Mh, yes, I hope it will work .

I though Dinan has a final drive ratio for the 545

Dinan does and it costs $2K just for the part. The final drive ratio is 3.45 and I think it's coming from a 645 Step.

ok, im going to plead utter ingnorance, what does in short a differential do and why is it beneficial to swap it out (use my car for example-530i). thanks

I need the differential of the 645ci manual/SMG : 3.23 .
1300e+taxes, here in my country .
I have to decide how to solve this situation ..

I am going to def. do the Dinan 3.45 Upgrade. If you know about torque multiplication, these gears would be the equivelent of an 18% increase in TORQUE!!!! So for the post that questioned what the gear change would do it would FEEL like the 550i had 425 lb ft of torque. Dinan has had the 3.45 set up for quite a while and it was very popular in the E39 M5's as best bang/buck upgrade.

Chris

Jetblack, I don't have the Steptronic but the SMG .. Thus I don't want gears so short like the 645ci steptronic (3.46) : I want 3.23 and gears with the following speeds (kmh) :

56-104-157-209-251-289

And I need 3.23 .

The diff costs 1100+taxes (530i manual/smg) or 1300+taxes (645ci manual/smg) .
[euros]

Dinan has a 3.23 diff with LSD ?
No, otherwise ...

Basically, when you change the differentail ratio, (higher numerically the lower the gear) from say, 3.15 to 3.63, this is actually lowering the gears of the car, thus giving you a little more off the line but losing some top-end speed. The problem with having "more off the line" the ring and pinion are smaller, therefore, weaker and subject to breaking unless the differential is larger or a different type. For the 530i, changing the ring and pinion would be only thing you really need to do, i doubt that you need to change the whole differential as I would expect that the smaller gears could handle the increased torque. However, if the car is equiped with a traction devince, in some cases the ring and pinion can become too small and you'll need to install a new traction device that fits.

4WD vehicles often change the ring and pinions (differentials), transfer case, and sometimes the transmission, to obtain a lower crawl ration which adds torque and slows the vehicle enabling rockcrawling at a much more effecient pace. This is also necessary when vehicles add larger tires as it helps keep the vehicle in a good (stock) rpm range.

Reviving the thread. :)

I was at CarLab, a tuning shop, in San Jose a few days ago. Darwin floated the possibility of changing the final drive ratio from 2.93 to 4.1. He mentioned that all that needs to be replaced is the ring and pinion. That there would be no need to swap out the existing diff for another one. Is this feasible and if so, where do I pick up the ring and pinion from? Maybe bimmerworld.com?

I'm sure AlexFW will be happy to hear someone else is wanting to change the final drive ratio. I'm back to modding again. :D

Just got word back that RDSport has the ring and pinion. I was also asked if I want to get the 4.1 with LSD! I told Darwin to get quotes for 4.1 and 4.1 with LSD. Stay tuned. If all the numbers work this is going to happen quickly.