Miata Mailing List: September 1998, Message #249

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Previously on MSD vs J&S, Steven Daniels <stdaniel@mindspring.com> said...

> Can anyone explain the differences (practical and
> fundamental) between the MSD and the J&S knock
> sensor?

The MSD retards timing by a fixed amount proportionate to something (boost
level?)  I think it's MP controlled, but I'm not sure.  The J&S is a knock
sensor which listens for knocking and then retards the spark until it
stops.  I assume it advances it again at some point, but I don't know
exactly how it works as I have neither system.

The long and short of it is that the J&S responds to a problem, whereas
the MSD tries to prevent it without being able to detect it.  The J&S will
allow more advance to be safely run than the MSD.

	-John

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John Freas (jfreas@earthlink.net)
Red '90 Base-ish #7690
Birmingham, AL
Team LS1, SP, the Gap...
Team dlralt, PBC, Roebuck, Voodoo...
"I have no idea what those dimple things on the windshield frame are for."
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