It depends on cams and boost how much you can rev it.I had reached the limit of my standard springs at 1,5 bar and over 7000rpm(around 360bhp). Then we put in an inner spring from Audi which fits perfect inside the standard one, and now i run 2,2 bar boost and rev to 7800rpm max. cheap and functional! This on BD 14 cams, around 450 bhp.