Is this link any help?
http://www.bokchoys.com/differential/GearRatios.htm



I think the e9x m3s have the same lsd unit that's in the e46 m3. It's purely mechanical.

'What is the M Differential Lock and how does it work?
The M Differential Lock, fitted as standard equipment to every E46 M3, is an advanced version of the traditional limited slip differnetial. Though still entirely mechanical in operation, the M Differential Lock is activated when there is a difference in rotational speed between the two rear wheels. This difference pressurizes a viscous silicon fluid, which then operates a multi-disc clutch that directs more power to the wheel with the greatest traction.'