FAQ – Spark Plug Wires 101

FAQ – Spark Plug Wires 101


Spark Plug Wires are some of the most common upgrades for most of our customers, and yet it’s one of the components we receive the most amount of questions about. What is the best style of performance spark plug wire? What size wire do I want / need? 8.5mm? bigger? smaller?

We tackle most of these subjects and questions here in our Spark Plug Wire FAQ 101. Enjoy!

The purpose of spark plug wires sounds simple enough, transferring energy to delivery spark to the plugs and suppress the Electro Magnetic Interference (EMI) that the spark voltage can create. The difference in EMI emissions stems from the level of resistance in the spark plug wire itself.



Too much resistance can decrease the spark energy that will ultimately diminish the spark plug gains you might otherwise be gaining. While too little resistance can cause EMI noise that could make your driving experience a much more noisy one as the high EMI can interfere with the operation of other electronics on your vehicle, like your radio and speakers.

How to Test My Spark Plug Wires :

Testing your Spark plug wires, or testing the resistance in your spark plug wire is a common maintenance item that should be performed when you feel as though your car may have lost power over some time. What you what to determine is whether or not there is a short or break in the wire that may be interrupting your spark energy that is being delivered to your motor.



Step 1 : Take a analog or digital multimeter, and set the unit to it’s setting to measure ohms. Test your setting and your multimeter by pressing the 2 ends ( positive and negative ) together, this should result in a 0 reading on your unit.

Step 2 : As shown in the diagram, put the black (negative) end in one terminal of the spark plug wire, and the red ( positive ) wire in the other end.

Your wire should be reading a resistance, however the style of wire you are using will dictate how much resistance for the length of wire that you are testing. for 8mm Helicore style wires, you are looking at 750-1200 ohms per foot, as opposed to the 8.5 racing wires may register along 40-50 ohms per foot.

Now would also be a good time to check your spark plug wires for signs of burning or arc-through, and take a close look for any cracking or burning on the boots or insulators.

While most performance wire companies, such as MSD or Accel sell helically wound wires around a core or spiral core, solid core wires do not suppress EMI and therefore is not a good solution for most street performance cars.

What Spark Plug Gap should I run?

A : You should always run the manufacturer’s recommendations for plug heat range and gap, failure to follow these guidelines can result in poor gas economy, performance or serious damage to your engine.

How can I adjust my Spark Plug Gap?

A : Once a proper plug is selected, you can experiment with the gap to get the best performance by opening the gap in 0.005″ increments then test to see how much of a gain / loss you have set by changing your spark plug gap.



When should I change my Spark Plug Wires?

A : Spark plug wires are a regular maintenance item, like changing your oil or replacing / rotating your tires. If you have an existing ignition box and the vehicle is a daily driver, replacement isn’t as big of an issue. However if you have a high compression motor with forced induction or running nitrous, you will want to change your plugs and check your wires frequently.

How can I tell when my spark plug gap is wrong?

When the performance of your vehicle falls off, the gap of your spark plug is likely too large and the plug is struggling to create enough of a spark to ignite the air/fuel mixture. Take this time to lessen this gap and restore your vehicle’s power and fuel efficiency.

While Naturally Aspirated vehicles can use larger gaps, turbo or supercharged vehicles will require a smaller gap to prevent spark blowout.