Scott Parker
August 28, 2013

On the surface, spark plug wires are a pretty basic part – they carry spark energy from the distributor (or coil) to the spark plugs. But when you actually go to purchase a set, you find out that there are a million different kinds with many different features. It can be difficult to figure out what is best for your application. Thankfully we stumbled upon this helpful blog on Accel’s website that helps make things easier. The fact that Accel carries 8 different kinds of plug wires highlights the issue. Rather than reiterate the info in Accel’s blog, I’m going to give you an even simpler take on how to chose the best spark plug wire. First you need to figure out what the application is and work from there.

If you own a late model with a few bolt-ons or a 2,500hp drag car with a custom turbo kit, your needs could be drastically different. Late model vehicles tend to have many electronic devices such as satellite radios and GPS navigation, which means that a plug wire with the highest level of EMI (electromagnetic interference) and RFI (radio-frequency interference) suppression is ideal. A race car with lots of fancy datalogging equipment may also require this as well. Typically manufacturers use some sort of wire wrapped around the core of the plug wire to suppress this electric noise. On Accel’s 4000, 5000, and 8800 Series a carbon graphite suppression material surrounds the fiberglass and Kevlar stranded inner core. This is material similar to many new OEM wires, which usually boast very low RFI. However, the 7000 all the way up to the 9000 Series use a Ferrite element for the highest suppression possible.

You may be wondering why all wires don’t come with maximum EMI and RFI suppression. The answer is cost and resistance. Resistance is the biggest buzzword when it comes to spark plug wires, but it usually comes at the cost of EMI and RFI suppression. And despite all the hoopla surrounding resistance, it will not typically make any difference in horsepower in an otherwise healthy and properly functioning motor. Even less so on today’s high-output, distributor-less ignition systems. It also important to note that all things being equal, a low resistance wire can’t hurt the performance or durability of your engine, but too high a resistance can cause a weak spark and potentially rob you of power. With an all-out race car or something with a points or magneto ignition, a low resistance wire may be the way to go in order to maximize the available spark energy.

Heat resistance and durability is yet another concern when it comes to plug wires. In extreme applications, like a 2,500hp twin-turbo crammed into a Corvette or Viper, the wires will actually melt. This is exactly why Accel makes the 9000 Series, which withstands 600-degrees on the wire itself and 2,000-degrees on the ceramic covered boot. However, the Pro 25 and 300+ (7000 Series) offer just as much protection minus the boot. The colored silicone jacket is what provides this heat resistance, though it can also increase the wire’s electrical resistance (the same converse relationship seen with EMI/RFI suppression). If you’ve ever changed the plug wires on your daily driver, then you’d know that cracking and separation is very common – especially around the boot. A higher quality wire will stand up better to the many heat cycles that a daily driver endures as well as the extreme temperatures that our modified vehicles and race cars see as the result of exhaust arrangement, turbochargers and other power adders, extended periods of high RPM, etc. However, you will still need to change plug wires nearly as frequently as spark plugs to ensure a healthy engine.

Size is perhaps the last thing to consider when it comes to spark plug wires. Most manufacturers recommend an 8 or 8.5mm plug wire on most applications. Exceptions would be an all-out race car or a street rod where EMI/RFI suppression is not a concern, but weight and appearance are. In which case, a 5 or 7mm wire might be a better option. Of course on these types of builds, remember to go with a universal DIY type of wire, which is cut-to-fit. By building your own plug wires you can elect how you would like to route the wires, just make sure they come with the right shaped boot.