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Author Topic: The sience of spark plug leads  (Read 5067 times)
Bart_Maztra
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« on: September 10, 2011, 08:22:46 pm »

Just replaced my spark plug wires (HT leads).  Inspired from an article from Oetker on the belgium forum, i didn't went to the store and just bought new ones. No.  I went to the scooter/moped shop and bought some good quality spark plug caps, and some fancy copper/silicon wire.  The spark plug cap have a 5Kohm resistor build in.  As most teenagers don't have much to spend, prices are low in the scooter/moped shop. Payed small euros for caps + wire .  The end which goes in the distributer is cut of the original wire, and soldert to the new wire.



(The way oetker did was using vw spark plug caps, which also have a 5kohm resistor build in, and use copper leads)


But i wonder:  Why does modern wire have a carbon conductor? What's wrong with copper? It seems to me that copper is a better conductor than carbon?  Or what about high performance leads? They have carbon centre with copper or metal coiled around it??  Just try to understand things.
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Jon Weywadt
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« Reply #1 on: September 10, 2011, 09:48:55 pm »

One of the first things I did when I got my car, was to replace the spark plug wires. Thinking I would get the best, I ordered a set from Simons. However, after installing them I found that I would receive an electric chock when touching anywhere on the wire with engine running.  Angry
The insulation was just not good enough. I found that I could buy silicon ignition wires at BilTema.dk. They had built-in resistors and were available in 10 cm increments. These wires are great and no more chocks. They were cheaper than Simons too.  Grin
I have a post with a tool I made to make it easier to seat them on the spark plug.
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Matranaut par excellence Cool
uberprutser
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« Reply #2 on: September 10, 2011, 10:07:58 pm »

Right, scooter parts. Now you've gone to far!!!! Smiley
But I believe they use carbon to reduce electro magnetic interference.

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suffolkpete
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« Reply #3 on: September 11, 2011, 11:09:44 am »

But i wonder:  Why does modern wire have a carbon conductor? What's wrong with copper? It seems to me that copper is a better conductor than carbon?  Or what about high performance leads? They have carbon centre with copper or metal coiled around it??  Just try to understand things.
I think the simple answer is cost.  Copper is very expensive and it is far cheaper to make a lead out of carbon, with in-built resistance, than to make a copper lead and add a separate resistor.  The resistance is necessary to reduce radio interference.  You used to be able to buy a cut-lead suppressor, which is fitted in the lead between the coil and the distributor, instead of using resistive plug caps, but I don't know if they are still obtainable.
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Bart_Maztra
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« Reply #4 on: September 16, 2011, 07:45:16 pm »

Just bought a MSD ignition.  The manual strongly recommend not to use copper.

I spend some time looking for answers.  It seems that carbon wire is reducing interference. And copper not.  But i can't find the answer if there is a difference between a carbon wire and a copper wire with resistor.  All websites i search are not mentioning the effect of the resistor build in the plug.

If i have to do some guessing:
Copper without resistor is making the discharge of the coil to the sparkplug too violent and short?
Adding resistance is reducing the violance (and interference) and lenghtening the discharge/spark?
Is the resistor build in the plug too fragile, and can be distroiyed by many discharges?

Just don't like MSD saying "don't use copper" Now i am affraid using my HT leads. Guess i need to get carbon leads.....
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Anders Dinsen
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« Reply #5 on: September 17, 2011, 07:00:50 am »

Bart, I think MSD recommends against copper leads because they want to avoid electromagnetic interference (EMI). This is not about avoiding ignition noise in your radio, but about making sure your fine MSD ignition module doesn't get "confused" by EMI signals feeding back into the electronics.

MSD modules look great, but I personally find the original Murena electronic igntion system perfectly capable and well performing. The igniton problems I have seen have been due to bad coils and fouled plugs. Some have reported defective ignition modules, so I keep a spare. I've got a box full of fresh NGK plugs and a set in the car so I can replace them when needed.

Why carbon, you ask? EMI is the reason. You don't want noise in the system as that can mess everything up. Further, the resistance in the conductor doesn't matter with the high voltages you're running on the coil. Will an EMI resistor do the same? I honestly don't know, but why bother? - good quality carbon leads last long and work great Smiley

/Anders
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'01 Grand Espace 24v
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Oetker
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« Reply #6 on: September 17, 2011, 11:55:01 pm »

I found some carbon leads have problems with heat.
I use copper leads with 5kohm caps and they do fine.
Some slight interference with weak radiosignals on my radio, but I can liv with that.
EMI is not important for Murena.
Not much computer stuff in there, and the ignition is not digital.
In test I have 2 quality leads from a old Nissan Sunny 95 with carbon leads and two with metal caps from Volkswagen.
The both are running a year on my car now without problems.

The car of Bart has the Mazda engine with more electronics.
In that case try to find the carbon ones to prevent problems with the computer like the original Mazda leads (if they have it).

Also there are sparkplugs and rotors that have build in filters.
« Last Edit: September 18, 2011, 12:08:29 am by Oetker » Logged

I feel like Jonah, only my fish looks different.
Murena 2.2 Red 1982. Murena 1.6 black on places.
michaltalbot
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« Reply #7 on: September 18, 2011, 08:36:46 am »

I ordered a set from Simons. However, after installing them I found that I would receive an electric chock when touching anywhere on the wire with engine running. They were cheaper than Simons too. 

Why this is not surprise for me?  Roll Eyes Everything I bought form Simon was wrong.
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