I believe some people waited but did not have to wait. the only changes made have been slight and mostly cosmetic but everything on the underside will be the same. maybe magnaflows system wouldnt allow them to change the date range on the part so they had to add a new one??Magnaflow has different part numbers for the cat back for 2010 up, and 2009 and before. It's puzzling. From reading on this forum, some people had to wait a while till Magnaflow came with the #15583 for 2010 and up.
Thanks, probably 15583 is less noisy than previous due to larger size ? Who knows. Anyway, I was puzzled like you as to why 2 in1 for Fronty and Y design for the X, and called them. And the answer was that the "Engineer" designed the best system for each after research; So even using same engines, the "Engineer" decided a Y config for the X to be better!!!!!The only difference between the 15583 ('10+) and the previous 16654 ('05-'09) appears to be the muffler length.
The thing that I don't understand is that they went with a 2-to-1 muffler design on the '10+ Frontiers (#15580), but still used the crappy Y-pipe design on the '10+ Xterra. (Previous years Frontiers also used the crappy Y-pipe design.)
- 15583 comes with a 5 X 8 X 24 in muffler
- 16654 comes with a 5 X 8 X 18 in muffler