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Euro Exhaust Center Section

The Euro exhaust center section compared to the catalyzed unit

I found this picture in the book by Chris Rees titled: "BMW M-Series". It shows a European S14 exhaust center section (non-catalytic) next to a comparable catalyzed version. This makes it easy to compare the two units. There is more going on here than simply the addition of a catalytic converter to the catalyzed system. The blue arrows highlight the two x-pipes. Note that the x-pipe on the Euro exhaust is a completely different fabrication than the catalyzed part. Also note, however, that the all important junction between the secondary pipes occurs at roughly the same place, and that the tube diameters appear to be the same.
Click here for a technical explanation of x-pipes...

Probably the reason that BMW Motorsport developed a new x-pipe for the catalyzed S14 exhaust is that in order to squeeze two separate cats AND a small resonator under the center of the car, it was necessary to angle over towards center much sooner after the x-pipe. The Euro unit, on the other hand, could afford to continue on a straight run after the x-pipe, before angling into a side entrance on the center (large) resonator (shown by the purple arrow). This resonator is probably of similar design to the smaller unit employed on catalyzed systems i.e. two perforated pipes surrounded by wire wool packing - just like the rear muffler.

Click here for a look at a catalyzed S14 resonator cut open...

Also observe that while the catalyzed system has a separate muffler, held on by those pesky crimp-on clamps (which are almost impossible to re-use), the Euro system appears to be all one piece. This is highlighted by the green arrow.

The engine in the background has a couple of neat points as well. The yellow arrow points out the two-hole clamp, which I have seen on the Parts CD but never on any U.S. engine. I haven't really been able to figure out what it's for. The only thing I can think of is that it was intended as a guide for the oil cooler lines as they make their way up to the cooler.

Then the red arrow shows the vacuum hose for the crankcase, which attaches to the rear of the valve cover. On catalyzed E30 M3's this hose goes to an "oil separator" which allows any oil that gets sucked out through the valve cover to return to the sump. But on this engine (presumably Euro-spec) it looks like this vacuum line just routes straight over to the intake plenum. A simpler setup but it allows for the possibility of oil getting sucked into the intake. This is not good for emissions and can promote detonation too from what I've read. Maybe BMW revamped this design later on.



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