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djcontra 01-10-2004 10:36 PM

E36 TRUE dual exhaust questions...
I was looking at some diagrams of exhaust setups for 95 m3's versus '96-'99 m3's and noticed that the obd1 setup is not in fact a true dual exhaust. There is a Y joint after the cats that the oxygen sensor plugs into, and then another Y that makes the rest of the exhaust dual again. Is this the same on my 1994 325is ? If so, how can I convert it to a true dual exhaust setup without comprimising my o2 sensor's readings? Can I plug it into just one of the exhaust pipes and still get fairly accurate readings?
I'd hate to install my headers, downpipes, free flowing cats, and dual inlet/outlet muffler if there is going to be a Y pipe in the middle of the works.

any help would be greatly appreciated

Quack 01-10-2004 11:05 PM

I have the same setup on my 540i adam, when the 2 cats meet into the y-pipe that's where the O2 sensor goes, after that it's just 1 large pipe all the way to the back, because the pipe is larger after the cat the flow of the exhaust is still free flowing, that 1 pipe is almost as large as the 2 pipes before the cat, so I don't see any compromise there

djcontra 01-10-2004 11:46 PM

Oh well, if I have to, I'll install one of these for the o2 sensor

I'll just hope X-pipe's give the same gains on v6's as they do on v8's :)

Quack 01-10-2004 11:59 PM

that's a pretty big x-pipe, I think you'll be alright

djcontra 01-11-2004 12:03 AM

I hope so. Most likely I'll go that route if I can't get a definate answer.
Also, if anyone is having trouble visualizing what I was explaining (because I can be pretty bad at it sometimes), here's a visual reference of the obd1 m3 exhaust:

Here is another picture of the OBD2 m3 exhaust (notice it has 2 o2 sensors....(must be expensive to replace both :( )

GR8 Ride 01-11-2004 03:22 PM


Originally posted by djcontra
Oh well, if I have to, I'll install one of these for the o2 sensor

I'll just hope X-pipe's give the same gains on v6's as they do on v8's :)

Since when are you running a V6?? :D

Seriously, the OBD-2 system actually runs 4 O2 sensors (2 pre-cat, 2 post-cat), not 2. OBD-I has just one O2 sensor, and you *could* get away with running it on just one side, but here's what I'd suggest doing.

Rather than running an X-pipe, why not build just a pure H-pipe instead, and running the O2 sensor in there? When I built the exhaust for my racecar, I had a bung welded into the cross piece of the H-pipe, and I run it that way. Otherwise it's clear 2.5 inch pipe all the way back (I don't run any cats or mufflers on the racecar).

So you could have a true, dual exhaust, and still run a single O2 sensor (which OBD-I will require).


325iSBimmer 01-11-2004 05:41 PM

1 Attachment(s)
I had asked the same question a couple months agoE36 325iS exhaust]325is exhaust

and didn't really decide on anything....

but now that some body else has brought it up I was thinking I can easily make an H-pipe custom to our cars cause a off the shelf H or X pipe wont work cause they are meant attatch to straigh exhaust systems and ours do a little bend where that single section of pipe is..

I work at an exhaust shop and have a bender and all the equipment to custom make full exhaust systems.....soooo.
If ur interested DjContra I could make 2 H-pipes custom for our cars and we can see how they will work as far as the O2 sensor getting the proper reading.....

im pretty sure putting the O2 sensor in just one of the pipes won't work...and if it does the car probably wont gain anything because it's now getting the wrong reading and the car won't run as effeciently....

djcontra 01-12-2004 12:32 AM

Thanks Pat, I think I'll use your H-Pipe suggestion. Do you have any movies or sound clips of the exhaust on your race car? I've always wanted to hear what an e36 sounds like without cats and a muffler. (and if you can enlighten me, how loud would the car be with just the catalytic converter, resonators, and no muffler?)

325isbimmer: I should be alright for getting an h-pipe made. There are all sorts of exhaust shops along kingston road right near my house, but thanks for the offer. I'm guessing it'll need to be made of high quality steel because of the heat output in that section of the exhaust right?

325iSBimmer 01-12-2004 01:44 AM

yeah....use as thick a stainless steel as you can have bent....
i think we have 14 gauge..... not sure though...just make sure its stainless

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