Aftermarket coils Myth?

[Guest]

Hi,

I was thinking. Why would high performance coils be advantageous on a stock-ish GS that is running good throughout the RPM range. If it only takes lets say 10,000 volts to jump the gap on your spark plugs and your stock coils are capable of putting out out 15,000 volts wouldn't they just spark when you reached 10k volts. If you have high performance coils wouldn't they just jump the gap when the electric potential reached 10K volts also --- yielding the same results?

I can maybe see if one was running high compression pistons and it required say 20,000 volts to jump the gap and they needed coils capable of putting out over that voltage.

Can someone school me on this? Am i thinking right? Wrong? what are you thoughts?

[GSexpress]

Higher voltage also produces higher amperage which makes a hotter more robust spark, ignighting more fuel air in a shorter amount of time, and burn it more completely.. That means that you'll create more pressure for the same amount of fuel air mix. Higher combustion pressure means more power. These coils also are more efficient at saturation time meaning they will recharge and fire better at higher rpms.

[GregT]

When the EPA started mandating leaner mixtures back in the day, a lot of research went into burning these mixtures reliably.
It was found that larger plug gaps were one answer - provided you had the voltage to fire them..hence the introduction of better coils.

As a general rule bigger gaps in conjunction with better voltage cover up a lot of carburation glitches - hard starting is generally cured and I've seen midrange hesitation problems disappear.

As you say, if you have no problems now and are quite happy with what you've got, why change ?

[posplayr]

Hi,

I was thinking. Why would high performance coils be advantageous on a stock-ish GS that is running good throughout the RPM range. If it only takes lets say 10,000 volts to jump the gap on your spark plugs and your stock coils are capable of putting out out 15,000 volts wouldn't they just spark when you reached 10k volts. If you have high performance coils wouldn't they just jump the gap when the electric potential reached 10K volts also --- yielding the same results?

I can maybe see if one was running high compression pistons and it required say 20,000 volts to jump the gap and they needed coils capable of putting out over that voltage.

Can someone school me on this? Am i thinking right? Wrong? what are you thoughts?

I think you are ignoring alot of empirical evidence. Stock ignitions can very often put out very weak yellow sparks at cranking speed. My Accel coils are blue at cranking speed.

Which would you want to fire your charge?

Unless you have a dyno and can measure the exact effect (under all conditions) of the stock coils, it is much cheaper to exceed what you need with after market and not worry about just meeting the requirement.

Excessive design margin is still cheaper than screwing around with an inadequate ignition system that may or may not periodically mis fire.

It is pretty much the first law of hot rodding to get your ignition house in order.

[Colin Green]

When the EPA started mandating leaner mixtures back in the day, a lot of research went into burning these mixtures reliably.
It was found that larger plug gaps were one answer - provided you had the voltage to fire them..hence the introduction of better coils.

As a general rule bigger gaps in conjunction with better voltage cover up a lot of carburation glitches - hard starting is generally cured and I've seen midrange hesitation problems disappear.

As you say, if you have no problems now and are quite happy with what you've got, why change ?

That is very interesting. Thanks Greg. It's all Voodoo to me but still appreciate some of the basic reasoning (when I can grasp it).

Something I can maybe play with if I score some affordable but gruntier coils.

[koolaid_kid]

Nicholas, the coils do not fire when they reach a certain potential, they fire when the signal generator/ignitor tell them to fire. Thus a coil that has enough windings to achieve 30kV will build that potential and wait until given the signal. Then the spark plug will see 30kV across its tip.
The first thing to do is to insure that your stock coils are seeing full system voltage, hence the coil relay mod.

[posplayr]

Nicholas, the coils do not fire when they reach a certain potential, they fire when the signal generator/ignitor tell them to fire. Thus a coil that has enough windings to achieve 30kV will build that potential and wait until given the signal. Then the spark plug will see 30kV across its tip.
The first thing to do is to insure that your stock coils are seeing full system voltage, hence the coil relay mod.

I'm pretty sure it is more complicated that that. An additional factor is the air fuel ratio in the chamber for example. IIRC, a leaner condition has more impedance and requires higher spark and will have a higher voltage depending upon impedance and voltage drops. Richer, is lower impedance and is closer to a short so the voltage is lower.

I have a good reference but I think it as work.

Edit: Well here is the reference but a used copy is $85; I guess I should be more careful with mine although it is in very good shape.

http://www.amazon.com/Doctors-Step-Guide-Optimizing-Ignition/dp/B0026QOKUM

here is a link discussing the book. I bought one of the ignition units and it completely changed the character of my old 79 Dodge 440 motorhome. Although it was about $350 (bought aroudn 2000) It is very high quality and works very well.

http://www.chevelles.com/forums/showthread.php?t=3601

[Nicholaschase29]

Nicholas, the coils do not fire when they reach a certain potential, they fire when the signal generator/ignitor tell them to fire. Thus a coil that has enough windings to achieve 30kV will build that potential and wait until given the signal. Then the spark plug will see 30kV across its tip.
The first thing to do is to insure that your stock coils are seeing full system voltage, hence the coil relay mod.

The coils are connected to ground until the igniter opens the ground circuit at a specific crank angle. This collapses the magnetic field in the outer windings of the coils which builds a potential voltage in the inner windings of the coil which are connected to the spark plug wires. this produces a voltage in the wires which jumps the gap. It is not an instantaneous thing but rather something that occurs over a very small time interval.

If you're comparing two, 3 OHM coils -stock and aftermarket - I think the difference would be the thickness of the wire allowing for more turns in each coil as well as a coil of different length. How this relates to the duration of the spark, energy of the spark, temperature of the spark is what i'm interested in.


Here is something that's kind of interesting:

http://www.cedrat.com/fileadmin/user_upload/cedrat_groupe/Publications/Publications/2003/01/Modelling_of_an_ignition_coil.pdf

[OldVet66]

They just plain run better. When I changed over to the Dyna Green 3 ohm coils it was like night and day. It doesn't load up, idles better and just does everything better (stock except jetting for pipes and pods).

[posplayr]

The coils are connected to ground until the igniter opens the ground circuit at a specific crank angle. This collapses the magnetic field in the outer windings of the coils which builds a potential voltage in the inner windings of the coil which are connected to the spark plug wires. this produces a voltage in the wires which jumps the gap. It is not an instantaneous thing but rather something that occurs over a very small time interval.

If you're comparing two, 3 OHM coils -stock and aftermarket - I think the difference would be the thickness of the wire allowing for more turns in each coil as well as a coil of different length. How this relates to the duration of the spark, energy of the spark, temperature of the spark is what i'm interested in.


Here is something that's kind of interesting:
http://www.cedrat.com/fileadmin/user...ition_coil.pdf

In simply comparing a stock coil to an aftermarket coil like the Dyna the difference is the Dyna high voltage coil has more turns at the same resistance so it creates a higher output voltage for the same +12V. The only way to do that is put more copper in the coil that costs more than the OEM likely does.