Well, factory tuned(stock ECU) froced induction cars almost always come set up to run pig **** rich(like insureance for the manuf.)!! I would put money on the fact that your stock fuel system has some room left for a few P.S.I. increase YES it will lean you out some more but it is possible to still stay safe. I would either get up with the guys at APR on how many PSI increase is safe on a stock TT and what a safe AFR(air fuel ratio). OR, if you are gunna really start to let that little TT be all it can be once ya figure out what your ideal AFR is (I can only speak for my turbo neon srt-4, witch has bout'a 12.2 AFR now witch is still safe but for example my car stock has a rich as hell AFR of like 9.0 or 10.0) you should really invest in a Wideband O2 setup they are like$250-400 and worth it cause you can monitor your AFR all the time and set up your boost controller to a safe PSI without worrying bout blowing your **** up! Wideband is the way to go really cause climet changes in temp. can effect AFR also, say its like 80* out and your AFR is a safe hypeathetacal 12.0 drive the same car on a 30* degree day and guess what? Yup, youll be running leaner by 1to 2 points that can be BAD so be careful,do some more research, and again be careful.