waveoff

iTrader: (11)

I'm starting this stupid thread because I can't find a straight answer after endless searching. I just changed the mother f'ing plugs the other day and figured I would test the resistance of the plug wires for the hell of it. Wires 6 and 8 were a bit corroded and showed 7 KΩ and 13 KΩ respectively. All of the other wires were in the 360 Ω range. I figured it was time for some new wires since these have over 100,000 miles on them. I researched different brands of wires on here to see what people had to say about them. Most numbers people quoted were from advertising or manufacturer claims. In my quest for plug wires I went to the various chain stores to see what they had to offer. I was suprised to learn that my old, tired wires were actually decent!

I'd like this thread to be a reference to all with concrete information from actual tests. Please post the brand of wire and it's resistance (average of all 8 wires) as a bare minimum. Add any other pertinent information that may be useful...e.g. wire construction/specs, price paid, where you bought them, etc.

Here's what I've discovered so far...

Stock GM w/100k miles... 360 Ω
Autolite Professional Series (Advance Auto Parts brand, $35)... 900 Ω
Duralast (AutoZone brand, $34)... 1000 Ω
MSD 8.5 mm w/0 miles (P/N 32819, $62 off of eBay)... 25.2-26.4 Ω

I ended up ordering some MSD's because I tested an MSD wire that was twice as long as an LS1 wire and it showed 130 Ω. For $62 shipped I figured, "what the hell."

cantdrv65

iTrader: (3)

I have the MSDs, I've never checked the resistance but they are very durable and easy to shape so they dont lay on the header tubes... Ive "heard" they offer the least resistence to current flow as well...

waveoff

iTrader: (11)

As soon as mine are delivered I'll test the resistance and post it up. I'm glad to hear they're durable and offer good fitment.

P Mack

iTrader: (6)

If I remember right all my msd's were between 35-50 ohms. The difference between 300 ohm and 30 ohm spark plug wires probably makes an insignificant difference in power.

Adrenaline_Z

I wouldn't be too concerned about wire resistance considering the average
resistor type spark plug is ~ 5000 Ohms (plus a 0.040 - 0.050" air gap).

Resistance in the wires is used to supress interfernce from the voltage (EMI)
which can screw with sensor/PCM signals and radio reception, etc.

joecar

GM stock w/35K miles on the wires, average 357Ω
Taylor Spiro Pro 8.5 mm w/30K miles on the wires, something like 60Ω (I'll go measure it again).

joecar

That's true, but a sprial-wound low-resistance wire concentrates magnetic field lines ('flux') very tightly inside the conductor or very close to its outside surface, so it has much smaller electromagnetic losses (less EMI given off) compared to a non-spiral-wound resistance wire which places all the mag field lines all around the outside of the conductor (lots of EMI)

the resistance flattens out the tip of the spike when the plug fires, reducing high frequency emissions (these would interefere with PCM frequencies).

using an inductive pickup, I pick up a good signal from stock wires, but I have trouble picking up a signal from spiral wound wires.

1989GTA

Granatelli and 1 ohm. Thats right 1 ohm.

Adrenaline_Z

Not entirely. Resistance alone is not flattening the spike you see. It is a combination
of resistance, inductance and capacitance that is altering the voltage peak.

The strobe from your timing light uses these spike to time/trigger the strobe.
If the pulses are dampened that much, you can get a more sensitive pickup,
or timing light to measure spark lead.

joecar

You're correct, mostly inductance and some capacitance are also involved.

Actually, it's an expensive inductive pickup I use on my cheap scope meter;
with stock resistance wires: it picks up big voltage spikes (matching RPM/2);
with spiral wound low-resistance wires: it has trouble picking up any signal.

BAD ASS TA WS6

iTrader: (5)

Eh, every MSD I've ever tested has been all over the board. Good wires but I don't like how sporadic they've been.

I run Taylor Thundervolts in my car, and like them. I'll definately be buying another set. Some people have complained of the boots pulling off. But if you pull a spark plug wire off correctly, they are hardly ever any issues, with any wire.

These ohmed out at 30Ohms.

DavidNJ

So is the resistance at 9 volts steady state the same as 40kvolts rising and falling in a few milliseconds?

Adrenaline_Z

If this was a closed circuit, the DC resistance of the wire would not change
(assuming temperature, gauge capacity, etc. was sufficient/constant).

Since there is a rising and falling voltage field with an open end (spark plug
gap) the wire acts as a capacitor storing some residual charge.

If the pressure in the cylinder never changed, and the power required to
ignite the mixture was always the same, you could say the 'impedence' of the wire never changes.

In reality, the amount of charge left in the wire will vary. The more charge
remaining requires less voltage from the coil to jump the spark plug gap.

This would effectively lower the dynamic electrical resistance (impedence)
of electron flow (this is also known as reactance - Google it!).

It's sort of like comparing pressure differentials in the intake manifold against
pressure in the cylinder. If the pressure waves are flowing in the correct
direction and timed well with the valve events, you'll end up with more charge
in the cylinder with less effort needed by the sweeping piston.

joecar

That's correct, the resistance of the wire does not vary (except with temperature change).
The reactance of the wire varies with the pulse width [or it's inverse] (in case of a pulse) or with AC frequency [or it's inverse] (in case of steady state AC).
The impedance of the wire is the sum of resistance and complex reactance.

cantdrv65

iTrader: (3)

Testing the resistence of a wire with a VOM is not an accurate way to test if the wire is actually good however....A wire could easily show good on a VOM yet still be bad under load. A VOM does not apply a load to the wire.....Hence no real current flow.

joecar

Very good point , and a VOM/DMM/Ohm-meter measures only resistance and not reactance ,and can't measure if the insulation is bad/broken.

(BTW: when measuring wire resistance, the wire should be flexed and rolled back and forth, since this will/may show any 'intermittent' type of breaks in the core.)

joecar

So the question is, what are people's measured resistances on their new and/or used wires, and why would you want high or low resistance.

waveoff

iTrader: (11)

LOL, you guys are giving me a headache with all of this technical chatter! I guess this IS Advanced Performance Tech though. Good info...

I'm just replacing my wires because the contacts on two of them were corroded. The junkyard won't sell me just two wires...and they want too much for 8 used ones.

joecar

Sorry, didn't mean to give you a headache

waveoff

iTrader: (11)

No biggie...I actually like reading technical stuff like this to better understand things.