what's the best exhause diameter?
 

hi guys, I'm just wondering what's the exhaust size that you guys are running at? I'm getting new muffler and I'm debating if I should get 2.5" for torque or 3" for high end hp... I'm more of a city driver, so I'm slightly leaning towards more torque... what do your guys suggest?

I'm not sure if this is a legit question but most everyone here goes with 3" from the turbos back.

Re: what's the best exhause diameter?
 

Depends on what ECU and boost control you have on the car. If you are on the stock ECU, full 3" all the way out could give you uncontrollable boost.

If you are keeping the stock cat, then it really won't matter.

the diameter of the exhaust is to create little or more back pressure. As I read a book on turbo and turbo engines, it was said that the larger the exhaust the better for turbo cars but not the same for NA cars. As a more open or larger exhaust pipes will give you more boost.
as I am running a full exhaust and at WOT I get boost above 15psi of boost for a sec or 2 then slowly dropping back to 13~14psi

the reason I ask this question is because I bought my car used and the last owner did the weirdest system I've evern seen.. if you look at the exhaust, it loos like he did some sort of custom work on the d/p. looks like it's 3" dia, but when it hits the midpipe, it's back to 2.5" but there's no cat there.... then the rear section is 3" again... the car has no torque, and sometimes hesitates at low RPM... and like Mahjik said, the boost is sometimes really uncontrollable.. but I do get 10 psi. and I'm still using factory ECU. but I'm installing the Profec E-01 and E-manage within the week.