^^^ this info is WRONG. The "M50" manifold off the e36 320 is NOT the same part as the one off the the 325 and S50 M3. You'll end up with a major vac leak, I can guarantee it... Source one from somewhere else...
Edit... this mod doesn't work on the 318... unless you've got an OBDii 323, 328, or M3, you c annot swap on the m50 manifold.