OK guys, I've been thinking about going to a local muffler shop with a good rep and getting some custom work done. I'm considering a piece that will extend from the headers all the way to the stock muffler (yes I am keeping that stock). I am thinking about running 2.25" dual piping to replace the cats and a new y-pipe running into a single 3" pipe with an aftermarket resonator to extend back to the factory muffler. I'm thinking the larger piping will help increase flow while keeping the stock muffler will maintain some backpressure. Thoughts?

 

i think this was tried and cause problems on the guys ts ecu upgrade. ran way to lean and made no gains hp wise. if you do a search i think its somewere here with pics

 

That sounds like the NISMO exaust.

The Nismo exaust has 2.5" piping coming off the cats and then 3.25" going to the resonator and to the muffler.

 

I have never seen the Nismo in preson but 3.25" seems way to big. Is that right?

 

Its correct.

The exaust is designed properly.

off the cat's is 2.5" then the Y pipe joins at 3.25" and the whole SINGLE pipe section is 3.25" through the resonator and into the muffler.. then each pipe out of the mufler is 2.5" to the 4.25" tips.