One of the big technical differences is that the 80/90 Quattros use a Torsen dif. I believe that the intake system changed but I am not sure how. Anybody want to share horsepower and torque #'s for the 4000. The 90 is 130hp and 140lb-ft of torque or 136hp and 137lb-ft of torque depending on where you look. Brendan Rudack 88' 90Q Boulder,CO