B4R says the Borla headers fit all 2.2s because Borla makes/made a 2.2 single port header & a dual port header for 1.8's, old 2.2 Legacys, & POS 2.5 head-gasket pop'ers so they have both designs covered.
Some of the older 2.2s had dual port heads. My 95 Legacy has them, and I think 95 was the last year for the dual port 2.2 heads. Not sure why they changed the design, as in my limited theory mind, it would seem more efficient to keep the heads dual port--what made them say "Hey, let's change the heads to single port"? Of course, my 99 EJ22 is rated with more hp than my 95 EJ22. Other than changing the sound of your exhaust tone, I really wonder if headers on a 2.2 with no internal mods would even do anything for hp/torque...
the singleports were a weird thing. im not aware of any definitive information that says exactly what years they are on, but AFAIK its only on 2.2L (never a 1.8 or a 2.5 that i'm aware of) in the 90s. i know they are at least on some of the 90-94 legacys and a 96 impreza 2.2L. i think my 95 impreza 2.2L had singleport as well, but i dont specifically remember. cant really speak for anything else because those are the only ones ive seen. all other EJ engines (not 2.2) have dual port
single ports probably increase flow or torque. if you look at the Hp ratings of the older 2.2L and the new ones, there is like a 5 hp increase. I doubt they arbitrailychanged the port size. someone who knows for sure can clear that up.
I was in the ECS show room yesterday (very impressed) and they said they could modify a set of dual port headers for me if I desired. :banana:
i would assume its just replacing the pipe where it splits into 2 ports with a single port design. heres my ideas.. wonder if this will work... are they pretty similar in size and dimensions to the single port? is the dual port flange the only thing stopping it from bolting on?