Need help with exhaust build - Stock M20.

[crappycoco]

Hey,

so I've finally pulled the shitty exhaust job and replaced it with stock. The result is a much quieter car and noticeably lesser throttle response. Plus the sound now sucks =)

I've chopped up the previous exhaust and scavenged the cat and muffler. Don't really care about the muffler - its a magnaflow and i dont know which part number (maybe someone could help with that). The cats number is #336037 (also magnaflow). And AFAIK its CARB compliant. Someone please correct me if I'm wrong, but from searching up that number I get california Carb compliant cats that look like mine =)



Its performance > drone > sound. So I'm really looking for that throttle response that was once there. And I don't want the drone back, because the old setup was really heavy on droning. I don't care about the bassy sound when the car is idling - the only thing I do actually care about sound wise is the raspy tone this engine puts out over 4k rpm - I do miss that. And I think its the high-flow cat =)

Anyhow, I have zero experience with exhaust systems, so please someone school me what each component does to the performance/drone/sound.

Thanks!

[robrez]

'92 BMW 325ic 2.5L CA CARB approved, Magnaflow universal high flow dual in/dual out #36008 $186.45 to your door. Hottexhaust.com 800-288-7730. That part # is not listed on line, must call. to discuss.

[crappycoco]

Um, not sure what you mean by that quote?
I've checked the part number and supposedly it is CARB approved!

I think ill start with just replacing the cat with the highflow one, and go on from there.

[crappycoco]

I've done some research and I ended up more confused than before :nice:

I'm wondering if the huge "catalytic converter" houses the resonator too?
I've seen something resembling a resonator (albeit a really small one) where the O2 screws in.

I'll be swapping the catalytic converter for the high flow one (pictured above) tomorrow and I'd like to know if we need to weld on some resonators too, because i really dont want to be greeted by drone.

Thanks for the help.

[crappycoco]

That swap never happened, bcs the muffler shop owner is a dick =)

Fine, i'll do it myself. I need some info so I don't screw this up guys.
Afaik the stock piping is 1.75" and dual from the engine to the cat where it combines. After the cat it splits again into dual 1.75" right?

My cat is front single 2.75" and back dual 2.25". I'm thinking of getting something like this: http://www.amazon.com/gp/product/B00...=ATVPDKIKX0DER which is dual 2" into single 2.50"

The rear dual pipes of the cat would be directly welded onto the 1.75" stock piping (which is not really round iirc). I would be sticking 1.75" pipes into 2.25" ones - i think its a bit steep, would I need a reducer? Something like this: http://www.amazon.com/OD-2-5-Step-Up...ucer+cone+2%22


Thanks for helping! ;D

[supkev]

https://www.youtube.com/watch?v=S3YXKA04aBk

2.5 single sounds like this. I have other videos on my youtube that gives you a better idea. I love my 2.5 setup, since then I've only added headers.