if its stamped, it should matter...some mufflers and resonators are not "straight through"...they actually have little hoops that "grab" the exhaust flow INTO the muffler packing (aka louvered)..if your muffler is not facing the correct direction, then the exhaust flow is just being blocked by these opposite facing louvers....if your muffler is generic, it either has these louvers, or the aforementioned baffles....or even both. the direction makes a difference in both sound and performance...