Let's discuss exhaust tone - The X-pipe.

[gripracer]

The OBD1 6-cylinder E36's have a different exhaust tone than the OBD2 cars. This includes both M and non-M models.

The OBD1 cars have a much more separated-sounding, more defined exhaust pulses (I'm speaking strictly of tone when I say this), and the OBD 2 cars have a much smoother, even-toned sound, closer to a turbine than a VR6, for example.

This characteristic is audible on cars with stock exhausts, as well as cars with a cat-back exhaust.

Personally, while the OBD2 turbine-type sound is nice, and sounds more refined, I find that the OBD1 divided, defined-pulse sound is much more attractive.

Upon looking at the differences in exhaust design between the two cars, it can be noted that there are only a few major differences that could affect tone.





The most significant of them is that the OBD1 exhaust combines its two pipes before the catalytic converters, and the OBD2 exhaust is completely dual all the way back. This leads me to believe that the divided, defined-pulse tone is caused by the exhaust pulses from the first 3 cylinders interacting with the pulses from the last 3. My hypothesis is that the OBD1-sound can be achieved in an OBD2 car by simply installing an X-pipe somewhere along the exhaust system.

Thoughts?

[RobertsRedE36]

We installed an X-Pipe on my son's 1994 325i. At first, we had a major problem. The CEL came on with a 1221 code. After 6 months of debugging and replacing/cleaning parts, we found out that the CEL was just a coincidence! We had a bad computer. Somehow it lost the ability to process the O2 sensor input. After replacing the DME all is well.

We replaced the highly restrictive Y-section of the OBD1 pipe with a 2.5" X-pipe. We had the O2 sensor bung welded into the center top towards the back of the X-pipe. This allows it to sample the stream from both sides of the exhaust. At the same time we put on Magnaflow cats. The exhaust sound is definitely louder and "throatier" even with the stock mufflers.

Some people replace their OBD1 exhaust with an OBD2 exhaust. They weld the single pre-cat O2 bung into one exhaust pipe. I never was a fan of installing the O2 bung on just one side. This sampled only 3 cylinders. If the car is running too rich or too lean on the other side, the engine computer wouldn't adjust or be able to throw the CEL to let you know there was a problem. Of course, you would probably be able to tell there was a problem from a crappy running engine!

Next, we will put on some bolt-in M52 exhaust manifolds.(tubular not cast) We have a set ready to go with new studs, bolts, and gaskets. We may also eventually get a catback or replace the stock muffler with something less restrictive.

One more thing...

Correct me if I'm wrong, but the OBD2 exhaust already has a small "H" in it. It isn't visible in the diagram.

[AllenE36]

One more thing...

Correct me if I'm wrong, but the OBD2 exhaust already has a small "H" in it. It isn't visible in the diagram.

Correct. Its right after the post catalytic converter oxygen sensors:

We replaced the highly restrictive Y-section of the OBD1 pipe with a 2.5" X-pipe. We had the O2 sensor bung welded into the center top towards the back of the X-pipe. This allows it to sample the stream from both sides of the exhaust. At the same time we put on Magnaflow cats. The exhaust sound is definitely louder and "throatier" even with the stock mufflers.

Same thing I did. I cut and welded in a X-pipe to the OBD-II exhaust, deleted the resonators too. Free flowing all the way. It sounds very strong, but only thing I don't particularly like is there is quite a bit rasp mid-range. Reminds me of an S54. They always seem to have rasp.

[gripracer]

that "H" in the OBD2 exhaust looks like a structural thing more than an actual open pipe. are you positive exhaust flows through it?

[jeewing]

We installed an X-Pipe on my son's 1994 325i.

I'd like to see a diagram or (preferably) a picture of the x pipe you used. It seems to me that the angles would present a problem (and where to mount the o2). I'm very interested in doing this on my '94... especially now that we are not required to have smog tests anymore here in NY (OBD-I cars only)

[gripracer]

I'm also interested to see if you guys think my hypothesis about OBD1 vs OBD2 tone is correct, or if you have another theory.

[RobertsRedE36]

I'll see if I can get a picture this weekend. There is room to fit an X-pipe in there before the cats. The exhaust shop cut off about a 2 foot section around the Y-Pipe. They added some extra pipe to the X-Pipe so that it seemlessly fit in the "diagonal" section before the cats.

[AllenE36]

I'm also interested to see if you guys think my hypothesis about OBD1 vs OBD2 tone is correct, or if you have another theory.

Personally I think it has more to do with the motor itself.
Between a OBDI midpipe and OBDII midpipe on my car in stock form I honestly didn't really noticed a smoothness or tone change at all. I think the OBDII midpipe made the exhaust tone a bit louder but that was all.

[gripracer]

Personally I think it has more to do with the motor itself.
Between a OBDI midpipe and OBDII midpipe on my car in stock form I honestly didn't really noticed a smoothness or tone change at all. I think the OBDII midpipe made the exhaust tone a bit louder but that was all.

It can't be the motor, they are much too similar.

Its possible that it's the header design.

[LockDots]

Headers would change the tone a bit, but I'm going to have to side with AllenE36 in that it's mainly the motor. They are very very similar, but still have different displacement and that alone is enough to change the tone.

[Addy325is]

I have a the ob1 but I cut ou the cats and welded in some pipes and have a autoathority muffler .. I really like the sound at first but it's to raspy before 3500 and sounds a bit too ricey for my taste ... Now I wanted to do a bigger and more proper X pipe an I also have aftermarket headers .... Also wanted to know if glasspacks or glassbacks would help with the raspy sound ??

[tlamm]

I really like my X-pipe. Specail made from a M3 middsection. A really nice peice.


It made my car a lot louder and sounds great.

[rllynch1]

^Do you have cats or resonators?

[RobertsRedE36]

I'm also interested to see if you guys think my hypothesis about OBD1 vs OBD2 tone is correct, or if you have another theory.

A number of factors might influence the sound difference between OBD1 and OBD2. The OBD2 exhaust manifolds are freer flowing. Of course, as we know, the OBD1 has the Y-pipe merge and split. Also, the cats and resonators are differently sized and shaped. Finally, the tiny H (if functional) might have some effect too. In short, I just don't know what factor matters the most. I will be installing OBD2 manifolds this summer. I'll try to remember to update how they affect the sound when we do them. In the mean time, I need to listen to more OBD2 exhausts so that I can fully distinguish the difference.

[tlamm]

^Do you have cats or resonators?

Nope just a borla cat-back.

[rllynch1]

Hmm. You should take a video and post it up. I'm interested to see what this would sound like.

[scooper]

When I swapped out my obd1 header (it's for sale) I lost a lot of the burbling and popping on overrun. I replaced it with some SS reps but kept the obd1 midpipe. I want to say I gained some HP up top but I can't say/tell for sure. I didn't do the before and after dyno.

I would say it's the design and shape of the obd1 headers which give the exhaust a nice sound. Friends say I would gain more up top but I also added a chip so...I'm not totally sure. The obd1 headers are crimped (more torque) and are uneven in length and different in shape. If you go with a OBD2 midpipe it's going to sound louder (slightly bigger diameter). Not sure about the flow though...

[tlamm]

Yeah I need to get a video. It sounds ok. Im trying to get a differnt Cat-back but no luck yet.

[atlantisvip]

I did this.. I don't know about sound changing much.. My M3 muffler has always had a perfect deep tone. Its the correct way to do it and no CEL.