Originally Posted by GeorgeSmooth
I remember you mentioning that with the shorter ratio you could not get the traction down. I had the same problems with the M3 diff but what I did is a tuned in a far less aggressive boost map, stepping it up very gradually and it seems to have done the trick in terms of traction.
I'm impressed you remember my comment so long ago...
Well, the prespective of using an /M diff in a non-M car is really interesting but using a shorter final drive ratio is mistaken (in my opinion ,of course).
There is no need to use a shorter final drive when you have a car that performs the +50% of its maximum torque from 1200revs ,like 335i.
A shorter diff would be ideal for the naturaly aspirated //M cars that needs to reach their beneficial rev range fast (which is pretty high at 5500revs+).
Again, I find impressive your whole experiment from a technical view, but in your place i would roll back to your quaife one