I called Arospeed and one person I spoke to said the one for the civic/integra or just civic (same thing) was 2.5". I just looked at my notes: it's Alfred at ext 306 who told me 2.5".
I plan on calling again and speaking to someone else to confirm it (with more certainty). (I call a lot of performance companies and sometimes I get different answers.)
I have it on my car and love it. I don't believe it affects performance very much at wide open. If it did I can't see the thin plate robbing any significant amount of power.
Yes it's great to open her up when you want the power but otherwise stay quiet when cruising around. I like cruising with it 3/4 closed, and it's very quiet at this setting on my custom exhaust with no resonator and only (2) 45 degree bends. I've cruised by cops with it 3/4 closed and I don't get any special attention. Fully closed on my setup is almost as quiet as stock. But fully closed feels like the gasses are getting backed up and having trouble getting out... like a constipated Celica ew
. Now who says there is no such thing as _________ lol . I can start an argument with at least one member, but I don't have time now to try to explain to someone who might not ever understand it. it's good fun though. anyways...one argument at a time and I'm currently occupied