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Blackout
11-06-2005, 10:03 AM
im building a custom exhaust for my 635csi. from the manifold, it splits into 2 downtubes, one from the front 3 cyclinders and one from the back 3. it came stock with a 2-1pipe then the oxygen sensor before the cat. now, it continues with 2 pipes, one to each side of the car. with no cat, resenator or muffler. where should i put the oxygen sensor. i only have one so which pipe should it be on. the one that comes from the front 3 or the back 3? will i have enough backpressure for the car to run because there wont be any muffler, cat or resonator?

Jari
11-06-2005, 06:12 PM
I had the same problem when I put in dual exhaust. I ended up welding a small h-pipe up front and mounted the O2 in there. I don't think you want your o2 reading only one bank of cylinders.

Justin e36
11-06-2005, 10:44 PM
Yeah.. I've been thinking this over and I'm still not sure how to answer it. I don't know if the o2 sensor will give a proper reading from only 3 cylinders. I guess in theory it shouldn't matter which ones you choose. But as mentioned, you might want a reading on all 6 cyl's..

ZiMMie
11-06-2005, 10:53 PM
i dont think it matter, because most headers i have seen for the e30 have the O2 sensor port for only 3 cylinders..(first 3 cylinders)

https://secure9.nexternal.com/ireland/images/header%20e302.jpg

MarkD
11-07-2005, 08:29 AM
i dont think it matter, because most headers i have seen for the e30 have the O2 sensor port for only 3 cylinders..(first 3 cylinders)

https://secure9.nexternal.com/ireland/images/header%20e302.jpg

That's correct, it does not matter as the other bank is running the same way, unless you have different sized injectors in there, (which you wouldn't have)

I wouldn't add an H pipe or other crossover pipe as it can cause interference between the two banks, which you don't want.

MarkD

Blackout
11-07-2005, 05:33 PM
ok thanx. ill just put on the first three.

if i dont put on the cat or a muffler or a resonator will i have enough backpressure to run or does it matter?

MarkD
11-07-2005, 05:39 PM
ok thanx. ill just put on the first three.

if i dont put on the cat or a muffler or a resonator will i have enough backpressure to run or does it matter?


If you remove all of them, you most likely need to richen up the mixture at WOT.

98technom3
11-07-2005, 08:05 PM
its not correct in the fact that they will all run the same due to them having injectors. Because if one injector fails all the others will still be fine....therefore they cant all run the same. But just stick with how the aftermarket headers for those would be. Having the O2 on the first 3.

98technom3
11-07-2005, 08:07 PM
If you remove all of them, you most likely need to richen up the mixture at WOT.


agree. otherwise you can actually lose power

Jari
11-08-2005, 12:11 AM
Mark D how exactly does welding an H-pipe cause interference?