Originally Posted by NtacomaR
ok so i decided to go with the Y-Pipe. Because the o2 sensors only monitor the front Cats near the headers. So the Cats connected to the Y-pipe basically arent doing much haha...so with a CAI, URD Y-Pipe, and TRD exhuast should i yield some good performance???
Interestingly, I was underneath and '11 yesterday, messing with the driveshaft. I decided to take a good look at the catback. They have improved greatly over the earlier models. Not sure exactly when, but the catback used to be 2.25" diameter. On that guy's '11, it was 2.5" all mandrel bent, and very nice. If the is a restriction in it, it is strictly due to the muffler.
So to upgrade your catback to a TRD one, unless you just really want to, I would only change the muffler, to alter the sound to your liking.
The factory y-pipe however, had not changed, and was still the same restrictive design.