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BEST SPARK PLUG WIRES

General engine tech -- Drag Racing to Circle Track

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groberts101
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Re: BEST SPARK PLUG WIRES

Post by groberts101 » Wed Mar 06, 2019 12:27 pm

didn't know Scott made 15 ohm/foot wires.. will have to get a custom set made for my little Ford!

David Redszus
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Re: BEST SPARK PLUG WIRES

Post by David Redszus » Wed Mar 06, 2019 1:21 pm

Spark Plug Interference
Control begins with the elimination of the interference sources whenever
possible. Lacking prevention, there are several methods of interference suppression:
ohmic resistance, capacitive reactance, inductive reactance and screening.

Interference suppression using Resistors
Suppression resistors are installed in series, as near as possible to the source of
interference, in order to dampen oscillating voltages and reduce interference energy.
Their secondary purpose is to prevent spark plug wires from becoming antennas
which broadcast interference frequencies.

Interference suppression resistors can be used in circuits with high voltage (and
amperage) such as spark plugs, ignition wires, coils and distributors. They cannot
be used in low voltage systems since their use would cause an excessive voltage
drop and power loss.

Spark plugs
The arc produced when a spark plug fires is the primary source of interference signals.
As the spark arc terminates, unused electrical energy resonates or oscillates at a high
voltage and frequency. These high voltage oscillations backfeed through the wires and
distributor into the coil, broadcasting unwanted noise signals as they go. Spark plugs
are available with internal resistance to help dampen undesirable voltage oscillations.

Distributor caps and rotors
The air gap between the rotor and distributor cap post produces an electrical arc (and
voltage fluctuations) similar to a spark plug. High frequency oscillations will backfeed
into the coil wire and into the coil. This unwanted voltage ringing can be dampened
by use of a rotor with built-in resistance or a resistor type distributor cap.

Spark plug connectors
Similar to spark plugs, spark plug connectors are available with internal resistance,
typically 1K ohm or 5K ohm, to help dampen high voltage oscillations or ringing.
They are particularly useful when resistor type spark plugs are not available in the
correct type and heat range.

Some spark plug connectors are available with metal jackets to act as shields that,
when grounded, dampen the broadcasting of interference frequencies.

Spark plug wires
Since a spark plug wire (or coil wire) will act as a broadcast antenna, it is necessary to
minimize voltage oscillations in the wires which propagate circuit interference. Various
wire designs have been used to dampen voltage fluctuations, including spiral wire
wound conductors and distributed resistance graphite impregnated wires.

Spiral windings do very little more than increase the effective length of the wire and
therefore its resistance value.

Distributed resistance wires also increase resistance by use of a conductor material
with higher resistance. They are often prone to internal breakage due to heat and
vibration, causing multiple arcs and producing their own interference signals. These
small breaks are often intermittent in nature and very difficult to find.

Neither solution is satisfactory for racing and should be removed or not installed.
Multi-stranded copper wire conductors with high dielectric resistance insulation
should be used instead. They are less likely to break internally and total resistance
values can be controlled more accurately.

For inductive type ignitions (either breaker or transistor triggered) total ignition
path resistance should not exceed 15K ohm to prevent loss of spark intensity.

The resistance value of air gaps in the spark plug and distributor cap is on the order
of megaohms, so while resistor suppression of 15K ohm sounds like a high value,
it is of little consequence to firing voltage.

Not so for capacitive discharge ignitions. For CDI type ignitions, the ignition path
resistance should be as low as possible to prevent intolerable current reduction
and loss of spark energy. Therefore, noise suppression by use of resistors is not
possible and any attempt to do so will result in a loss of performance.

Shielded cables
Shielded cables are used to reduce the interference from electical noise. Some electrical
data connections require the use of shielded cables to reduce the noise to signal ratio.
Failure to use the proper type of shielded cable can result in erratic data readings from
the sensor instrumentation.

There are various types of shielded cable available for different applications.

Foil shield cables consist of aluminum foil laminated to a polyester or polypropylene
film. The poly film provides mechanical strength and some additional insulation. The
foil wraps the entire signal wire with no air spaces and provides 100% cable coverage
for electrostatic protection. Foil shields are often used for protection against capacitive
coupling where shielded coverage is more important than low DC resistance.

Braided shield cables consist of groups of tinned or bare, copper or aluminum strands.
One set is woven in a clockwise direction, and interwoven with another set in the opposite
direction.The air spaces between the braided wires allow some penetration of noise
signals. Braided shields provide superior performance against diffusion coupling where
low DC resistance is important, and to a lesser extent, capacitive and inductive coupling.

Spiral shield cables consist of copper wire (usually) wrapped in a spiral around the
inner cable core. The spiral shield is used for functional shielding against diffusion
and capacitive coupling at audio frequencies only.

Combination shield cables consist of more than one layer of shielding. The combination
shield is used to shield against high frequency radiated emissions coupling and
electrostatic discharge. It combines the low resistance of braid with 100% coverage of
foil shields and is one of the more commonly used types of shielded cable.

To be effective, the shielded material must be grounded properly in order to transmit
noise signals to ground and prevent interference with the measured signal.

So what size spark plug wire should be used, 7mm, 8mm, 8.5mm?
The advertised wire dimension refers to the total outside diameter of the wire
but does not indicate the size of the electrical conductor wire inside, nor does it indicate
wire ohmic resistance.

Two methods to determine ohmic resistance are; direct measurement of the wire
without connectors using an ohm meter, and measurement of wire strand size and
number of strands. Once the actual conductor equivalent diameter is known, along
with the material, we can calculate the resistance per foot of wire.

For example, a 19 strand copper wire of .011" diameter is equal to a conductor of
0.0364" and will result in a 30" wire having a resistance of 0.020 ohms. If we add
5 kOhm resistor connectors at each end, we will have a wire with 10,000.020 ohms
resistance. The value to the right of the decimal representing the wire resistance
and to the left, the connector resistor contribution.

Now consider that the air gap at the distributor cap and spark plug gap have a
resistance of a few megaohms. The distributor air gap is usually not adjustable,
but the spark plug gap certainly is. If we consider a spark plug gap of .028"
compared to a gap of 0.060", we see that the required firing voltage will
double; 13 kV to 26 kV, depending on gap air temperature and pressure.

Years ago, every gas station had a scope to examine ignition systems;
now few shops have one. But, a USB scope is both cheap and easy to use and
reveals an incredible amount of very useful information.

maxc
Member
Member
Posts: 176
Joined: Sat Oct 14, 2006 7:57 pm
Location: SE Michigan

Re: BEST SPARK PLUG WIRES

Post by maxc » Wed Mar 06, 2019 1:46 pm

I'm going to try Granatelli wires.

tenxal
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Posts: 536
Joined: Sun Nov 17, 2013 8:48 pm

Re: BEST SPARK PLUG WIRES

Post by tenxal » Wed Mar 06, 2019 4:44 pm

DCal wrote:
Wed Mar 06, 2019 10:06 am
Brian Scott was in his office before and after I was in my office nearly every day. Upon his untimely death my friend (and Brian's best friend) Mark Vieau obtained Scott wires and has done wonders with the business, having re-organized into a modern efficient workplace with 4 fulltime employees and much faster delivery. I think Brian would be happy.
Thanks for the background. They can be proud of a quality product. :)

Firedome8
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Re: BEST SPARK PLUG WIRES

Post by Firedome8 » Thu Mar 07, 2019 4:25 pm

David Redszus wrote:
Wed Mar 06, 2019 1:21 pm
Spark Plug Interference
Control begins with the elimination of the interference sources whenever
possible. Lacking prevention, there are several methods of interference suppression:
ohmic resistance, capacitive reactance, inductive reactance and screening.

Interference suppression using Resistors
Suppression resistors are installed in series, as near as possible to the source of
interference, in order to dampen oscillating voltages and reduce interference energy.
Their secondary purpose is to prevent spark plug wires from becoming antennas
which broadcast interference frequencies.

Interference suppression resistors can be used in circuits with high voltage (and
amperage) such as spark plugs, ignition wires, coils and distributors. They cannot
be used in low voltage systems since their use would cause an excessive voltage
drop and power loss.

Spark plugs
The arc produced when a spark plug fires is the primary source of interference signals.
As the spark arc terminates, unused electrical energy resonates or oscillates at a high
voltage and frequency. These high voltage oscillations backfeed through the wires and
distributor into the coil, broadcasting unwanted noise signals as they go. Spark plugs
are available with internal resistance to help dampen undesirable voltage oscillations.

Distributor caps and rotors
The air gap between the rotor and distributor cap post produces an electrical arc (and
voltage fluctuations) similar to a spark plug. High frequency oscillations will backfeed
into the coil wire and into the coil. This unwanted voltage ringing can be dampened
by use of a rotor with built-in resistance or a resistor type distributor cap.

Spark plug connectors
Similar to spark plugs, spark plug connectors are available with internal resistance,
typically 1K ohm or 5K ohm, to help dampen high voltage oscillations or ringing.
They are particularly useful when resistor type spark plugs are not available in the
correct type and heat range.

Some spark plug connectors are available with metal jackets to act as shields that,
when grounded, dampen the broadcasting of interference frequencies.

Spark plug wires
Since a spark plug wire (or coil wire) will act as a broadcast antenna, it is necessary to
minimize voltage oscillations in the wires which propagate circuit interference. Various
wire designs have been used to dampen voltage fluctuations, including spiral wire
wound conductors and distributed resistance graphite impregnated wires.

Spiral windings do very little more than increase the effective length of the wire and
therefore its resistance value.

Distributed resistance wires also increase resistance by use of a conductor material
with higher resistance. They are often prone to internal breakage due to heat and
vibration, causing multiple arcs and producing their own interference signals. These
small breaks are often intermittent in nature and very difficult to find.

Neither solution is satisfactory for racing and should be removed or not installed.
Multi-stranded copper wire conductors with high dielectric resistance insulation
should be used instead. They are less likely to break internally and total resistance
values can be controlled more accurately.

For inductive type ignitions (either breaker or transistor triggered) total ignition
path resistance should not exceed 15K ohm to prevent loss of spark intensity.

The resistance value of air gaps in the spark plug and distributor cap is on the order
of megaohms, so while resistor suppression of 15K ohm sounds like a high value,
it is of little consequence to firing voltage.

Not so for capacitive discharge ignitions. For CDI type ignitions, the ignition path
resistance should be as low as possible to prevent intolerable current reduction
and loss of spark energy. Therefore, noise suppression by use of resistors is not
possible and any attempt to do so will result in a loss of performance.

Shielded cables
Shielded cables are used to reduce the interference from electical noise. Some electrical
data connections require the use of shielded cables to reduce the noise to signal ratio.
Failure to use the proper type of shielded cable can result in erratic data readings from
the sensor instrumentation.

There are various types of shielded cable available for different applications.

Foil shield cables consist of aluminum foil laminated to a polyester or polypropylene
film. The poly film provides mechanical strength and some additional insulation. The
foil wraps the entire signal wire with no air spaces and provides 100% cable coverage
for electrostatic protection. Foil shields are often used for protection against capacitive
coupling where shielded coverage is more important than low DC resistance.

Braided shield cables consist of groups of tinned or bare, copper or aluminum strands.
One set is woven in a clockwise direction, and interwoven with another set in the opposite
direction.The air spaces between the braided wires allow some penetration of noise
signals. Braided shields provide superior performance against diffusion coupling where
low DC resistance is important, and to a lesser extent, capacitive and inductive coupling.

Spiral shield cables consist of copper wire (usually) wrapped in a spiral around the
inner cable core. The spiral shield is used for functional shielding against diffusion
and capacitive coupling at audio frequencies only.

Combination shield cables consist of more than one layer of shielding. The combination
shield is used to shield against high frequency radiated emissions coupling and
electrostatic discharge. It combines the low resistance of braid with 100% coverage of
foil shields and is one of the more commonly used types of shielded cable.

To be effective, the shielded material must be grounded properly in order to transmit
noise signals to ground and prevent interference with the measured signal.

So what size spark plug wire should be used, 7mm, 8mm, 8.5mm?
The advertised wire dimension refers to the total outside diameter of the wire
but does not indicate the size of the electrical conductor wire inside, nor does it indicate
wire ohmic resistance.

Two methods to determine ohmic resistance are; direct measurement of the wire
without connectors using an ohm meter, and measurement of wire strand size and
number of strands. Once the actual conductor equivalent diameter is known, along
with the material, we can calculate the resistance per foot of wire.

For example, a 19 strand copper wire of .011" diameter is equal to a conductor of
0.0364" and will result in a 30" wire having a resistance of 0.020 ohms. If we add
5 kOhm resistor connectors at each end, we will have a wire with 10,000.020 ohms
resistance. The value to the right of the decimal representing the wire resistance
and to the left, the connector resistor contribution.

Now consider that the air gap at the distributor cap and spark plug gap have a
resistance of a few megaohms. The distributor air gap is usually not adjustable,
but the spark plug gap certainly is. If we consider a spark plug gap of .028"
compared to a gap of 0.060", we see that the required firing voltage will
double; 13 kV to 26 kV, depending on gap air temperature and pressure.

Years ago, every gas station had a scope to examine ignition systems;
now few shops have one. But, a USB scope is both cheap and easy to use and
reveals an incredible amount of very useful information.

https://youtu.be/vOmPW-ze3Tc

Krooser
HotPass
HotPass
Posts: 1481
Joined: Wed Jul 31, 2013 10:14 pm
Location: Tropical Wisconsin

Re: BEST SPARK PLUG WIRES

Post by Krooser » Wed Mar 13, 2019 5:51 pm

My buddy Tom Searing's
Me and Tom Searing Hales Corners Speedway.jpg
Hales Corners sportsman car from 1980-ish with a Mark Vieau-built BBC. That handsome guy holding the flag for a fast time is me....
You do not have the required permissions to view the files attached to this post.
Luxemburg Speedway Hall of Fame Member Class of 2019

DCal
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Posts: 560
Joined: Fri Aug 11, 2006 11:37 am
Location: mooresville nc

Re: BEST SPARK PLUG WIRES

Post by DCal » Wed Mar 13, 2019 6:02 pm

I'll send this photo to Mark. Actually, I'm going to Mooresville tomorrow so I'll take it to him.

Scottperformancewire
New Member
New Member
Posts: 2
Joined: Fri Apr 05, 2019 12:40 pm

Re: BEST SPARK PLUG WIRES

Post by Scottperformancewire » Fri Apr 05, 2019 1:33 pm

To all. This is the first time for me on Speed Talk. I can say with great confidence the information transfer is all quite good.

I am one of two owners of Scott Performance Wire. We have been in business for almost 34 years and our team takes great pride in supplying the best race/performance custom wire sets in the industry. And yes, we do private label wire sets for many "big name" companies. We offer (4) different wire designs at this time, and currently developing a very "low ohm" suppression core wire. All of our suppression core design is coordinated "in house".We supply to all racing/performance venues. We are racers and hot rodders.

To finish, in another time and world I ran several NASCAR engine shops in the area. When leaving NASCAR I chose to get involved in Pro-Stock racing, and even established a facility in the Charlotte, NC area for a very successful team. So today we "build" ignition wire sets and we pursue them with the same passion and vision as we did racing and engine development.

I am open for conversation and look forward to the future with speed talk. Be well, Mark

PS: on a side note. I was very good friends with Don when he worked in NASCAR. I am saddened by his passing. God Bless!

Coloradoracer
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Posts: 525
Joined: Sun Mar 21, 2010 9:48 pm
Location: Lehigh Acres, FL.
Contact:

Re: BEST SPARK PLUG WIRES

Post by Coloradoracer » Sat Apr 13, 2019 9:09 am

tenxal wrote:
Sun Mar 03, 2019 8:27 am
Scott wires are the best wires I've ever used.
As compared to what? Best as in how are they the best?

Not digging, just curious as to what you're comparing to.....
Mark Goulette
Owner/Driver of the Livin' The Dream rear engine dragster
Speed kills but it's better than going slow!
http://www.livinthedreamracing.com
Authorized Amsoil Retailer

Fred Winterburn
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New Member
Posts: 14
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Re: BEST SPARK PLUG WIRES

Post by Fred Winterburn » Thu Apr 25, 2019 7:46 pm

Not sure where this write-up below comes from, but secondary side resistance matters just as much with an inductive ignition as it does with CDI. The physics of energy transfer remain the same in that regard. I recommend keeping the total secondary side resistance less than 10 kohms ( wire resistance, plug resistance, rotor resistance etc) but excluding coil secondary winding resistance (which is designed in). Any more than 10 kohms more than the secondary winding resistance, even with a powerful ignition system, inductive or CDI, is detrimental to spark energy and duration. Fred
David Redszus wrote:
Wed Mar 06, 2019 1:21 pm
Spark Plug Interference
Control begins with the elimination of the interference sources whenever
possible. Lacking prevention, there are several methods of interference suppression:
ohmic resistance, capacitive reactance, inductive reactance and screening.

Interference suppression using Resistors
Suppression resistors are installed in series, as near as possible to the source of
interference, in order to dampen oscillating voltages and reduce interference energy.
Their secondary purpose is to prevent spark plug wires from becoming antennas
which broadcast interference frequencies.

Interference suppression resistors can be used in circuits with high voltage (and
amperage) such as spark plugs, ignition wires, coils and distributors. They cannot
be used in low voltage systems since their use would cause an excessive voltage
drop and power loss.

Spark plugs
The arc produced when a spark plug fires is the primary source of interference signals.
As the spark arc terminates, unused electrical energy resonates or oscillates at a high
voltage and frequency. These high voltage oscillations backfeed through the wires and
distributor into the coil, broadcasting unwanted noise signals as they go. Spark plugs
are available with internal resistance to help dampen undesirable voltage oscillations.

Distributor caps and rotors
The air gap between the rotor and distributor cap post produces an electrical arc (and
voltage fluctuations) similar to a spark plug. High frequency oscillations will backfeed
into the coil wire and into the coil. This unwanted voltage ringing can be dampened
by use of a rotor with built-in resistance or a resistor type distributor cap.

Spark plug connectors
Similar to spark plugs, spark plug connectors are available with internal resistance,
typically 1K ohm or 5K ohm, to help dampen high voltage oscillations or ringing.
They are particularly useful when resistor type spark plugs are not available in the
correct type and heat range.

Some spark plug connectors are available with metal jackets to act as shields that,
when grounded, dampen the broadcasting of interference frequencies.

Spark plug wires
Since a spark plug wire (or coil wire) will act as a broadcast antenna, it is necessary to
minimize voltage oscillations in the wires which propagate circuit interference. Various
wire designs have been used to dampen voltage fluctuations, including spiral wire
wound conductors and distributed resistance graphite impregnated wires.

Spiral windings do very little more than increase the effective length of the wire and
therefore its resistance value.

Distributed resistance wires also increase resistance by use of a conductor material
with higher resistance. They are often prone to internal breakage due to heat and
vibration, causing multiple arcs and producing their own interference signals. These
small breaks are often intermittent in nature and very difficult to find.

Neither solution is satisfactory for racing and should be removed or not installed.
Multi-stranded copper wire conductors with high dielectric resistance insulation
should be used instead. They are less likely to break internally and total resistance
values can be controlled more accurately.

For inductive type ignitions (either breaker or transistor triggered) total ignition
path resistance should not exceed 15K ohm to prevent loss of spark intensity.

The resistance value of air gaps in the spark plug and distributor cap is on the order
of megaohms, so while resistor suppression of 15K ohm sounds like a high value,
it is of little consequence to firing voltage.

Not so for capacitive discharge ignitions. For CDI type ignitions, the ignition path
resistance should be as low as possible to prevent intolerable current reduction
and loss of spark energy. Therefore, noise suppression by use of resistors is not
possible and any attempt to do so will result in a loss of performance.

Shielded cables
Shielded cables are used to reduce the interference from electical noise. Some electrical
data connections require the use of shielded cables to reduce the noise to signal ratio.
Failure to use the proper type of shielded cable can result in erratic data readings from
the sensor instrumentation.

There are various types of shielded cable available for different applications.

Foil shield cables consist of aluminum foil laminated to a polyester or polypropylene
film. The poly film provides mechanical strength and some additional insulation. The
foil wraps the entire signal wire with no air spaces and provides 100% cable coverage
for electrostatic protection. Foil shields are often used for protection against capacitive
coupling where shielded coverage is more important than low DC resistance.

Braided shield cables consist of groups of tinned or bare, copper or aluminum strands.
One set is woven in a clockwise direction, and interwoven with another set in the opposite
direction.The air spaces between the braided wires allow some penetration of noise
signals. Braided shields provide superior performance against diffusion coupling where
low DC resistance is important, and to a lesser extent, capacitive and inductive coupling.

Spiral shield cables consist of copper wire (usually) wrapped in a spiral around the
inner cable core. The spiral shield is used for functional shielding against diffusion
and capacitive coupling at audio frequencies only.

Combination shield cables consist of more than one layer of shielding. The combination
shield is used to shield against high frequency radiated emissions coupling and
electrostatic discharge. It combines the low resistance of braid with 100% coverage of
foil shields and is one of the more commonly used types of shielded cable.

To be effective, the shielded material must be grounded properly in order to transmit
noise signals to ground and prevent interference with the measured signal.

So what size spark plug wire should be used, 7mm, 8mm, 8.5mm?
The advertised wire dimension refers to the total outside diameter of the wire
but does not indicate the size of the electrical conductor wire inside, nor does it indicate
wire ohmic resistance.

Two methods to determine ohmic resistance are; direct measurement of the wire
without connectors using an ohm meter, and measurement of wire strand size and
number of strands. Once the actual conductor equivalent diameter is known, along
with the material, we can calculate the resistance per foot of wire.

For example, a 19 strand copper wire of .011" diameter is equal to a conductor of
0.0364" and will result in a 30" wire having a resistance of 0.020 ohms. If we add
5 kOhm resistor connectors at each end, we will have a wire with 10,000.020 ohms
resistance. The value to the right of the decimal representing the wire resistance
and to the left, the connector resistor contribution.

Now consider that the air gap at the distributor cap and spark plug gap have a
resistance of a few megaohms. The distributor air gap is usually not adjustable,
but the spark plug gap certainly is. If we consider a spark plug gap of .028"
compared to a gap of 0.060", we see that the required firing voltage will
double; 13 kV to 26 kV, depending on gap air temperature and pressure.

Years ago, every gas station had a scope to examine ignition systems;
now few shops have one. But, a USB scope is both cheap and easy to use and
reveals an incredible amount of very useful information.

Fred Winterburn
New Member
New Member
Posts: 14
Joined: Sun Jan 12, 2014 8:17 pm

Re: BEST SPARK PLUG WIRES

Post by Fred Winterburn » Thu Apr 25, 2019 9:15 pm

-More erroneous information in the post is that the distributor gap cannot be compared directly with the spark plug gap as far as voltage is concerned. The plug gap requires a much higher voltage due to compression and other factors while the distributor gap requires a much lower voltage unless the rotor is trimmed (as some used to do way back with weak ignitions and narrow plug gaps to help with fouling). In addition the statement that spiral wound suppression wire only adds extra resistance due to the length of the wire without contributing anything is also false. It is an inductive suppressor. A method that works and has been proven to work, including spark plugs with inductive suppressors. Champion Q series for example mostly used in outboard motors with CDI. I actually run marine inductive suppressor NGK plugs in my Volvo 1800 because they fit and work well with the CDI. Very robust.
-Another point of contention with the post I have is the statement that HT wire resistance can be as high as 15 kohm because the spark gap is in the order of Mohms and therefore 15 kohms is low by comparison. That comparison is as incorrect as apples and oranges. The spark gap, before breakdown is essentially a leaky capacitor which behaves more and more like a resistor as the gap breaks down, to the point where there is almost no resistance across the gap when fully ionized and the spark well underway. Once that happens (and to a certain extent even before breakdown) the series resistance certainly does matter and limits ignition energy proportionately to the resistance. Fred
Fred Winterburn wrote:
Thu Apr 25, 2019 7:46 pm
Not sure where this write-up below comes from, but secondary side resistance matters just as much with an inductive ignition as it does with CDI. The physics of energy transfer remain the same in that regard. I recommend keeping the total secondary side resistance less than 10 kohms ( wire resistance, plug resistance, rotor resistance etc) but excluding coil secondary winding resistance (which is designed in). Any more than 10 kohms more than the secondary winding resistance, even with a powerful ignition system, inductive or CDI, is detrimental to spark energy and duration. Fred
David Redszus wrote:
Wed Mar 06, 2019 1:21 pm
Spark Plug Interference
Control begins with the elimination of the interference sources whenever
possible. Lacking prevention, there are several methods of interference suppression:
ohmic resistance, capacitive reactance, inductive reactance and screening.

Interference suppression using Resistors
Suppression resistors are installed in series, as near as possible to the source of
interference, in order to dampen oscillating voltages and reduce interference energy.
Their secondary purpose is to prevent spark plug wires from becoming antennas
which broadcast interference frequencies.

Interference suppression resistors can be used in circuits with high voltage (and
amperage) such as spark plugs, ignition wires, coils and distributors. They cannot
be used in low voltage systems since their use would cause an excessive voltage
drop and power loss.

Spark plugs
The arc produced when a spark plug fires is the primary source of interference signals.
As the spark arc terminates, unused electrical energy resonates or oscillates at a high
voltage and frequency. These high voltage oscillations backfeed through the wires and
distributor into the coil, broadcasting unwanted noise signals as they go. Spark plugs
are available with internal resistance to help dampen undesirable voltage oscillations.

Distributor caps and rotors
The air gap between the rotor and distributor cap post produces an electrical arc (and
voltage fluctuations) similar to a spark plug. High frequency oscillations will backfeed
into the coil wire and into the coil. This unwanted voltage ringing can be dampened
by use of a rotor with built-in resistance or a resistor type distributor cap.

Spark plug connectors
Similar to spark plugs, spark plug connectors are available with internal resistance,
typically 1K ohm or 5K ohm, to help dampen high voltage oscillations or ringing.
They are particularly useful when resistor type spark plugs are not available in the
correct type and heat range.

Some spark plug connectors are available with metal jackets to act as shields that,
when grounded, dampen the broadcasting of interference frequencies.

Spark plug wires
Since a spark plug wire (or coil wire) will act as a broadcast antenna, it is necessary to
minimize voltage oscillations in the wires which propagate circuit interference. Various
wire designs have been used to dampen voltage fluctuations, including spiral wire
wound conductors and distributed resistance graphite impregnated wires.

Spiral windings do very little more than increase the effective length of the wire and
therefore its resistance value.

Distributed resistance wires also increase resistance by use of a conductor material
with higher resistance. They are often prone to internal breakage due to heat and
vibration, causing multiple arcs and producing their own interference signals. These
small breaks are often intermittent in nature and very difficult to find.

Neither solution is satisfactory for racing and should be removed or not installed.
Multi-stranded copper wire conductors with high dielectric resistance insulation
should be used instead. They are less likely to break internally and total resistance
values can be controlled more accurately.

For inductive type ignitions (either breaker or transistor triggered) total ignition
path resistance should not exceed 15K ohm to prevent loss of spark intensity.

The resistance value of air gaps in the spark plug and distributor cap is on the order
of megaohms, so while resistor suppression of 15K ohm sounds like a high value,
it is of little consequence to firing voltage.

Not so for capacitive discharge ignitions. For CDI type ignitions, the ignition path
resistance should be as low as possible to prevent intolerable current reduction
and loss of spark energy. Therefore, noise suppression by use of resistors is not
possible and any attempt to do so will result in a loss of performance.

Shielded cables
Shielded cables are used to reduce the interference from electical noise. Some electrical
data connections require the use of shielded cables to reduce the noise to signal ratio.
Failure to use the proper type of shielded cable can result in erratic data readings from
the sensor instrumentation.

There are various types of shielded cable available for different applications.

Foil shield cables consist of aluminum foil laminated to a polyester or polypropylene
film. The poly film provides mechanical strength and some additional insulation. The
foil wraps the entire signal wire with no air spaces and provides 100% cable coverage
for electrostatic protection. Foil shields are often used for protection against capacitive
coupling where shielded coverage is more important than low DC resistance.

Braided shield cables consist of groups of tinned or bare, copper or aluminum strands.
One set is woven in a clockwise direction, and interwoven with another set in the opposite
direction.The air spaces between the braided wires allow some penetration of noise
signals. Braided shields provide superior performance against diffusion coupling where
low DC resistance is important, and to a lesser extent, capacitive and inductive coupling.

Spiral shield cables consist of copper wire (usually) wrapped in a spiral around the
inner cable core. The spiral shield is used for functional shielding against diffusion
and capacitive coupling at audio frequencies only.

Combination shield cables consist of more than one layer of shielding. The combination
shield is used to shield against high frequency radiated emissions coupling and
electrostatic discharge. It combines the low resistance of braid with 100% coverage of
foil shields and is one of the more commonly used types of shielded cable.

To be effective, the shielded material must be grounded properly in order to transmit
noise signals to ground and prevent interference with the measured signal.

So what size spark plug wire should be used, 7mm, 8mm, 8.5mm?
The advertised wire dimension refers to the total outside diameter of the wire
but does not indicate the size of the electrical conductor wire inside, nor does it indicate
wire ohmic resistance.

Two methods to determine ohmic resistance are; direct measurement of the wire
without connectors using an ohm meter, and measurement of wire strand size and
number of strands. Once the actual conductor equivalent diameter is known, along
with the material, we can calculate the resistance per foot of wire.

For example, a 19 strand copper wire of .011" diameter is equal to a conductor of
0.0364" and will result in a 30" wire having a resistance of 0.020 ohms. If we add
5 kOhm resistor connectors at each end, we will have a wire with 10,000.020 ohms
resistance. The value to the right of the decimal representing the wire resistance
and to the left, the connector resistor contribution.

Now consider that the air gap at the distributor cap and spark plug gap have a
resistance of a few megaohms. The distributor air gap is usually not adjustable,
but the spark plug gap certainly is. If we consider a spark plug gap of .028"
compared to a gap of 0.060", we see that the required firing voltage will
double; 13 kV to 26 kV, depending on gap air temperature and pressure.

Years ago, every gas station had a scope to examine ignition systems;
now few shops have one. But, a USB scope is both cheap and easy to use and
reveals an incredible amount of very useful information.

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MadBill
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Re: BEST SPARK PLUG WIRES

Post by MadBill » Thu Apr 25, 2019 9:47 pm

Fred Winterburn wrote:
Thu Apr 25, 2019 9:15 pm
Another flaw in the post is that the distributor gap cannot be compared directly with the spark plug gap as far as voltage is concerned. The plug gap requires a much higher voltage due to compression and other factors while the distributor gap requires a much lower voltage unless the rotor is trimmed (as some used to do way back with weak ignitions and narrow plug gaps to help with fouling). Fred
Fred Winterburn wrote:
Thu Apr 25, 2019 7:46 pm

The highlighted words read that trimming the rotor (to a near point presumably) will increase the voltage requirement to cross the gap. Surely it is the opposite?
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Happy is he who can discover the cause of things.

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Re: BEST SPARK PLUG WIRES

Post by Fred Winterburn » Thu Apr 25, 2019 9:54 pm

Different kind of rotor trimming. In context with what I wrote, the type of trimming I was referring to was lopping some of the rotor edge off evenly without making it 'pointy', IE widening the gap to increase the voltage threshold. The opposite of making it pointy which reduces the voltage threshold. Fred
MadBill wrote:
Thu Apr 25, 2019 9:47 pm
Fred Winterburn wrote:
Thu Apr 25, 2019 9:15 pm
Another flaw in the post is that the distributor gap cannot be compared directly with the spark plug gap as far as voltage is concerned. The plug gap requires a much higher voltage due to compression and other factors while the distributor gap requires a much lower voltage unless the rotor is trimmed (as some used to do way back with weak ignitions and narrow plug gaps to help with fouling). Fred
Fred Winterburn wrote:
Thu Apr 25, 2019 7:46 pm

The highlighted words read that trimming the rotor (to a near point presumably) will increase the voltage requirement to cross the gap. Surely it is the opposite?

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Re: BEST SPARK PLUG WIRES

Post by MadBill » Thu Apr 25, 2019 10:08 pm

Ah, got it.

Back in the eighties some GM engines used as much as 0.080" plug gaps. In transport from the factory to the dealer, cars were started and moved a short distance as many as 40 times. In cold weather this led to many plug fouling/no-start issues. The transport drivers found that they could often get them lit off if they popped loose the secondary wire harness from the cap, resulting in around a half inch auxiliary air gap. I presume this meant a higher voltage would build up before any current flowed, thus preventing the charge from dissipating down the now-semiconductive insulator...
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

Fred Winterburn
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Re: BEST SPARK PLUG WIRES

Post by Fred Winterburn » Thu Apr 25, 2019 10:11 pm

Yes, Exactly. The 'booster gap' only works if there is enough available voltage, and GM made sure they had enough. Actually, too much! Fred
MadBill wrote:
Thu Apr 25, 2019 10:08 pm
Ah, got it.

Back in the eighties some GM engines used as much as 0.080" plug gaps. In transport from the factory to the dealer, cars were started and moved a short distance as many as 40 times. In cold weather this led to many plug fouling/no-start issues. The transport drivers found that they could often get them lit off if they popped loose the secondary wire harness from the cap, resulting in around a half inch auxiliary air gap. I presume this meant a higher voltage would build up before any current flowed, thus preventing the charge from dissipating down the now-semiconductive insulator...

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