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Whether you need an OE replacement set or something purpose-built for extreme performance, thereโs no shortage of pre-made spark plug wire kits available today. But if your project involves a healthy dose of customization โ whether thatโs a power plant living in an engine bay it was never designed for, or significant modification to the engine itself โ you may find yourself in a situation where a custom-made wire set is best option for your application.
Fortunately, universal sets like those offered by Accel and MSD are designed with projects like these in mind, and you donโt have to be a master electrician to make your own wires. Here weโll check out what your options are, walk through the process of building the wires, and get a few tips on how to make sure your new wires are up to snuff.
Universal wires sets, such as these available from MSD and Accel, allow builders to customize the length of each plug wire for optimal fit. Their low-ohm resistance increases performance by allowing more spark energy to the spark plug.
When, Why, And How
With spark plug wires it can be easy to assume that as long as everythingโs plugged in properly, everything will remain copasetic ad infinitum. But as Graham Fordyce of Holley Performance reminds us, a spark plug wire is consumable part, much like a brake pad or a filter. โSpark plug wires are designed to flex, and over time, that flexibility will have an effect on the core. When youโre doing a tune-up, you should always check the resistance of the wires and make sure the wire is not degrading.โ
And that means that even if a spark plug wire looks fine on the outside, itโs not a guarantee that itโs internally sound. โIf it degrades, itโll normally create more resistance,โ Fordyce says. โThat might be tough to detect by the seat-of-the-pants unless itโs at the point where the engine is misfiring, but you are getting less energy to the spark plug. And once it starts to degrade, itโs going to continue to do so.โ
Utilizing the right tools for the job, such as this MSD wire stripper (PN35051) and crimper help make the job of making custom wires go smoothly. They also ensure a rigidly secured connector which will allow for years of trouble-free service.
There are also the demands of high performance builds to consider, he notes. โWhen you build a performance engine, you want as much energy as possible to the plug for a better burn in the cylinder. Any time you start adding things like blowers, turbochargers, nitrous, or you change your camshaft, et cetera, itโs going to demand more of everything else in the motor. And if you canโt burn it properly, itโs kind of a waste to do that.โ
Thatโs where it becomes important to take note of the resistance rating of a given spark plug wire. Itโs ostensibly a balancing act between minimizing RF and electromagnetic interference and delivering the maximum amount of spark energy to the plug. In applications where the latter of the highest importance, a plug wire like the MSD Super Conductor might be just the ticket. With only 40 to 50 ohms of resistance per foot, the loss of spark energy in this wire is minimized, ensuring the cylinder is getting all the juice it needs for a proper burn.
But thereโs also the construction of high performance plug wires to consider, along with the expected use-case. Sets like the Accel 300+ Thundersport wire offer 150 ohms of resistance per foot to better suppress unwanted RFI and EMI interference, an important feature for both street-driven cars and race cars that use data acquisition systems and other sensitive electronics. They also boast thermal protection up to 600 degrees, something that becomes an increasingly important consideration as you ratchet up the performance in your build.
After the wire is stripped, leaving 5/8in of the core exposed, insert the terminal with the core folded back. Crimp the terminal onto the wire and slide it into the spark plug boot. General best practice is to leave a 1/2in or so of slack in the wire length to prevent it from tugging on the distributor.
โAnything you do to make power is going to develop heat, and thatโs going to affect the temperatures under the hood,โ Fordyce points out. โIf you bolt up a turbo in there, for instance, thatโs going to radiate a significant amount of heat on its own.โ
Exhaust modifications are a significant factor as well โ if you change from cast iron manifolds to a set of headers, youโre likely to see increased engine bay temps because the cast iron of the manifold is better suited to retain heat than thin-walled headers are.
Beyond maintenance and performance concern, a new set of properly fitted spark plug wires can provide both aesthetic and pragmatic benefits, too. โA lot of times when you buy a pre-made set, the wires are designed to be routed a very specific way,โ Fordyce says. โSo if you donโt route them exactly that way, your wires are going to be sort of a mess. And if your wire is longer than it needs to be, that extra length of wire is creating more ohms of resistance, thus taking potential energy away from your plug.โ
And custom routing can save time for teams at the track. โA lot of racers like to route them around the valve cover or under the exhaust,โ he explains. โSo if they want to check valve lash between rounds, itโs just one less thing to have to remove.โ
Coil-near-plug engines, such as the ever-popular LS, still require quality spark plug wires. Often, coil relocation or non-factory valve covers require custom wires. MSD offers the correct boots and terminals to build wires for these setups as well.
Get It Together
So weโve established that thereโs no shortage of reasons to get a good plug wire thatโs designed for your specific application. But in situations where a direct-fit set wonโt work, building your own set of wires to the required lengths is the best way to ensure proper fitment, and it allows you to route the wires exactly the way you want to. Fordyce walks us through the process.
โFirst determine what type of boot is going to allow you to route the wire where you want to route it,โ he says. โThat could be under the exhaust, or over it, around the valve cover or over it โ however you want to do it, you just need to determine which boot will allow you to do that.โ
With that squared away, itโs time to figure out the wire lengths you need. โWhat I find to be the easiest way to do that is to install all the wires on all the spark plugs, route them the way you want to up to the distributor, bring the wire up to the terminal end cap that itโs going to connect to, then give yourself about half an inch of extra room for movement, and cut the wire.โ
From there we move on to assembly. โStrip the wire about 5/8ths of an inch, roll the core back over on top of the silicon, and install the terminal. The core goes up against the terminal and you crimp it opposite the side that the core is on, so it sort of presses the core up against the terminal. Then install the boot and youโre done!โ
Strategies For Success
Checking the wires with an ohmmeter ensures they are performing optimally and that an error wasn't made in the assembly process. It's also a great way to determine if your old wires are ready to be replaced.
Fordyce also offers a few tips to make the project as hassle-free as possible. โTry to route the wires away from heat sources whenever possible, and as far away from any electronics as you can. And of course you want to make sure theyโre not near anything thatโs rotating, or any linkage, pulleys โ anything like that.โ
Using dielectric grease is also an option worth considering, though Fordyce offers a word of caution. โItโs designed to help seal the boots to the spark plug or distributor cap, which helps to prevent corrosion and, to some extent, helps to keep the spark from jumping to ground. You have to be careful with it, though โ people seem to have a tendency to use too much, or they donโt apply it correctly and then it gets between the wire terminal and spark plug or distributor cap connections. Thatโs fine if itโs a tight connection, but if the terminal connection isnโt tight, it could insulate the connection over time.โ
And once all the wires are built, itโs important to check your work before they go on the engine. โI typically remove all of them, clean any grease or other debris off of them, and then check the resistance of each of them to make sure there arenโt any issues. If it doesnโt calculate properly, then you know youโve made an error somewhere โ maybe the core slipped when you were crimping and didnโt notice it, or something like that.โ
Checking the wires at this point ensures that youโre not going to be chasing gremlins later on when theyโre on the car, when the origin of a potential issue might be less clear. But if you follow Fordyceโs advice, you should be back to firing on all cylinders in no time. Enter Text Here