I'm going to build a new y-pipe over Thanksgiving to replace the crappy Hedman piece I've got on there. Right now I'm thinking 2.5" pipes out of the headers y'ing into a 3" pipe with a 3" E-cutout, reducing back to 2.5" to keep the cat and cat-back I've got for now. Would it be overkill to use 3" for the entire y-pipe? Use 3" from the collectors instead of the 2.5"? Any reason not to do it? I will be spraying atleast a 100 shot of nitrous, if not a 150 or 200, at some point in the near future, and I'm already pushing over 400 at the crank.

 

2.5" from the collectors is going to be fine. There are some stock-appearing-drag types going through dual 2.5" all the way to the rear bumper running 11's in heavier cars than ours.

 

works for me. cheaper too