From my experience when my car was an NA with the RSR GTII catback exhaust you know when I was coming around the corner, very nice deep sound. When I got the car back after the turbo install the same exhaust now sound a bit mellower and not as loud as before except when I'm WOT. I was told the turbo makes less exhaust noise and I actually noticed the difference and I have no cats on the car. hope this helps.well does the hi power sound differently on an NA than a TT because I heard it on a tt and you could barely hear it. I just don't want an overwhelming sound, but I would not mind a nice tone.