesterday with the new clutch. A HSV was in the right lane and I was in the left lane. My lane terminated on the other side of the lights, so it was a race to see who gets in front first.

I took off and was just pushed back hard in my seat with no wheel spin. I had plenty of revs that would have fried the stock clutch. I hit second and it gave a tiny Beep of the wheels and then I hit 3rd and again the same little beep and again in fourth.

The HSV was left in the dust, right from the start.

Now heres the kicker. DSC was ON. I got a slight churp in each gear with DSC ON. Sport was OFF also.

I was at the drag strip once with the stock clutch and left DSC ON. When I hit 2nd it almost throughs me threw the windshield. It was like you go from 100% power to nothing, then a couple of pauses and a settle then your away again. Too much interference.

Now I want to test this some more, but it seems that with the new setup, it does not continue to be invasive.

The best way to describe it is like comparing a worn shock absorber to a stiff sports one. When you press on the stiff sports one it goes down and then returns to where it was. The worn stock one goes dowe then rises above where it was and then goes down again less and then settles to where it was.

DSC with the stock clutch was like the worn schocky. Whereas with the new setup it is like the Sports shocky, it intervenes momentarily then realises all is good and leaves it alone.

Its hard to explain, but its like stock DSC is a wave on a spring that pulses backwards and forwards. But now it just travels straight through and gone.

Its a great improvement. Its raining today. I wanted to do some full blooded race launch burnouts. The clutch is run in enough now. 1,500Km Its smoother now as well.

Last edited by MIB; 20th October 2003 at 01:51.
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Old 20th October 2003, 22:44   #19
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Quote:
Originally posted by ben @ evosport
...Most differential upgrades are a replacement ring and pinion upgrade offered from BMW for motorsports applications. These are not built to custom specs and usually retain the factory limited-slip which is rumored to be around 15-20%. I am not sure exactly what the ratio on the Dinan is. ... For our street differentials, we recommend a 40% lock-up. What this means is that the wheel which is slipping will still be putting out 40% of the power of the other wheel. A non limited-slip differential would provide no power to the wheel slipping. A 40% lock-up is perfect for the street, as it allows one to power out of the turns quicker.

Thanks,

Ben
I have very limited knowledge of LSD lock-up percentages and their effect on the car's cornering behavior. However, it would seem that changing the lock-up % would change the car's understeer/oversteer characteristics -- I'm just not smart enough to figure out how.

Assuming the stock car is 20-25% (I've heard 25%), would a 40% lock-up increase or decrease understeer on dry pavement? What about on wet/slick surfaces?

thanks,

Mike
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Old 20th October 2003, 23:45   #20
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Hey LSU,

I may stand corrected, but the diff won't effect understeer at all. What it may do is Increase Oversteer as it will get more power to the ground.
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