plug gap

bassndeere · Nov 15, 2012

As I understand it, a coil just produces enough voltage to jump the gap on the spark plug. Most antique tractors run .020/.025 gap. What if the spark plugs where changed to the newer style of plugs with a setting of .040/.060? If the coil was capable of 40,000/45,000 volts would it produce more voltage?

Ole Johnny · Nov 16, 2012

Voltage out put of a coul is dependent on the number of turns or windings in the coil itself. If you use a coil with double the internal windings, you would have twice as much voltage output. If you are trying to get more spark, you can get hotter coils and all coils fire when the voltage to them is interupted and the field collapses so a points set or electronic system will do the same job under normal engine speeds.

Anonymous-0 · Nov 16, 2012

And what good will a hotter spark do?

Anonymous-0 · Nov 16, 2012

The voltage output of a coil is directly dependent (up to max capability)on the spark plug , condition, gap, and the atmosphere (compression) that it operates in .IE. if a plug requires 3000v, to arc, then that is what the coil produces for that plug, It would be verry rare for all plugs in an eng to fire at the same voltage
Heat range will have no, to verry little effect on coil output. It does change the tenperature at which the plug operates , which may have a little effect. That temp range is only an indication of the plugs ability to fire in dirty (oily) conditions>

buickanddeere · Nov 16, 2012

A wider plug gap, higher compression and/or exotic fuel requires more voltage to jump the plug gap.
Eventually the spark will jump inside the dist cap instead of across the plugs. One more reason why distributors have disappeared from gasoline engines.

north puller · Nov 16, 2012

A 40000V coil wil not necessarily (or likely) deliver 40000V. You are correct in saying that the coil will discharge its energy when the voltage reaches the point at which it can jump the gap. But what happens to the rest of that 40000V? What happens is the coil discharges its "energy". This is in the form of an electrical circuit which consists of both voltage and current.

Your 40000V coil has 4 times the energy than a 10000V coil. With the same plug gap, they will both discharge at the same voltage, but the 40000V coil will discharge 4 times the energy creating that big fat blue spark.

If your old coil will light off the mixture fine, than you don't need a bigger coil, however, if your old coil is just barely up to the task then a better coil may help.

A larger gap is not for the purpose of creating more spark energy. You want a larger gap to give more room for the flame front to grow. More spark energy is simply a requirement of a larger plug gap. Idealy we would have .100" gaps with tons of room for the flame to start, but problem is that's too hard to jump and you end up with erratic spark fireing sideways to ground, or jumping within the dist cap as Buick said, fireing out the side of the wires, or arcing at the coil tower itself.

Basicly, the higher voltage coil is most likely not necessary, but good insurance if you are buying a coil anyway as a tune up or a 12V conversion.

buickanddeere · Nov 16, 2012

(quoted from post at 13:28:43 11/16/12) A 40000V coil wil not necessarily (or likely) deliver 40000V. You are correct in saying that the coil will discharge its energy when the voltage reaches the point at which it can jump the gap. But what happens to the rest of that 40000V? What happens is the coil discharges its "energy". This is in the form of an electrical circuit which consists of both voltage and current.

Your 40000V coil has 4 times the energy than a 10000V coil. With the same plug gap, they will both discharge at the same voltage, but the 40000V coil will discharge 4 times the energy creating that big fat blue spark.

If your old coil will light off the mixture fine, than you don't need a bigger coil, however, if your old coil is just barely up to the task then a better coil may help.

Your math and understanding of electrical principals needs some work.
If ohms law applied to the ignition coil circuit. The increase from 10,000 to 40,000 volts would not be 4X more power. The power level would actually be 16X higher.
The amount of energy stored in the coil has a fixed max amount. 4 amps at 12 volts . That's all.
Once the spark jumps the plug gap and leave an ionized low resistance path.All the energy in the collapsed magnetic field is going to be dissipated across that gap.

A larger gap is not for the purpose of creating more spark energy. You want a larger gap to give more room for the flame front to grow. More spark energy is simply a requirement of a larger plug gap. Idealy we would have .100" gaps with tons of room for the flame to start, but problem is that's too hard to jump and you end up with erratic spark fireing sideways to ground, or jumping within the dist cap as Buick said, fireing out the side of the wires, or arcing at the coil tower itself.

Basicly, the higher voltage coil is most likely not necessary, but good insurance if you are buying a coil anyway as a tune up or a 12V conversion.

bassndeere · Nov 16, 2012

Thanks for all the advice and guidance. I have been looking at those spark plug adapters to use the new type plugs, which generally run a wider gap. My ignition system is adequate but could always use an improvement/change. Always looking for a bigger bang. Thanks

Anonymous-0 · Nov 19, 2012

(quoted from post at 10:28:43 11/16/12) A 40000V coil wil not necessarily (or likely) deliver 40000V. You are correct in saying that the coil will discharge its energy when the voltage reaches the point at which it can jump the gap. But what happens to the rest of that 40000V? What happens is the coil discharges its "energy". This is in the form of an electrical circuit which consists of both voltage and current.

Your 40000V coil has 4 times the energy than a 10000V coil. With the same plug gap, they will both discharge at the same voltage, but the 40000V coil will discharge 4 times the energy creating that big fat blue spark.

If your old coil will light off the mixture fine, than you don't need a bigger coil, however, if your old coil is just barely up to the task then a better coil may help.

A larger gap is not for the purpose of creating more spark energy. You want a larger gap to give more room for the flame front to grow. More spark energy is simply a requirement of a larger plug gap. Idealy we would have .100" gaps with tons of room for the flame to start, but problem is that's too hard to jump and you end up with erratic spark fireing sideways to ground, or jumping within the dist cap as Buick said, fireing out the side of the wires, or arcing at the coil tower itself.

Basicly, the higher voltage coil is most likely not necessary, but good insurance if you are buying a coil anyway as a tune up or a 12V conversion.

If you have the cap spacing hei or ford cap a msd 6 a box and blaster 2 coil on a 16 volt battery will jump a 1/8 inch plug gap if you have good wires.

plug gap

bassndeere

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bassndeere

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