Re: Aftermarket Electronic Ignition

["Rick Lackner" <hugacub@whidbey.net>]

> Ok.  The XR-700 uses an infrared beam of light as a signal and this chopper
> blade to make/break the beam which in turn fires the plugs via an electronic
> module.  An "electronic" setup uses an electrical signal from a sensor which
> fires the plugs via an electronic module or on-board computer. I don't know
> of a "big" advantage from one system or the other from a reliability stand
> point.  The electronic system(especially the factory system) may have a
> programmed electronic map to fire the plugs based upon many inputs from other
> sensors in the car and therefore may have better performance.  This of course
> comes with added expense and complexity of the system.  The XR-700 is a
> really good system to replace a points system without the expense of a
> factory system and the complexity.  Obviously this may be at the expense of
> some performance.

I'm not sure which one is better, infared or factory.  The factory 
uses a "hall" sensor.....another  way of saying magnetic or inductive 
pickup.  Trying to think back to my electronic school basics, my 
fuzzy recollection doesn't conjure up big advantages either way, it's 
just a different way to get the same results.  One thing that comes 
to mind is that if infared had any advantage over magnetic, the 
manufacturers would have jumped on it, as the costs are similar.

All the infared or electronic (all ignition systems including points 
are technically electronic) systems do is provide a more accurate way 
of reading the distributor's "bumps" and fire the plugs more 
precisely over a points system.  The methods are very similar and the 
signals sent out from the distributor are essentially the same, just 
cleaner and more precise with any form of electronic ignition.

In other words, all ignition systems perform the same task, telling 
the coil when to send a nice juicy spark to the spark plug.  The 
rotor in the distributor provides the path to the proper spark plug.  
Some systems (electronic) just do a more precise job than others 
(points).

> The points system is limited because it is a mechanical system and there is
> mechanical wear as well as electrical wear(pitting) of the contact.  When it
> "wears", the dwell(the time the points are closed) changes and therefore the
> timing changes.  That's the big disadvantage of a points system.

There's also the consideration of "point bounce", probably the 
biggest reason top end RPMs are limited with a mechanical (point) 
ignition.  The rubbing block of the points is contacted by the 
distributor shaft's bumps (thus the mechanical wear noted above).  As 
the shaft turns faster, the recovery time for the points to close 
again is decreased until the points no longer can close totally 
before they are required to open again and the points "float" and 
you're at top end as far as rpms go.

Now, this is a very simplified explanation and it's late and I don't 
know why I decided to write this.  Keep this in mind when flaming my 
mistakes :)
Rick    
hugacub@whidbey.net
Richard.Lackner@entex.com
85 Scirocco 8V  Wolfsburg
Everett, WA
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