308 spark plug wire routing

There are more than a few threads detailing ignition misfire woes and pros/cons of various brands and types of spark plug wires. I’ve read in at least one thread that the stock Cavis wires weren’t great, but my question is more about how to properly route them vs. which type or brand to use.

I’ve read that when routing spark plug wires it’s important to do so in sequence of the firing order to avoid crossfiring, and spacing spark plug wires too close or parallel to each other can also result in crossfiring due to the inductive field which builds up in one wire as the current flows in the other. The wires on my ‘81 GTSi, though, are bundled together as they exit the distributor boots and are not at all separated as they’re held together by brackets and o-rings. It’s almost like Ferrari actually TRIED to keep them bundled together until each plug wire reaches it’s respective cylinder. What am I missing?

Can the factory configuration promote crossfiring, or is routing/bundling not a factor due to the type of wires in this system?





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I can't recall a single report of a functional cross-firing happening. They can "cross-talk" enough that, when using a sensitive timing light, the timing light can wrongly flash at the other cylinder's firing event (so you might need to "unbundle" the spark plug wires some to better isolate the one that the timing light is trying to measure to not get erroneous flashes). Why are you thinking this is a "problem"?

The fine-wire helical construction of the stock wires probably does reduce the magnitude of the cross-talk just from the geometry (compared to straight, parallel solid conductors) and the inductance that it adds (i.e., it reduces the rise time of the spark signal -- which is a good thing anyway to not blow up the output transistors in your Digiplex ECUs).

 

I’m not so much thinking it’s a problem, more like wondering why it isn’t. If I were to replace the wires, what’s the current go-to that would be comparable to OEM, and could I still use OEM routing with these new wires?

 

Haven't bought any spark plug wires lately, but I'd certainly use something with a helically-wound internal construction, and target the stock F resistance of about 700 Ohms/foot. Your bigger problem may be getting an aftermarket wire with a small enough outer diameter to fit the holes in the distributor caps -- IIRC, the stock F wire is 7mm OD; whereas, most of these later super-duper wires are 8mm or 8.5mm OD. Hopefully, someone else can chime in about recent options.

 

1978 GTS.

I just replaced OEM wires with Accel 4040s.

I removed the extenders and replaced plugs (NGK iridium 5s to 6s).

I also rebuilt the carburetors, replaced the Magneti Marelli coil with an MSD High Vibration coil, and I replaced an MSD 6A with a new one.

My car has never ran so well in my three years of ownership..

 

However, you have an aftermaket dist cap (with a different spark plug wire mounting method), and a completely different aftermarket ignition system vs a (Digiplex) 2Vi (although the "spiral construction" description is the proper type so could be OK if the 8mm diameter can fit the stock 2Vi dist cap).

 

Pertronix make 7mm spiral wound plug wires in generic kits with choices of plug end termination

 

Others have used them on various models with success. I was simply sharing my experience, Steve.

 

Too many misfires and and pulsing in the exhaust. My spark plug wires are too old and have multiple opens in the wires, off and on.
So, time to replace them. I purchased Kingsborne spark plug wire with a copper wire core to replace the original noise suppressor type spark plug wires. I very rarely use the radio and cassette player. I prefer to hear the Weber’s since I installed a used airbox without the noise suppression. I purchased the terminals and coil terminal also. I have a spark plug wire “W” crimper to attach them.
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1978 GTS US. Pertronix with Pertronix Coils, 8mm Accel plug wires (had to shave insulation to fit), Low (0) resistance plug extenders from Superfromance (I could get by without the plug extenders but I cut the plug wires to short, my bad). NGK BPR6EIX iridium plugs gapped at 30 thou, rotors with wide contact, no radio noise suppression capacitors either on ignition or fuel pump and of course no timing retard micro switch..
Timing set at 34 degrees total at 5K rpm and about 7 degrees BTC at 1K idle. Fast idle cam set so it won't stall at cold idle.
Hot idle 975 rpm with AC on or 1050 with it off.

Starts and runs great. No crossfire even though I have the plug wires bundled in the stock rubber distributor protectors, no radio noise and no fouled plugs even on long down hill in gear braking (which used to be a problem with stock ignition) or high altitude running.

Barry

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The Pertronix 7mm spiral-wound wires are 500 ohms/foot, Kingsborne 7mm spiral-wound wire is also 500 ohms/foot but I can’t determine if they use that particular wire in their pre-made sets, the Magnecor 7mm spiral-wound wires are 3000 ohms/ft, and the Accel 4040R wires “meet or exceed OE resistance”. It seems like the Pertronix or Kingsborne would be the closest to OEM spec without having a set custom made from that magical last spool of Taylor wire.

 

Summit says the Accel 4040 are also 500 Ohms/ft (which is close enough IMO -- so either the Pertronix or Kingsborne are A-OK):

https://www.summitracing.com/parts/acc-4040?utm_source=bing&utm_medium=cpc&utm_term=+accel++4040&utm_content=Accel&utm_campaign=Part+Number+Ad+Groups

but the 8mm diameter may be an issue -- IIRC, people have reported needing to "trim" the Accel 4040 ends to fit the F dist caps (and I'm not a fan of the non-stock color, but that's just me ).

 

Yup you do need to trim them a bit.
I believe they make them in red so the color shouldn't be a problem.

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