I fired up my 2.5 NA Mazda3 with the muffler removed and it wasn't completely obnoxious, but it wasn't pleasant. For a comparison, the CorkSport Axle-back and Catback exhausts for MZ3, CX3 and CX50 all have a single muffler on one outlet and a straight pipe on the other. Semi-muffler delete and they are still not that loud. Turbo models should be quieter still as the turbo muffles much of the exhaust as well. Back in the 00's, the SRT-4 Neon had no mufflers, just a mid-pipe resonator and was still road legal, from the factory.