Hmmm I would say if the protruding holes ("clamshells") are facing the back of the car, there shouldn't be any additional restriction. However if you have the 'clamshell' holes facing towards the car, yes there would be some, but it should be quieter? I had this exact muffler installed into my car last week. Works quite well. No longer get headaches lol. I had them facing forward as I don't minding loosing 1 or 2 rwkw for a few more dB!