View Single Post
      01-17-2013, 03:29 PM   #6860
ajsalida
Colonel
ajsalida's Avatar
205
Rep
2,387
Posts

Drives: 95 M3, 02 R1150GSA, 09 335xi
Join Date: Aug 2010
Location: SW USA

iTrader: (2)

From an old supercharger project I worked on, I learned that it takes as much as 4 times the amount of timing to be pulled that caused it in the first place. So that say if the timing were such that at one point there is no detonation, but at 1 deg more there is, the ECU pulls up to 4 deg to stop it. For a lot of reasons mainly detonation cylinder is a lot hotter.

Do not know the algorithm BMW uses but I assure you based on personal experience it is very conservative, pulling a lot of timing out. I think it is a big mistake to think these cars detect octane, they just detect knock/detonation and dial back timing hard whenever they do, and for a long time. You really don't want to rely on this to save your engine running an aggressive tune on lower than recommended octane gas. The problems happen esp. on modded cars where the amount of timing that can be pulled is not enough to stop the detonation on higher boost levels, or at least not soon enough.