Subaru placed that exhaust on there for a reason you already know. Its not approximately how briskly the vehicle can go, its approximately how briskly the motive force can take care of. maximum folk does not final fifty yards in a rear force Italian marque. changing the exhaust may be like asserting Subaru are incorrect! . . . no one should be that guy. . . . don't be that guy!
Well as it's naturally aspirated a full exhaust system isn't going to do anything in terms of power gains. However you could probably get a part exhaust system or a different muffler if all you want is the Boxer rumble. It'll be a lot cheaper and it'll make your Scooby sound pretty sweet.