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Selecting The Best Performance Spark Plug Wires

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Can Spark Plug Wires Increase Horsepower?
Cutaway view of a typical spark plug wire

Just like a rotating assembly or suspension system, your ignition system is only as good as its weakest link. Spark plug wires are often overlooked, but they should be considered a wear item and replaced with other secondary ignition parts during a major tune up. Replacing your spark plugs or ignition coil, possibly even your distributor cap and rotor? Go ahead and replace the plug wires as well. While spark plug wires may not “make” horsepower in the traditional sense of adding a performance part to your engine, they can certainly help create the strongest, hottest spark for your combustion chamber, which aids in helping all your other performance engine upgrades like heads, cam, and carburetor to make the most horsepower.

What’s Better, a 7mm or 8mm Spark Plug Wire?

Most factory applications for hot rods and muscle cars were supplied with a 7mm wire, while many newer vehicles were fitted with an 8mm wire from the factory. Today, aftermarket performance spark plug wires are available in 8mm, 8.5mm, 8.8mm, 9mm, and 10.4mm diameters to handle any ignition system you have on your hot rod, muscle car, classic truck, or race car. There has been an argument about 8mm vs 8.5mm plug wires for decades. The diameter isn’t just about looks or having a “fat wire.” No, the diameter increase is due to performance spark plug wires having a thicker spiral core. That thicker wire core provides a lower operating resistance, allowing more spark energy at the spark plug. This thicker core, once wrapped in the insulating material and outer jacket, is what dictates the larger overall spark plug wire diameter. So, theoretically, the 8.5mm will perform better than the 8mm wire, all things being equal.

Lokar Offers Cloth Covered Vintage Look Spark Plug Wires in Six Colors

That said, with today’s electronic ignition systems, be it an external box or an under cap conversion kit, a quality 8mm or better spark plug with RFI suppression is your best solution. If you’re really looking for a classic 7mm look wire for your Flathead or other early engine in your traditional-look hot rod, we suggest looking at Lokar’s trick cloth covered 7.8mm plug wires. They have a cool vintage look and can be configured for standard socket or “HEI” style terminals and look the period part at first glance while only being slightly larger in diameter.

What Are the Best Spark Plug Wires for Performance?
Speedway Motors Offers Several Plug Wires in Kit Form With Stripper, Crimper Tool, and More

Quality performance spark plug wires have two main objectives: simply transmitting the spark energy to the plugs and suppressing the voltage interference. If the plug wire’s resistance is too high, the spark energy to the spark plug will decrease, causing poor performance and potential spark plug fouling. If the resistance is too low it can interfere with other electronics such as fuel injection computers, car audio, or GPS systems, or even cause crossfire issues between the spark plug wires. Crossfire is when the plug wire resistance is too low or the plug wire is compromised, providing a path for the spark energy to jump to an adjacent plug wire, which then fires the wrong spark plug at the wrong time.

The best spark plug wires for the street will use a spiral wound core that is well insulated to protect against RFI (radio frequency interference) while providing a solid fit at the distributor cap and at the spark plug. For racing use with shielded electronics solid core wires may be utilized, but with today’s modern performance spark plug wire construction they are quickly being phased out for spiral core wires with suppression abilities.

A Quality Wire Loom/Retainer Will Go A Long Way In Protecting Your Performance Spark Plug Wire Investment

Using quality spark plug wires that are properly routed and secured by a well-designed spark plug wire loom kit will help you to achieve the best performance out of your ignition system. It is also a good idea to perform routine inspections of your secondary ignition system (spark plug wires, cap and rotor, plugs, and ignition coil) for traces of crossfire, abrasion, wear, heat damage, and more. Quality ignition components work hand in hand to provide the strongest spark to light off your combustion chamber’s air/fuel mixture. Using the correct performance spark plug is just as important as the plug wire connected to it. Visit our Spark Plug Buyer’s Guide here on the Toolbox for a more in-depth look at the world of performance spark plugs and what your engine needs to be at its peak performance, as high-performance spark plugs and wires are the tag team that makes your engine run its best.

Are High Performance Spark Plug Wires Worth It?

A Heli-Core wire (one that uses a spiral wound core and conductive layer) like most aftermarket performance wires will be one of the best upgrades over a factory set of wires. A popular option commonly used on the average street and strip application are the Street-Fire wires from MSD. MSD also offers the 8.5mm Super Conductor Wire, recommended to be used with any ignition control box upgrade. It features a conductor that is helically wound around a special center core that is designed to suppress Electro Magnetic Interference (EMI). The Super Conductor wire will have as low as 40-50 ohms per foot, while a factory set can have up to 1,500 ohms of resistance per foot or more and go considerably higher as they wear/age. Of course, MSD’s wire products are just one of several brands carried by Speedway Motors. Several additional performance spark plug wire options that can be had in universal cut-to-fit or pre-cut ready to install wires include Accel, Moroso, PerTronix, and Taylor. We even offer performance spark plug wire options for the popular GM LS engine family, including direct replacement and swap wire kits.

Are Spark Plug Wires Universal?
This MSD Super Conductor Wire Set is Pre-Made For The 1979-1993 Fox Mustang

The short answer is yes and no. You can purchase pre-cut and terminated wire sets for just about any engine family ever made. These sets are usually determined by the original application, however. A small block Chevy 350 spark plug wire routing in a first generation Camaro versus a small block Chevy 350 in a C10 pickup are going to have different wire lengths, different coil locations, and so forth. These pre-made sets are quick and convenient and are a great solution for these original applications. We carry pre-made wire sets for all the popular muscle cars, trucks, and even many modern muscle cars.

The Two Styles of Distributor Cap Terminals: HEI and Socket
A Universal Spark Plug Wire Kit From PerTronix

Where it can get a little sticky is when you’re dropping that small block Chevy into a 1929 Ford pickup truck with the ignition coil mounted inside the cowl for example. That is when we strongly recommend a universal wire set. The universal wire set comes terminated at the spark plug end and allows you to route the wires as you best see fit, and then terminate the end at the distributor cap for a super clean installation and no extra wire length to deal with. These kits often are supplied with both HEI and socket style terminals and boots, making them truly universal no matter what distributor cap you have, but not all kits do. So be sure of your distributor cap type (see our graphic above) and order your universal wire set accordingly. You can even purchase bulk and individual wires for custom situations where you wish to hide the coil for example. For universal sets you’ll need a quality spark plug wire stripper and crimper to get the job done, but the end results are certainly worth the investment in these tools.

DIY MSD 8.5mm Spark Plug Wires

Updated by Mark Houlahan

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