You don't need forced induction to be fast in this car at the track. Some good coilovers, 255/40/17 all around (RS3's), a few bolt ons and you should already be running with the 135i if not a lot faster if your driving is up to the task. I went from an E82 135i to an E92 M3 and now an S2K and this car is a ton of fun with so much potential to be fast NA. I'm only about 2 seconds off of my best M3 times on street tires in the S2K at the various tracks I visit.