The white layer of EDPM is...
The white layer of EDPM is covered with a fiberglass weave to add tension strength to the wire. The EDPM is an excellent electrical insulator. It is protected inside the fiberglass weave as well as inside the silicone.
One thing to pay attention to is the quality of the terminals and their attachments on each end. The terminal is the point on a wire that often gets the most abuse. Use a spark-plug boot removal tool to pull wires off the plugs. This inexpensive tool removes the stresses from the terminals during removal.
Fiberglass sleeves are available for abrasion and heat protection. If you can, check the silicone wrap on the outer layer of the insulation. The thickness here is important to quality, because the thicker the silicone layer, the better the heat resistance.
Low resistance is also a factor in selecting plug wires. A difference in resistance of a few hundred ohms is of little significance, but a difference of a few thousand ohms can make an impact. Carbon-string wires, especially if handled roughly, will have more than just a few thousand ohms of resistance.
The actual wire under the...
The actual wire under the EDPM layer is wound tightly over a fiberglass and/or Kevlar core for strength. The stainless steel wire in this case measures 0.005 inch in diameter. Notice how closely the wire is wound onto the core.
The stranded wires of the past still have their place. They are most often prescribed for use with magneto ignitions and may even be difficult to find. I see no problem with using stranded copper wires on many race cars. Any problems would come from outside your car, unless you use radio communication. Surely, you wouldn't be using electronic traction control. Any electronic devices in your car other than the ignition and tach could be affected when using stranded wires. Interference problems would occur if you ran your race engine in the shop with your wife watching her favorite soap on TV. But then you don't really mind sleeping in the shop. Tell her that is why you spent the money-to get a really comfortable seat for the race car!
One other concern might arise if another car on the track is using computer-controlled electronics. The lack of shielding with your stranded wires could interrupt someone else's computer-controlled electronics (e.g., fuel injection).
This stranded core does two...
This stranded core does two things: It provides a form to wind the wire, and its linear strands make up the greater part of the wire's tension strength.
Now you are ready to go to the race car parts store and buy some wires. Looking at several sets, different brands, and more than a few colors, there are a few more things to be aware of. There is the choice of over-the-top or under-the-exhaust routing of the wires. Headers or cast OE manifolds should make the choice for you. Many times, wires are better protected under headers. OE cast manifolds may require over-the-top routing. What is the difference? Length. Over-the-top wires won't reach around and under headers. My recommendation is that you buy a finished set with all the terminals and boots in place. Unfinished kits are available, but avoid these unless you have the exact terminal installation tool needed or this is what you do on your day job. Poorly attached terminals can disguise a host of problems. These should be a consideration only if you have special needs.
So, get sparked, get wired, and be smart about your choice.
I have found that these companies (among others) make a good-quality spark-plug wire for racing purposes. Construction may vary somewhat, but the overall result should be satisfactory. Choose your wires carefully and pay attention to their inner construction. Wire set quality extends to more than just the wire and its covering. The quality of the terminals, their connection to the wire, and the plug and distributor posts are important features. Selection should be based on quality.