Don't s/c still need good exhorts velocity unlike turbos? If that is the case bigger is not better and I would think a straight through 2.5 would be a good size.

I'm guessing its all new exhaust for me this year.
Now I have to decide between 2.5 and 3 inch. I'm not to concerned about the noise. I just want good flow.

2.5-3.0 inch exhaust needed for 150-200kW.

yes. big fine if you dont. inpounded car if the cops in bad mood

Do u have to run a cat legally?

Using 3 inch system with S type muffler, hot dog and cat (CA). Cat is a bit restrictive, reduces top end power. 2.5 inch tip. Without tip the engine is a bit noisy.

I just realized something yesterday. Last year I had a new 2" exhaust installed. Glaspak muffler and no Cat. So basically a straight pipe. Stock KA24DE 240SX has 2" but with restrictive muffler and Cat.
With the supercharger, the 240SX websites say you need 3" pipe.
What are you Modified 1200 people using? (CA, SR, L etc.)
And what should I use?