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Re: tune up specs

To: Timothy.P.Ronak@akzo-nobel.com
Subject: Re: tune up specs
From: TigerCoupe@aol.com
Date: Fri, 12 Nov 1999 14:11:02 EST
Tim,

My understanding of the purpose of a dual point distributor is that it 
primarily benefits the coil at high RPM.  By increasing total dwell angle, it 
increases coil saturation time, which allows the coil to build a stronger 
magnetic field, producing hotter, higher voltages at the spark plugs.  
Because a dual point distributor does little or nothing to improve 
performance except at very high RPMs, there is no reason to have one unless 
you plan to frequently run your engine in that RPM range.

With a conventional engine ignition system, as engine revs and/or compression 
ratio increase, a coil has less time to produce the required high voltage 
surges.  After each collapse of the magnetic field, adequate time is required 
for the charge to rebuild.  Without enough time it will develop only a 
partial charge, delivering weak spark to the plugs.  In the extreme, the coil 
will become completely saturated and will burn up.  Dual points also usually 
include specially calibrated springs with higher pressure that reduce point 
bounce at high RPM.  

In a Ford dual point, the dwell angle of the two sets of points overlaps by 
7-8 degrees.  During this overlap period the second set of points opens 
before the first set closes, extending the total dwell (coil saturation) 
time.  Ford specs call for setting each point set to 27 degrees, so total 
dwell angle is about 34 degrees (27+7=34).  You recommend setting the second 
set at 32 degrees.  I have not heard of this procedure before and am having a 
little trouble with what it accomplishes.  Could you further elaborate on 
this, please?

Best regards, 
Dick Barker

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