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Re: dwell adjustment

To: datsun-roadsters@autox.team.net
Subject: Re: dwell adjustment
From: "John F Sandhoff" <sandhoff@csus.edu>
Date: Tue, 10 May 1988 19:02:42 PST8PDT
Random mumblings:
> I can not use my dwell meter anymore because of the MSD ignition. 

> ... what if you 'ovalized' the two mounting holes in the pertronix unit??

Dwell doesn't count (much?) with electronic ignitions.

The purpose of dwell is to set up enough time for the magnetic field
to build within the coil. When the points OPEN, the field collapses and
induces a high voltage spike in the secondary's turns and turns of
wire. The bigger the field that collapses, the more energy. The longer
the points stay closed, the bigger the field. [left for someone with more
knowledge than me: why 'more dwell is better' is NOT the case]

Electronic ignitions like the MSD don't require this 'buildup'. All they
care about is a TRIGGER. The points opening tell the unit WHEN to set
off the spark. There is no buildup time provided by the points being
closed, as the points do not provide the current flow thru the coil. They
simply tell the electronics when to fire.

Now, I may be wrong on the Pertronix, but I'll jump in anyway :-)
My understanding is that the Pertronix is just an electronic switch that
determines WHEN to go off. There is no 'open-close' cycle with a
Pertronix  - just a PULSE that says 'now!'. So there is no dwell to speak
of (well, the dwell is pre-set by the internal electronics and not
its physical proximity to the cam lobe).
Someone that knows pertronix engineering can correct me :-)

-- John
     John F Sandhoff   sandhoff@csus.edu   Sacramento, CA

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