Learning, Wiring,

Are Spark Plug Wires Universal? (3 Types of Wires and 4 Differences)

Are you looking to use spark plug wires and not sure if you can use any type for your car?

No, sparkplugs are not universal. Spark plug wires actually come in all sorts of different lengths, diameters, and configurations to fit specific engines and vehicles. It’s really important to make sure you’re using the correct spark plug wires for your particular engine to be sure you’re getting the best performance possible and to avoid any potential issues.

The biggest difference between spark plug wires is the component sizes and core types. The component sizes determine whether the spark plug is compatible with your engine socket, while the core types control the power output and EMI/RFI suppression.

Learning about these differences is essential when tuning up your car’s engine.

Difference in Components

10 spark plugs
Video | ChrisFix

Matching the spark plug size with your engine’s socket is crucial. The main difference between spark plug wire sets is the difference in diameter and length between the components – particularly the cylinder head specifications.

There are four things to keep in mind about the cylinder head’s specifications:

1. Thread Pitch

The thread pitch refers to the size of the threads. A fine thread pitch is thinner and has a higher thread count, while coarser types have thicker but fewer threads going around the spark plug.

Most spark plugs for vehicles have a thread pitch of 1.25 mm – measured from the peak to the peak of each thread. 

2. Diameter

The spark plug diameter is measured around the widest part of the threaded section, including the threads themselves. The diameter is always rounded up, so a 12.7 mm wide spark plug is classified as a 13 mm one. 

3. Reach

Reach is the spark plug length from the ground electrode (the metallic hook-like structure) to the gasket (the base of the threaded section). Spark plugs generally have the same reach, so it’s not typically included in most spark plug specifications. 

4. Hex Size

Hex refers to the bolt-like structure on your spark plugs. The hex size must correspond to the size of the socket you’re inserting it into.

Most spark plugs come in a 16 mm wire (5/8 inches) and 21 mm wire (13/15 inches) hex size. However, there are smaller or larger versions available for specific usage. 

Different Spark Plug Core Wires

man holding 2 spark plugs
Video | ChrisFix

Most people are unaware of different types of spark plug cores; the core wire is inside the spark plug wire. Unlike the components above, it isn’t visible to the naked eye. The core wire type primarily determines the performance of spark plug quality.

Some core types offer lower resistance, allowing more engine current flow. At the same time, others have better EMI (Electro-Magnetic Interference) or RFI (Radio Frequency Interference) suppression, which controls the electric field produced when currents run through the spark plug. 

Don’t worry if it seems too complicated; we’re here to explain the key differences between each core type.

According to the National Automotive Parts Association, there are three primary core wire types in use:

Carbon Core

If you plan to replace your car’s spark plugs, you’re probably looking for carbon-core wire sets. 

Carbon cores are mostly used for vehicles due to their balance between EMI/RFI suppression and high resistance. The EMI/RFI suppression is the main reason you can use radios, car audio GPS systems, and other electronics in your car. Carbon cores can suppress the electrical field created by the engine and prevent it from interfering with nearby electronics. 

Solid Core  

You’ll need a solid-core spark plug if you need more power and don’t care about the car’s stereos and radio. 

Solid core wires deliver more current at the cost of higher EMI. It’s mostly used for powerful engines like those used in race cars or vintage cars that still use magneto-style ignition systems (those that need carburetors and points) like the big block crate engine. 

Spiral Core

If you’re an enthusiast who wants to fine-tune your engine, you’ll be interested in spiral cores. 

Spiral core uses modern technology to create a specialized alloy with low resistance but superior EMI/RFI suppression. Because of this, many enthusiasts and professionals prefer to use spiral core wire sets; however, they can be expensive. Still, the price is well worth it if you plan to invest in your vehicle. 

Video Reference


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About Sam Orlovsky

AvatarCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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