i have dynomax standard series headers, they have an o2 sensor fitting and the holes for the air box? i dont have one but i was told thats what they are for but i have mine plugged, you can use your stock y-pipe, but using a single muffler and a y pipe kind of defeats the purpose of having headers, i have that set up right now but i plan on buyin another dual outlet muffler to go with the other one i just havnt had the money yet, but these headers are 120 bucks from jegs and they are ceramic coated, i really like them and havnt had any problems with them and best of all they havnt leaked.