Why Are Spark Plug Wires so Important?

Wires. They’re not exactly exciting, are they? When we talk about performance parts, we usually talk about air intakes, exhaust systems, nitrous kits…anything but spark plug wires. However, spark plug wires are vitally important, and a simple upgrade can make a tremendous difference in performance on an older vehicle and/or a vehicle with other upgrades.

The Anatomy of a Spark Plug Wire

Here’s everything you probably never knew you wanted to know about spark plug wires.

Why Plug Wires Are Kind of A Big Deal

The humble spark plug wire is the communication conduit between your vehicle’s engine timing system (be it electronic or mechanical) and the spark plugs. This signal is vitally important:

  • If the signal to spark isn’t received, the engine misses. You waste fuel and power.
  • If the signal is too early or too late, you lose power and your engine can be damaged.

While it seems like the signal should be carried by the plug wire without incident, spark plug wires aren’t as simple as they seem. First, the wires can become damaged. Second, the wires can “wear” and become less capable of conducting electricity. Thrird, plug wires can create electromagnetic waves that interfere with proper operation.

Not all spark plug wires are equal – the specific type of wire you use on your engine can greatly effect performance. High voltage, high temperature, and highly advanced ignition systems have specific plug wire requirements. If you use the wrong wire (like those cheapo wires that you found on sale at the local auto parts store), they may fail prematurely or fail to perform at higher RPMs.

While you can’t actually add horsepower to your engine by buying a good set of plug wires, you can restore power that’s been lost. A good set of wires can improve idle quality, top-end performance, fuel economy, and even make engine starts faster and easier.

What Makes Up a Spark Plug Wire

All modern spark plug wires have the same basic construction:

  • A center core
  • A conductive suppression layer
  • An insulator
  • A fiberglass braid
  • An outer silicone jacket

If we start from the outside and working our way in, the outer jacket is designed to protect the rest of the from heat, caustic chemicals, and abrasion or pinching during install. Underneath, the braided material both adds strength and minimizes electromagnetic interference (EMI). Then, another insulating layer of dense, heat resistant silicone prevents temperature damage to the core. A conductive suppression layer serves as another mechanism from blocking EMI, specifically radio frequency interference (RFI).

The center core is the heart of it all — it’s the actual conductive material that carries the signal to the spark plug (or to the coil in a coil-on-plug design). The composition of this conductive material can vary greatly; Some cores are conductive carbon wrapped with fine copper wire. Other cores wrap wire around a magnetic material. Cores for older carbureted engines are often made from solid copper or steel wire. While there’s a great deal of debate about the “best” core design, it’s safe to say two things:

The vast majority of plug wires have a conductive carbon element wrapped with wire
Conductive carbon breaks down over time

This means that, in all likelihood, the older your plug wires, the more likely they are to be robbing your engine of power.

Choosing The Best Plug Wires

Choosing the “best” wires is a hotly contested topic. Spark plug wire manufacturers and automotive enthusiasts have strong opinions about the best wires, and there are a lot of conflicting claims about the value of the most popular metric “ohms of resistance per foot.”

Without diving into this debate, here’s the best advice we can offer:

Only buy wires that are designed for your specific application – if you were to install a solid core wire on a new vehicle, for example, you’d have lots of problems with EFI and RFI. Likewise, a wire designed for newer vehicles would fail quickly on an older carbureted vehicle.

Consider buying good wires at least as often as you replace the spark plugs. Since most wires available use a carbon core, and since carbon breaks down every time it carries a charge, replacing an older set of carbon core wires is a quick and easy way to restore some lost performance.

You can find StreetsideAuto’s full selection of spark plug wires and kits here.

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