In Reply to: Re: What does this diaghram do on 74s? posted by XBeteNoirX on December 23, 1999 at 00:11:23:
: Part number 12 11 1 358 847 is the BMW number for the distributor bellows only. A vacuum bellows can be either one which advances timing or retards timing. Tiis (74+) used a vacuum retard system. At wide open throttle, the advance curves for the mechanical advance distributor and the mechanical advance/vacuum retard distributor are exactly the same. There is no performance advantage to the mechanical (no vacuum) type distributor. The vacuum unit did help with emissions under partial throttle conditions.
: Have a great New Year, Paul.