About Ignition Wires
Comments on Wire Types
Spark Plugs


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The spark plug wires conduct high voltage current from the distributor or ignition coil pack (distributorless ignition systems) to fire the spark plugs. The spark plug wire's job is to provide a conductive path that doesn't leak voltage. The earliest spark plug wires were copper, aluminum or steel wire wrapped with insulation sufficient to contain 12,000 volts. But when high voltage current surges through a low resistance wire, the wire becomes a broadcast antenna and sends out radio waves. This causes radio frequency interference (RFI) which disrupts radio and television reception. In vehicles built during the past 20 years, RFI can also play havoc with the car's computer, ignition and fuel injection modules. So the plug wires must also "suppress" the troublesome RFI. This is done by using "resistor" wires that create enough resistance to suppress RFI, but not so much to interfere with proper ignition.

Resistance in the spark plug cables can be created one of two ways:

  • by using graphite-impregnated fiberglass strands (commonly called "carbon-core" wires) to carry the high voltage current
  • or by using a special nickel alloy resistance wire called "spiral" wiring.
The spiral wire is wound spring-like through the core of the cable. The spiral wound wire reduces RFI with less resistance and better conductivity than standard carbon-core cables.

Spiral cables are considered to be "premium" grade wiring. Because the wiring has less resistance than carbon-core cables, the voltage required to fire the plugs is lessened, which aids starting and reduces the odds of misfire. And unlike carbon-core ignition cables, spirals won't deteriorate over time.

Carbon-core cables have little particles of carbon impregnated in strands of fiberglass. Over time, the carbon particles tend to bunch up and separate. Heat and vibration contribute to the aging process, as does twisting or jerking on the cables themselves. Once the carbon begins to separate, resistance shoots up. This raises the voltage needed to pull current through the wires and fire the plugs. If the ignition system can't overcome the resistance, the plug misfires. At this point, the plug wire needs to be replaced.

A bad plug wire with excessive resistance usually causes an intermittent misfire rather than a steady miss. This happens because the voltage required to fire the plugs changes with engine speed and load. It is lowest at idle and under light load, but rises sharply as the throttle opens or the load increases. Thus, the engine may run fine most of the time, but then misfire or stumble during acceleration. Unless the cables are replaced, the carbon-core will continue to deteriorate. The symptoms will worsen and eventually the occasional misfire will become a constant misfire.

When Do They Need To Be Changed?

Original equipment plug wires are supposedly engineered to last 100,000 miles or more. But in real life, they seldom make it. Heat, vibration and mishandling can drastically shorten the life of the wires. After 50,000 miles or more, the insulation may begin to break down and internal resistance may be inching up.

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Some wires fail from the inside, due to a breakdown of their insulation materials. Wires should always be inspected and tested whenever a rough or erratic idle is present, poor acceleration is noticed, a decrease in fuel mileage is experienced or a vehicle fails an emissions test due to high hydrocarbon emissions or cylinder misfire fault code.

"What are some common problems that prevent spark plug wires from working properly?"

Excessive heat from exhaust headers- Routing spark plug wires in areas with excessive heat can destroy the silicone insulation. To prevent this, all Bosch spark plug wire sets are designed specifically for each application to ensure wires are out of harms way.

Some experts suggest replacing 7mm carbon-core ignition cables every 30,000 miles as preventative, while others say 50,000 miles is more realistic for today's cars. In any event, the cables eventually have to be replaced -- but most people wait until they start to experience a misfire before doing anything about it.


A professional mechanic can spot a bad plug wire with too much resistance by watching for an unusually high firing voltage on his scope. Resistance can also be checked with an ordinary ohmmeter:

  • For cables less than 25 inches in length, resistance generally should not exceed 30,000 ohms.

  • For those over 25 inches in length, the maximum acceptable reading is 50,000 ohms.

If an ignition cable is chaffed, has age cracks, or burned spots in the insulation, or is arcing (shorting out), the wire needs to be replaced.

An easy way to check for arcing is to wait until dark, then start the engine and open the hood. CAUTION: Keep your fingers well away from the plug wires and moving parts under the hood! If you see any sparks in the vicinity of the plug wires or plugs, or hear a "snapping" sound, it means the plug wires are arcing and need to be replaced.

Silicone insulation is superior to Hypalon insulation in terms of heat resistance and longevity. A Hypalon cable touching against a hot exhaust manifold will likely melt through while a silicone cable usually will not. The thickness of the insulation is also important. The thicker the cable, the more voltage it can handle. That's why many late-model high-voltage electronic ignition systems have gone to 8mm, rather than 7mm silicone ignition cables. Silicone costs more, but performance-wise it's worth it.

MSD Spark Plug Wires:
The MSD Heli-Core Ignition Wires are perfect for passenger cars, tow vehicles and performance cars. The wires are 8mm and can be relied on to deliver all the high voltage your engine needs! Heli-Core wires feature a stainless steel conductor that is wound around a special glass core. The stainless conductor provides a low resistance path for high voltage to flow while keeping Electro Magnetic Interference (EMI) to a minimum. By winding the conductor around a special glass inner core, the EMI is suppressed inside the wire where it cannot interfere with other electronic devices on your vehicle.

Heli-Core Wires also prevent a phenomenon known as Inductive crossfire. When two wires are routed close to each other and happen to follow the firing order of the engine, the spark from one wire could be induced into the other wire. This would cause the other cylinder to ignite far advanced and will cause detonation. For example, the firing order of a small block Chevrolet is 1-8-4-3-6-5-7-2. Notice that cylinders 5 and 7 are next to each in both the firing order and the in their position in the block. If the spark from the number 5 plug wire is induced into the number 7 wire, a spark will occur in the cylinder causing detonation. Sooner or later engine damage will occur.

MSD Spark Plug Wires prevent inductive crossfire with our special winding procedure and center core material. The EMI and voltage is held within the wire and is transferred only to the plug!

The MSD Heli-Core Plug Wire is available in Universal Kits and Bulk Lengths.

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Spark plug wires are very important to the operation of your ignition system. A good quality, helically wound wire and proper routing are required to get the best performance from your ignition, such as the MSD Heli-Core or 8.5mm Super Conductor Wire. Helically wound wires provide a good path for the spark to follow while keeping Electro Magnetic Interference (EMI) to a minimum. Excessive EMI, such as the amount that solid core wires produce, will interfere with the operation of the MSD. Solid Core spark plug wires cannot be used with an MSD Ignition.

121-3119-9 V8 HEI & Non-HEI, Multi-Angle $75.99
PN 31179 - 6 cyl for me with Superconductor 8.5mm metal core
PN 31199 - 8 cyl version with HEI and straight plug boots



[MSD Super Conductor Ignition Cables]
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After installing an MSD SCI high-energy ignition system on our 1998 Honda Civic EX, we decided the next logical step in the upgrade was a set of high-performance spark plug wires and some new spark plugs. A commonly known electrical law is that electricity will travel the path of least resistance. Usually, this is the spark plug.

But an MSD Ignition Coil applies a 65,000 volt potential, and if you have a high-strung engine the spark plug may no longer be the path of least resistance. Those of you with a high-RPM misfire know this well, as the spark plug energy will fire between the engine block and spark plug wire instead of inside the combustion chamber. MSD Super Conductor wires keep this 65,000 volt potential under control by using a tightly-wound conductor. Winding the conductor prevents electricity from jumping off the wire, and MSD has managed to wind 40 feet of copper wire into every foot of their Super Conductor wires!
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[Forum on spark plug wires ]

I recently bought wires from Autozone they are the ones that are double silicone. and i dont like them. the boots on the cap don't seem to stay on all the way.. like the connector goes on but the boot doesn't stay on.... what are the best for a 93 4.3? i was thinking maybe i should just get some delcos....


I like my Taylor 8mm race wires. Fit nice no problems. Since I need 135 angle boots.

Since the inception of the newer versions of HEI, the stock wires, dollar for dollar, are the best. They match the resistance requirements of the distributorless ignition system.

The new MSD Super Conductor Wires are 40 ohms per foot compared to stock wires at1.2k-1.5k ohms per foot.

I like my Crane 8.5's.

Wholeheartedly agree the MSD wires are super! A close second are some of the Jacobs wires. The ohms per foot of the MSD is superior, and I get to watch the spark lines on the scope while doing a dyno run on chassis dyno, you can SEE the differences in the extra hash, and spark scatter among the lesser brands, then see the crisp clear spark line of the MSD wires under full load, wide open throttle power runs. I have even noticed a drop in hydrocarbons = (un-burned fuel), going from OEM to the MSD wires with no other changes made.


Hey Speedy have you tried any of nology's parts or know someone who has? bg Yes we did it at Autozone for a demo. All the wires were from 40 ohms per foot to just a tad over 150 ohms a foot, except the Accels, they were over 320 ohms per foot. Wires included where MSD, Crane Firewires, Accel supers, stock A/C Delco. The stock ignition systems used on the 96 and up motors has a 100,000 mile recommended tune up point, why: they're that good.

Nothing approached 1200+ ohm's per foot. Older wires, pre-1990-ish , yes, they do approach that number and also the older aftermarkets did too. Not today, not anymore. I did run a set of MSD after I installed the JBA's, fried them to a crisp and am are currently running stock ones again that have 60,000 on them for the wires that melted. Its your money...

If it fires, it fires, no special plug or wire makes it better under 5000 rpm's, this has been proven countless times.

Nology Hotwires.

I've never tested them but I'd like to. They have capacitors built into the wires so they store current and then discharge it very quickly (short duration). This method would only work in certain applications, so most serious racers don't use them, they go with the MSD or Electromotive style of 20* to 60* spark duration. Plus, any serious amount of current through the Nology's would fry them. That's why they work best with older style stock ignitions.

I've done a few tests on other plug wires (AC-Delco, Packard, MSD, and the Duralast double-silicone from Autozone).

The AC's & Packards were complete garbage and the Duralast's from Autozone showed gains in power and mileage over either. This test was done in 1993, and the Delco's are probably better now.

I then tested the Duralasts against the MSD's. The MSD's were a little lower in resistance than the Autozone wires, but none of my tests showed any gains by using them.

The difference in resistance was insignificant compared to the resistance of the plug gaps, and the build quality was very similar. The Duralasts were lifetime wires so that's what I run on everything now including my ten-second camaro. I really like MSD products, but Autozone is just more convenient and gets the job done.
white2001 wrote: Speedy 87ss, are those NAPA wires solid cores with zero resistance?

The napa wires come in different stages: I, II, and III. The stage III are the solid core race only,, the stage II are good low resistance street wires for ecm equipped vehicles, and if they even still make the stage I, I think they are more for the dressup crowd, and not really a performance wire.


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Date: Mon, 19 May 1997 06:37:55 -0700From: "Mackiewicz, John J" Subject: MSD Super Conductor Wires / IdeaTo: "''"

All, I just installed a set of MSD Super Conductors on my '83 22R and noticed a definite improvement over the stock & Autolite wires. Idles a bit smoother, revs a bit easier, and seems to have a little more grunt in 5th gear. I bought these wires from Summit Racing, a universal 4cyl set for $64.



[Platinum Plugs General Info : ]

Longevity is the driving force behind the current rash of platinum plugs. I remember back when Bosch platinums were supposed to be the trick plug to run in your car. After a while I found they worked really well with the low voltage systems used by the British and Italians, and poorly with others (such as GM's HEI system).

All claims of superior performance to the contrary, platinum plugs are not performance oriented plugs. In fact, platinum is not even a very good material to use as an electrode. If you push the plug makers (or if you get to talk to their tech people instead of sales/advertising) they will admit that for a performance plug, you want something other than platinum. But for engines where access is bad, you really do want to use a plug that will need changing as seldom as possible (I see a bunch of300ZXTT owners nodding their heads!). Another factor in the development and marketing of platinum plugs is that the car makers wanted to brag about how many miles their cars would go between tune-ups and so pushed for long life plugs