staticchmbr

how big is the stock 2000 civic si exhaust (diameter)? i am just wondering cause i put on a custom 2.5" pipe all the way back, and it doesnt feel like i am getting too much HP. i was wondering if i should go 2.25"? i didnt know if the stock si exhaust was 2 or 2.25. i also have a custom dual setup to fit my black widow bumper. i know that has a lot to do with the low power gains. is there any way to bump the output a bit?
i hav a dc 4-1 header, oem cat, 2.5" dia resonator, aem intake, skunk 2 im, bbk 70mm tb, and some other stuff which dont have to do with the airflow.

staticchmbr

can anybody help? i have to make an appointment at the shop, and i want to know what i should do. my exhaust is also extremely loud, so i think im going to put another resonator on.

sohc_boy

the dual setup is prolly hurting your low end quite a bit and that 2.5" piping isn't helping either. i'd go with a single 2.25" pipe for your setup. just try ditching the dual setup u have right now since u already have the 2.5" piping made up.

SiRGodfather

The stock Si exhaust is 2" with some serious bottlenecks. Why would you invest in 2.5" exhaust piping when the header you're running only has a 2 1/4" collector? Put the stock IM back on and get a real header (DC Sports is no better than Ractive IMO) that has a 2.5" collector if you want to keep your current set-up. Otherwise ditch the current piping AND the second outlet (which is hurting your exhaust velocity) and get a proper 2 1/4" cat-back where there are no bottlenecks in any of the bends.

NinetyNineSI

dual exhaust will definetly work against you. id recommend just a single outlet setup, 2.25 is fine. keep in mind even if you could fit a 6" exhaust under your car you have to be able to push it all out otherwise again you hurt your HP instead of helping it. other small mods would be a high flow cat, a cat back exhaust ( i have a DC sports stainless cat back 2.25 on my 99 si and love it ) stick with 2.25

hope this helps