I have a 2000 si b16a2 and I currently have a tanabe racing medalion exhuast on my car which is 60mm (about 2.36"). The guy at the muffler shop by my house said he could make me a downpipe for about $100 but was very persistent with the need for a 3" DP and 3" piping all the way back. I will be running a 14b at 8psi and Im guessing only about 210-220whp and 3" all the way back sounds like a bit much to me. My question is, whats a good size DP/exhuast diameter for my setup? I would really like to keep the exhaust i have on there now and maybe get a 3" DP that could collect at the cat or maybe delete the cat with the DP or something. Is it alot louder without the cat? Is it illegal without the cat? Someone please enlighten me on how this whole thing works. Thanx!

 

yes in almost all states it is illegal to not have a cat. your exhaust will only flow as much as the smallest part of your exhaust diameter. 3in downpipe and all the way back would be perfect because you will more than likely upgrade and wont have to spend the money again down the road.

 

3" all the way back, you will thank yourself later.

 

doesn't it really depend on the exhaust housing on the turbo? my housing only has an outlet of 2.25" so i'm only running a 2.25" downpipe and 2.5" exhaust that i had before. would it still be worth it to go bigger even tho the turbo outlet isn't that big?

 

Yes, but if you have 2.5" now just keep it until you decide to go 300+

 

I wont be making more than 230whp on this motor. In a few years I plan on rebuilding the motor for alot more boost and uprgading the turbo and alot of other stuff so I wont mind shelling out the cash then but for now Im assuming I'll be alright.

 

Seriously, if you're going to shoot for high power at any point in time, just throw in the money for a 3" now! You will be having to sell your entire exhaust all over again and make a whole new one for it, when you can just have overkill for a while and then run it with your new setup.

3" all the way back, hell, guys in Cali are running 5" downpipes and 4" all the way back!!!