I'll only add something quick in this, for about 6 months i tryed using standard 91 ron fuel in my s2 96 r33, and now im paing the price, my car is now choppying when i try to boost higher, lack of fuel when its needed, been using 98ron now and it ran ok for a while but not perfect, no the issue is happening again, maby dirty injectors from the 91ron fuel?, finding out soon. but it is a fuel issue , ran very very bad on 91ron, very chopping when giving it power