swingtan
17-11-2008, 06:20 PM
Over the past few weeks there have been a few posts regarding ignition leads. There have been the usual questions, like "Which is best", "How long do they last" etc and while the answers have usually been given, the reasons behind the answers are lacking a bit. So I thought it was time to get together some information on ignition leads.
http://farm4.static.flickr.com/3169/3037596832_86b305b8f4.jpg
Background
The ignition lead has only one role, to conduct the high voltage ignition pulse from the coil to the spark plug. It must do this without the voltage "leaking" out of the lead and without interfering with other systems in the car. The main components are a central conductor, surrounded by an insulating jacket, with connectors at each end. The connectors also have an insulating "boot" to prevent voltage leaks and keep the connectors clean. All Ignition leads take this basic form.
http://farm4.static.flickr.com/3139/3037596470_94885bfacf.jpg
Original Leads
When the first internal combustion engines were made, the amount of energy produced for the ignition sparks was quite small. So the first leads were made to transfer the maximum amount of energy to the spark plugs. To do this, leads made of copper wire were used and these were basically the same are any other wire. The only real difference to a normal electrical wire was the thickness of the insulation. The higher voltage needed a thicker insulation. Up until the 60's and even 70's, copper ignition leads were the norm.
http://farm4.static.flickr.com/3013/3036759679_5a57a23734.jpg
As technology developed, the available power for the ignition system grew to the point where the there was a lot more "spark" power available than was really necessary for the average daily driver. The additional spark power started causing a side effect in the ignition system, it would interfere with things like radios when they were in or close to the car. The reason for this was that when a spark plug "fired", there was not only a spark at the plug, but also in the distributor. When a spark is created, a by product is that it produces radio waves, lots of them and at all different frequencies. So the ignition system could be heard in just about any radio near the car. A good test for this for the Melbourne members is to tune to an AM band station why you are next to a tram.
The initial fix for this was to place a resistor in the ignition lead, to reduce the power.
http://farm4.static.flickr.com/3028/3037596100_3f9267651b.jpg
These appeared in the 50's and 60's, when car radios were first making a big show. There were 2 main types back then...
In Lead: as in the picture, where you cut the lead and the resistor screwed into the cut ends.
Pluggable: where they acted like a "plug adapter" and plugged into the distributor cap while the lead plugged into the resistor.
Both versions worked as good as each other, which was not great. But they did allow you to listen to the radio. Here's a couple of close ups of a "screw in" adapter.
http://farm4.static.flickr.com/3152/3037595774_0018bfd926.jpg
http://farm4.static.flickr.com/3280/3036758937_1638298880.jpg
The biggest problem with these was that they let dirt and moisture in and reduced the effectiveness of the lead as a whole. They also provided additional areas for the high voltage to "leak" out, resulting in misfires. Another point with the copper leads was their ability to "induce" a voltage in leads that ran next to each other, so a spark on one lead could cause a spark in an adjacent lead, this was know as a "cross fire". We then had some significant progress.
Silicon Suppression Leads:
With new materials and processes developed in the late 60's and 70's, we saw the introduction of the Silicon Suppression leads. FWIW, the "silicon" had nothing to do with the "suppression". The silicon was used in the insulation material as it did a far superior job to plastic. It with stood higher temps and could handle much higher voltages. The "suppression" part of the lead was due to the construction of the conductor moving away from copper, to a carbon impregnated media. This allowed the leads to have an "inbuilt" resistance that progressed along the entire length of the lead. It had no joins and was also more flexible than copper.
http://farm4.static.flickr.com/3049/3037595406_ed78e7ecb8.jpg
Above you can see the construction of the Silicon Suppression lead, it has...
An outer insulation jacket that protects the inner insulation from abrasion. (yes, this a genuine VN 5lt ignition lead ).
Nylon reinforcement for the silicon insulation.
The silicon insulation
The carbon conductor, which is a very thin layer over a central strengthening core
The nylon core, which is just there to strengthen the lead.
These leads were a great lead and were the reason that many of the big names in consumer automotive products got a name for themselves. They were a great step up from copper leads and did a very good job. However they did suffer from the carbon layer breaking down over time, resulting in miss fires. They also still reduced the spark power by resisting the voltage in the spark. As engine development increased, a better lead was needed.
Inductive Stainless Steel Core
So we get to the current "standard" breed of ignition leads. These leads are not new by any means. They have been used on things like piston aircraft for many years and I've used them for at least the past 20 years. They are known under the terms...
Inductive
Helically Wound
Magnacore
To name just a few. They all work the same and achieve excellent results. They have the best of the copper leads, in that they don't "resist" the voltage and they also suppress radio frequency (RF) noise very well. The modern leads also use high quality fittings to further improve on the lead performance. Here's the and of a "Magnacore" brand lead that is now over 15 years old...
http://farm4.static.flickr.com/3208/3036758595_32618210b9.jpg
Now these leads are not cheap, but they are worth every cent. Because of the price, I'm not going to cut up a lead to show the construction and I don;t have a damaged lead around. Even though the lead above is over 15 years old, it's still as good as new except for it being a bit dirty. Here's the back of the socket end where you can see the end of the central core.
http://farm4.static.flickr.com/3208/3036758401_5ceb513726.jpg
The lead actually looks a lot like the Silicon Suppression lead, but the central core differs significantly. In stead of a "carbon impregnated" layer, these leads have a stainless steel wires that runs in the centre of the lead. So like the copper lead, being a metal, it has a very low resistance compared to the silicon suppression lead. It also indicates why the leads last so long, as the central conductor can't break down. The wire is circled in the picture above and if you look carefully, you'll notice it is "wound around" the central core. Here's a close up showing the coiling, though not a great shot.
http://farm4.static.flickr.com/3162/3036758251_9e483c6f57.jpg
The reason for the "winding" of the wire is to increase the "inductance" of the lead. The electrical guys will know what's coming up, but for those not in the know, an inductor will pass low frequencies easily, but resist high frequencies. So what these leads do is pass the low frequency power of the spark with little resistance, but reduce the radio frequencies very well. So you get a maximum amount of spark power with little or no RF interference. These leads also have a big advantage in that they reduce plug tip erosion by reducing the higher frequency components of the spark.
So now you know why ignition leads are the way they are, you can make an educated choice on the brand of leads you want. Given that all the modern leads are of the Inductive type, there isn't a lot to separate them. The things you may look at are the insulation or jacket thickness, as the more insulation you have, the less chance of spark leaking through. For the stock coils, the stock leads have plenty of insulation. For that matter, the stock coils also have plenty of spark producing power as well. If you install some sort of ultra special coil set up that produces a huge amount of power, you may need thicker leads. But the stock units are pretty hard to beat.
Hope this gave some insight.
Simon.
http://farm4.static.flickr.com/3169/3037596832_86b305b8f4.jpg
Background
The ignition lead has only one role, to conduct the high voltage ignition pulse from the coil to the spark plug. It must do this without the voltage "leaking" out of the lead and without interfering with other systems in the car. The main components are a central conductor, surrounded by an insulating jacket, with connectors at each end. The connectors also have an insulating "boot" to prevent voltage leaks and keep the connectors clean. All Ignition leads take this basic form.
http://farm4.static.flickr.com/3139/3037596470_94885bfacf.jpg
Original Leads
When the first internal combustion engines were made, the amount of energy produced for the ignition sparks was quite small. So the first leads were made to transfer the maximum amount of energy to the spark plugs. To do this, leads made of copper wire were used and these were basically the same are any other wire. The only real difference to a normal electrical wire was the thickness of the insulation. The higher voltage needed a thicker insulation. Up until the 60's and even 70's, copper ignition leads were the norm.
http://farm4.static.flickr.com/3013/3036759679_5a57a23734.jpg
As technology developed, the available power for the ignition system grew to the point where the there was a lot more "spark" power available than was really necessary for the average daily driver. The additional spark power started causing a side effect in the ignition system, it would interfere with things like radios when they were in or close to the car. The reason for this was that when a spark plug "fired", there was not only a spark at the plug, but also in the distributor. When a spark is created, a by product is that it produces radio waves, lots of them and at all different frequencies. So the ignition system could be heard in just about any radio near the car. A good test for this for the Melbourne members is to tune to an AM band station why you are next to a tram.
The initial fix for this was to place a resistor in the ignition lead, to reduce the power.
http://farm4.static.flickr.com/3028/3037596100_3f9267651b.jpg
These appeared in the 50's and 60's, when car radios were first making a big show. There were 2 main types back then...
In Lead: as in the picture, where you cut the lead and the resistor screwed into the cut ends.
Pluggable: where they acted like a "plug adapter" and plugged into the distributor cap while the lead plugged into the resistor.
Both versions worked as good as each other, which was not great. But they did allow you to listen to the radio. Here's a couple of close ups of a "screw in" adapter.
http://farm4.static.flickr.com/3152/3037595774_0018bfd926.jpg
http://farm4.static.flickr.com/3280/3036758937_1638298880.jpg
The biggest problem with these was that they let dirt and moisture in and reduced the effectiveness of the lead as a whole. They also provided additional areas for the high voltage to "leak" out, resulting in misfires. Another point with the copper leads was their ability to "induce" a voltage in leads that ran next to each other, so a spark on one lead could cause a spark in an adjacent lead, this was know as a "cross fire". We then had some significant progress.
Silicon Suppression Leads:
With new materials and processes developed in the late 60's and 70's, we saw the introduction of the Silicon Suppression leads. FWIW, the "silicon" had nothing to do with the "suppression". The silicon was used in the insulation material as it did a far superior job to plastic. It with stood higher temps and could handle much higher voltages. The "suppression" part of the lead was due to the construction of the conductor moving away from copper, to a carbon impregnated media. This allowed the leads to have an "inbuilt" resistance that progressed along the entire length of the lead. It had no joins and was also more flexible than copper.
http://farm4.static.flickr.com/3049/3037595406_ed78e7ecb8.jpg
Above you can see the construction of the Silicon Suppression lead, it has...
An outer insulation jacket that protects the inner insulation from abrasion. (yes, this a genuine VN 5lt ignition lead ).
Nylon reinforcement for the silicon insulation.
The silicon insulation
The carbon conductor, which is a very thin layer over a central strengthening core
The nylon core, which is just there to strengthen the lead.
These leads were a great lead and were the reason that many of the big names in consumer automotive products got a name for themselves. They were a great step up from copper leads and did a very good job. However they did suffer from the carbon layer breaking down over time, resulting in miss fires. They also still reduced the spark power by resisting the voltage in the spark. As engine development increased, a better lead was needed.
Inductive Stainless Steel Core
So we get to the current "standard" breed of ignition leads. These leads are not new by any means. They have been used on things like piston aircraft for many years and I've used them for at least the past 20 years. They are known under the terms...
Inductive
Helically Wound
Magnacore
To name just a few. They all work the same and achieve excellent results. They have the best of the copper leads, in that they don't "resist" the voltage and they also suppress radio frequency (RF) noise very well. The modern leads also use high quality fittings to further improve on the lead performance. Here's the and of a "Magnacore" brand lead that is now over 15 years old...
http://farm4.static.flickr.com/3208/3036758595_32618210b9.jpg
Now these leads are not cheap, but they are worth every cent. Because of the price, I'm not going to cut up a lead to show the construction and I don;t have a damaged lead around. Even though the lead above is over 15 years old, it's still as good as new except for it being a bit dirty. Here's the back of the socket end where you can see the end of the central core.
http://farm4.static.flickr.com/3208/3036758401_5ceb513726.jpg
The lead actually looks a lot like the Silicon Suppression lead, but the central core differs significantly. In stead of a "carbon impregnated" layer, these leads have a stainless steel wires that runs in the centre of the lead. So like the copper lead, being a metal, it has a very low resistance compared to the silicon suppression lead. It also indicates why the leads last so long, as the central conductor can't break down. The wire is circled in the picture above and if you look carefully, you'll notice it is "wound around" the central core. Here's a close up showing the coiling, though not a great shot.
http://farm4.static.flickr.com/3162/3036758251_9e483c6f57.jpg
The reason for the "winding" of the wire is to increase the "inductance" of the lead. The electrical guys will know what's coming up, but for those not in the know, an inductor will pass low frequencies easily, but resist high frequencies. So what these leads do is pass the low frequency power of the spark with little resistance, but reduce the radio frequencies very well. So you get a maximum amount of spark power with little or no RF interference. These leads also have a big advantage in that they reduce plug tip erosion by reducing the higher frequency components of the spark.
So now you know why ignition leads are the way they are, you can make an educated choice on the brand of leads you want. Given that all the modern leads are of the Inductive type, there isn't a lot to separate them. The things you may look at are the insulation or jacket thickness, as the more insulation you have, the less chance of spark leaking through. For the stock coils, the stock leads have plenty of insulation. For that matter, the stock coils also have plenty of spark producing power as well. If you install some sort of ultra special coil set up that produces a huge amount of power, you may need thicker leads. But the stock units are pretty hard to beat.
Hope this gave some insight.
Simon.