Dick,
As I said it has been a while since I used mechanical points as I made the
transition to electronic ignition ages ago. The process I used for my Accell
dual point distributor was to set the initial points dwell first to 26-28
with the secondary set blocked with matchbook cardboard and then set the
secondary points for a total of 32 degrees (It could have been 34-36...I
just don't remember) so that the total dwell equalled the final dwell. I
preferred to skip the step where I blocked the initial set as it never
worked out to give me the right total dwell by setting them independently to
the 26-28 degrees so I just set the initial and then left them working and
adjusted the secondary set to give me the desired setting for total dwell. I
worked very well up to 7900 RPM.
The process you would use for setting dwell by setting each set
independently would be to set the initial set of points with the secondary
set not installed or with a piece of cardboard insulating the secondary
points so that they do not disrupt the reading when setting the primary set.
Once primary is set block the primary contact points with cardboard and
adjust your secondary set to 28 degrees (or 26 or whatever is called for as
specs) and then remove the card board between the contact points and check
the total. If you are lucky the total will be 34 if not adjust the secondary
set to achieve the desired 34 (...or whatever) degrees.
I think I must have been a little vague Dick about setting the secondary
points to 32 as it reads that I set the secondary to 32 but in fact the
dwell was set to 32 with the combination of both sets of points as the first
set was still generating the 26-28 and I used the secondary set to obtain
the 32-34 desired. If I measured the secondary set it is likely it was
somewhere between 27-29 degrees. Dick you are right, the purpose of the
extra dwell is to increase the amount of time that we deplete the spark from
the coil. As RPM increases the closed point event becomes shorter and
shorter and the extra set of points allows you to still deplete all of the
spark from the coil even at high RPM.
I hope it helps,
Best Regards,
Tim Ronak
-----Original Message-----
From: TigerCoupe@aol.com [mailto:TigerCoupe@aol.com]
Sent: Friday, November 12, 1999 12:11 PM
To: Ronak, Timothy P
Cc: tigers@autox.team.net
Subject: Re: tune up specs
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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