Originally Posted by Nikolas
The XI system is not that basic. It is one of the only AWD systems that can vary power 100% f/r. Most others have a limit.
Sorry to bring this thread up (but i got some info), apparently cheaper versions of Quattro in TT and A3 work the same as BMW X-drive (with computerized clutch packs) and also can transfer power up to 100%. So it turns out that 100% transfers are not ideal for performance, thats why B7 S4 and RS4 use 40/60 (old technology). Also "clutch packs" AWD systems are used because its very easy to integrate into FWD or RWD car to make it AWD. With torsen system (or others) you actually have to redesign and redo the whole system from the start.
Now the newer Quattro system with sport differential used in B8 models can transfer torque from front to back, and from left to right as well. And I haven't even seen any comparisons with this setup yet, only read that a car handles really like on rails.....
And thats not it, the very new torque vectoring Quattro is used in 2010 B8 RS5 which is supposed to be even better then 3 above.