So (ahem) for the electrically-challenged amongst us, if I understand this correctly you could run the higher resistance plugs without an immediately noticeable change in performance (say you were stranded somewhere and AutoZone (shudder) was the only available place or plugs).
Yes
Longer terms it shortens coil life & point life
No, just the opposite.
and you won't get optimal performance, but you "could" run them for a bit if necessary without, say blowing up your engine or causing irreparable harm, correct?
Yes. Probably won't notice a performance hit until there is plug and point wear. So, with the SOHC4 you would need to address plug replacement and point attention at shorter intervals than book values to maintain performance. (In the instance where too much resistance has been added to the ignition secondary).
At the plug, spark leaps from the sharp edges more readily than the flat, smooth areas, and it takes less voltage to do so. As the plugs wear, there is spark erosion of those sharp edges, making them smooth. To get the same spark activity, a higher voltage is needed to create and maintain the spark intensity and duration of time. So, plugs are more prone to end of life misfires as they get used up and tax the ignition system capability.
With the points, it is all about time, and the ability to charge up the coils. Point surface degradation and rubbing block wear alter the energy storage time of the coils. This timing becomes more critical at high RPMs when time between firing event becomes shorter. This is where to expect misfires or loss of power due to inadequate ignition strength and duration and why the tune up intervals are specified, to keep the engine power near peak levels.
Compare the coil to a bucket of water. The spark plugs dip a ladle full out of it on a regular basis. The resistors in the secondary determine the size of that ladle. RPM is how often the ladle is dipped. The point timing dwell angle, determines how much water is put into the bucket (coil). The goal, of course, is to never let the ladle retrieve less than a full measure.
Traditionally, the spark resistors in the output have been described as reducing Radio interference, which it does, as well as having other benefits.
When current passes through a wire it creates an electromagnetic field around it, in a radiation strength relative to the voltage and current passing through it. Since we need high voltage to jump a spark gap, small changes in the current make a large impact on the radiation strength emanating from the wire. This energy is lost to the ignition circuit and simply thrown away. The resistors reduce the current, which reduces the lost energy. Since the spark is pulsed on a repetitive cycle, the power and frequency can confuse receiver than are sensitive to those frequencies, particularly when the the power arriving from a transmission station is weaker than the power coming from ignition wires.
Traditionally, radio interference was a major concern. However, with the integration of very low voltage computer equipment (some of these devices operate on 1.2v), any wire in proximity to a radiation wire becomes a receiver antenna that absorbs and transfers power to whatever is attached. Noise spikes at computer equipment can either confuse it to make it operate unpredictably, or if the power received is large enough, destroy transistor junctions and render it permanently inoperable.
In this way, ignition resistors provide a dual benefit of improving spark AND protecting nearby sensitive equipment. Both are important considerations.
Hope this helps,
