Based on what I have read and gathered the GS400 has 2.25" exhaust piping throughout. As all of you may know (from a recent thread of mine) I have a crack in my Y-pipe and will most likely replace it with an X-pipe and do the S&S headers in one shot. I also decided that I probably will not go the FI route...ever. If I want more power I will probably get a re-build from Lextreme or something down the road and stay N/A. With that in mind (never going FI) should I stay with the 2.25" piping or should I go to 2.5" or even 2.75" piping throughout? I have a basic concept that the larger the exhaust pipe the better flow and exhaust gets expelled quicker but I understand from what I read if you go too large then it may actually slow your car (and hurt performance) if you are N/A. For FI cars especially turbo I realize that a larger exhaust size is always better in many cases but what about N/A? I would like to do a full custom exhaust with an X-pipe, the S&S headers and still retain my Borla rear-section exhaust. I just need some advice and for instance with regard to the size I should choose for my particular application. Let me know if you have experience with this. I know some well-known members like Hameed did a full custom exhaust. Maybe someone can chime in and help me out based on their experiences. Thanks!

 

Actually, GS 400 exhaust is just under 2". The Y pipe section has a smaller diameter than that, but I am not sure of the size.

 

the pipes from the cats to the center are 1.97" (50mm)
the center single pipe is 2.36" (60mm)


These are GOOD sizes even with the headers and make good low and mid rpm power and torque. Run the headers with the stock pipes for great results.

 

That's all I needed...and based on your previous posts you seem very knowledgable. One final question though...Let's say I wanted to buy a Tanabe or Apexi cat-back exhaust, what size piping do these systems come with? Same as factory? What is the benefit of these cat-back exhausts over my Borla Rear section?

GS FONZy - Thanks for your input as well man.