spark plug wires

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ericjon262
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spark plug wires

Post by ericjon262 »

I've recently started thinking about spark plug wires, and their affect on vehicle performance, and have started thinking along a new line of thought, low resistance isn't necessarily good, of course excessively high resistance wouldn't help either.

basic concepts:
Volt(V)=electrical potential
current(I)=the flow of electrical charge, measured in amperes.
ampere(A)=1 coulomb passing a point in 1 second
ohm(R)=resistance required for 1 volt to produce 1 amp of current
energy(E)=the ability of a system to do work. measures in joules
Joule(J)= energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second
ohms's law

I=V/R

if voltage stays constant, and resistance goes down, then current has to go up. is this an advantage though? as previously defined, current is the flow of electrical charge, a rate. if the rate goes up, then the time to move the same amount of charge must go down. therefore a lower resistance wire will produce a shorter duration spark.

now heres where things get interesting, the energy of the spark will go up, with the lower resistance wire,

E=CV, or E=V^2/R

here we can see that the heat of the spark will also go up. so now the question, is the hotter spark more desirable, or the longer duration.

I believe the highest resistance(with some "buffer room" for environmental factors) that will still cause the air/fuel mixture in the combustion chamber to ionize and ignite is going to produce a better result than just a shorter hotter spark, but, this discussion also assumes the voltage output from the coil is constant as well, if I had to guess, I would say that the moment the magnetic field in the primary coil begins to collapse, the the voltage on the secondary is going to rise very rapidly, as an almost vertical line, and then have a sharp peak as the mixture is ionized and the arc across the plug stabilizes. After the arc forms the voltage would remain steady for some period, and then slowly drop until the arc can no longer be maintained.

please excuse my crappy exaggerated paint graph...

Image

I don't have the equipment or time to do any real tests ATM, but I would like to hear your thoughts.
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The Dark Side of Will
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Re: spark plug wires

Post by The Dark Side of Will »

There's a lot of info on spark profiles out there. CD ignition systems "ring" and produce multiple sparks of reversing polarity thanks to the interaction between the capacitor and coil to create an RLC circuit.

Two things you need to consider:
The spark plug wire is a small resistance compared to the plug gap, at least prior to the gas in the plug gap ionizing. I don't know what the resistance of the ionized plug gap is right off. IOW, the resistance of the plug wire is not the big factor affecting the circuit.

The *energy* delivered by the coil is the same through a high resistance plug wire or a low resistance plug wire. A high resistance wire dissipates a *TINY* amount more energy than a low resistance wire, but since most of the voltage drop occurs through the plug gap, that's where most of the coil's energy shows up. Since the energy delivered is constant, if the time over which that energy is delivered is constant, then the average power is constant. That means that a lower resistance will actually cause the coil to deliver a lower voltage as well as a higher current.
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