Spark plug wires - allowable resistance

y_p_w > wrote:
}
}> If one wire is 2' long and measures 'say' 100 ohms, then a 1' one should
}> measure 50 ohms and a 3' one 150. The readings should be a mathematical
}> increase or decrease in proportion to the length.
}
} Those numbers would be WAY too low. I measured the DC resistance of
} some old cables, and it was in the 5,000-10,000 ohm range.


There are different construction techniques for ignition wires. Most
wires (factory and cheap replacements) are resistive. These are
10kohm/foot or therabouts. The good wires are lossy inductors (a fine
wire wrapped around a core) and only measure 100 ohms/foot or something
close. You can get a lot hotter spark with these. In an old car that
burned oil good wires cured my spark plug fouling problems.

--

Frank Ball

On Tue, 23 Nov 2004 08:14:57 GMT, y_p_w > wrote:

>
>
>TE Cheah wrote:
>
>> | unless the engineer has a massive data base to check he can't know.
>>
>> 1 thing is obvious, u don't have ½ a diploma in elec engneering
>
>I have a degree in electrical engineering. Off the top of my head,
>I have absolutely no idea what the allowable resistance for plug
>wires is. As with many things done by engineers, one looks things
>up. I've got various specs, books, and documents sitting on my desk
>at work. I can assure you that I don't have everything memorized
>in my head. I could ask my coworkers, and I'm guessing they don't
>know either.
>
> From a purely electrical standpoint without EMI to worry about,
>stranded high-conductivity oxygen free copper would probably be
>ideal; the stuff would be cheaper than resistive plug wires. Real
>world considerations dictate that wires must be made with other
>materials/designs such that they don't screw up your radio and/
>or engine computer. Resistance isn't that big an issue. The
>biggest problem would be if in the insulation breaks down and
>there's arcing between the wire and the valve cover/engine block.

What he said. I've always used the spray bottle test where you spray
water mist on the wires in the dark and look for arcing. IMHO, over
time and heat the wires cook and develop cracks that allow
leakage/arcing especially in damp weather. Don't know how scientific
it is but it works as a diagnostic tool.




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