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Old 02-04-2006, 06:36 PM   #28
JackG
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Join Date: Mar 2005
Location: South Carolina
Posts: 530
Quote:
Originally Posted by MNBoxster
A Knock Sensor is really a sort of microphone and when it picks up the sound from a knocking Cylinder, the DME retards the Spark, that is, makes the Spark occur earlier in the Engine Cycle to control the detonation of the Fuel. You can retard the timing only so much on an Engine. and in this case, it does so sufficiently to use 89 Octane Fuel. The downside to this is that when you retard the Spark, you also reduce the Power the Engine can make (in this case, somewhere in the neighborhood of 5-8HP).
Just a quick correction...

Retarding the spark actually makes it happen *later* in the cycle, not earlier. The earlier the spark happens, the more *advanced* the spark is.

Just didn't want anyone to go down the wrong path based on this...

Jack
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