spark plug wire resistance

[marion]

1974 911, 2.7...
the old plug wires measure 1000 ohms,, the new wires measure 4000 ohms.
they look the same, heavy duty with the braided ground wires. Any clue why the old wires are so much different. I suppose they could be the wrong ones?
any ideas?..oh won't the new wires with more resistance lower the voltage to the plug, which may result in a weaker spark?

[Flieger]

According to Ohm's Law, E=IR, More resistance with the same amount of current equals more voltage. Power consumed by a resistor = I^2 x R (Resistance). This turns to heat and saps current.

You will get more voltage with the higher resistance ignition wires but will make more heat and loose some of the current at the spark plug electrodes.

Voltage is more important in creating an arc at the spark plug. You don't need much current to ignite the mixture.

[Zeke]

Originally Posted by Flieger

According to Ohm's Law, E=IR, More resistance with the same amount of current equals more voltage. Power consumed by a resistor = I^2 x R (Resistance). This turns to heat and saps current.

You will get more voltage with the higher resistance ignition wires but will make more heat and loose some of the current at the spark plug electrodes.

Voltage is more improtant in creating an arc at the spark plug. You don't need much current to ignite the mixture.

Best explanation I've read here yet. Maybe others stated the same fact, but not in as clear and simple a way. Thanks.

[marion]

hmm,,, interesting,,,good point, i had forgotten about ohms law,, so if i hear you correctly, the resistance in the wires is higher, so (if the current stays the same) the voltage to the plugs will be higher, creating a better spark?,,i''m a little lost on the power equasion?,, so for the non science readers,,,,what do you think is the "bottom" line if i replace the old 1k ohm wires with the new 4k ohm wires? should i do it?
thank for the lesson...

[Flieger]

Thanks for the compliment, Milt.

I would go with the higher resistance wires. They will give a "hotter" spark and have potential for wider plug gaps. The current loss should not be much of an issue and the higher voltage will be better for getting the arc going.

The very fact that the wires are new makes them preferable to worn out wires.

The main downside of the increased voltage will be faster deterioration of the plug electrode due to the higher "tension" arc. I think the correct, factory-specified Cu plugs in the specified heat range would be fine. Make sure you exercise the car to help fight carbon build-up.

[HawgRyder]

You ppl need to go back to school....LOL
More resistance = less current = less voltage to the other end.
And...the wire will get hotter because you are consuming power in the wire.
Think about the lement in your toaster....it gets hot because it has resistance to the current and voltage running through it.
If you need to drop voltage in the simplest way...you put a resistor in series with the power line.
The best setup as fas as I am concerned is: Zero resistance...high output coil...low resistance plugs....and the correct gap.
The higher the compression...the more volatage and current you need to fire the plug.
Bob
(50 years as an Electronics Tech)

[marion]

Bob,
i do appreciate all the input....
with a good lesson in I, E and R...
.
if i remember correctly, E=I x R,, so if R goes from 1k to 4k, and I stays the same , the E (or the voltage at the plug) would be higher correct?,,, but what is to say that I stays the same? hmm? I need more theory.
.
but i'm getting away from the initial question (what to do), and what practical affect will it have if i change the wires?
.
the issue is the old wires are 1k, the new wires are 4k,,, should i change them?,, .and what impact will that have on how the car runs?,

thanks for the input,,

.

[ossiblue]

Without going into theory, your car originally came with wires and connectors that had a resistance of 4K ohms--1k was in the wire itself, and 3k was in the Beru connector which contained internal resistors. If you were measuring your old wires only, then the 1K resistance is normal. If you measured the new wires with the connectors, you would get the 4K measure.

Regardless, the stock setup was a 4K resistance so using the new wire set is what the factory specified.

BTW, the Beru connector is notorious for "going bad" with breaks in the internals and failure of the resistors inside. This may account for a 1K ohm reading with the connector installed. If your wires were original, it's time to change anyway.

[HawgRyder]

The use of resistance wires was to cut down or eliminate the interference to the radio.
It probably cuts EMP (Electro Motive Pulse)to the electronics in newer cars too.
Personally I do not have a radio in the car....like to listen to the real music coming from the engine...LOL
Depending on the compression of the engine...you may need to go to solid ( or stranded) wire to cut down the resistance and fire the plugs more efficiently.
The newer coils have more voltage coming out of them, so that problem may already be taken care of.
With all the new ignition products around, you have a wide choice (good thing).
Good luck with the choices.
Bob

[911pcars]

Must agree with Bob on this.

More accurately, Ohms Law mainly applies to show the relationship between the three electrical elements, voltage, resistance and current and to calculate an electrical value when two of those are known. However, since the secondary voltage in an ignition system is variable (3000-40,000 volts), depending on load, thus this calculation doesn't apply.

An increase in secondary resistance will require more voltage to fire the spark plug. However, one can accomplish the same effect with a wider spark plug gap. The object is to fire the plug with the least amount of voltage regardless of compression ratio, A/F ratio, spark plug gap, etc. The ignition system already has a hard enough job to do this, much less deal with increased resistance in plug wires. Fortunately, the difference between 1000 and 4000 ohms isn't great enough to make or break the system.

How about introducing another air gap in the plug wires. Would the "increase resistance = voltage increase equation" work then? Uhhh, no. The cylinder would probably misfire. If not, the increased voltage created by the system to overcome the added resistance would stress the system and shorten the service life of rotor, distributor cap, plug wires and coil.

The purpose of resistance-type secondary wires is to suppress radio interference. If 1000 ohm wire does it, so be it. As long as the insulation is intact, the engine doesn't misfire and the radio doesn't buzz, you should be good to go.

Sherwood

[rnln]

Let me take a shot, base on my very basic thought. R increase, I stay the same, E increase. But the E here is not the E at the produce end. Rather it is at the consumption end. Meaning your car will eat more energy somewhere. Hope I am right :lol:
Basically, I would think I want wire with less resistance. Who cares the ohms law. I have not seen it for more than 20 years anyway

Originally Posted by marion

Bob,
i do appreciate all the input....
with a good lesson in I, E and R...
.
if i remember correctly, E=I x R,, so if R goes from 1k to 4k, and I stays the same , the E (or the voltage at the plug) would be higher correct?,,, but what is to say that I stays the same? hmm? I need more theory.
.
but i'm getting away from the initial question (what to do), and what practical affect will it have if i change the wires?
.
the issue is the old wires are 1k, the new wires are 4k,,, should i change them?,, .and what impact will that have on how the car runs?,

thanks for the input,,

.

[marion]

wow,,
thanks everyone for all the input...lots to think about.
.
a follow up for L.J.,
i mesured both sets end-to-end,, very interesting about the 3k in the Beru connector. just wondering what the Beru connector really is, and why the car still runs (if) that portion of the "wire" is bad?
.
OH,,, I reported that the wire were "the-same", that is not 100% correct, the connection into the dist cap is much different. The old 1k wire look like every other plug wire i have seen,,, the new 4k wires are way different, hard to explain, but when you flip it over and pull back the rubber boot, the first impression is 2 pieces of copper on the outside of the center insulation,,very odd for me?
perhaps someone can comment on that design?
.
running the correct plug was brought up several times. I have seen two different plugs identified as replacments: Beru 215/14/3p (or) 215/14/3a.....and Bosch w215T30 or w215P21... can someone explain the difference?,, and which would be better for the old 2.7 with 160K (rebuilt @85K, years ago)... all stock, low compression (8:1), CIS.,, just a nice sunday driver.
,
thanks again everyone...
I had forgotten how effective this forum is...

[ossiblue]

Originally Posted by marion

wow,,
thanks everyone for all the input...lots to think about.
.
a follow up for L.J.,
i mesured both sets end-to-end,, very interesting about the 3k in the Beru connector. just wondering what the Beru connector really is, and why the car still runs (if) that portion of the "wire" is bad?.
OH,,, I reported that the wire were "the-same", that is not 100% correct, the connection into the dist cap is much different. The old 1k wire look like every other plug wire i have seen,,, the new 4k wires are way different, hard to explain, but when you flip it over and pull back the rubber boot, the first impression is 2 pieces of copper on the outside of the center insulation,,very odd for me?
perhaps someone can comment on that design?
.
running the correct plug was brought up several times. I have seen two different plugs identified as replacments: Beru 215/14/3p (or) 215/14/3a.....and Bosch w215T30 or w215P21... can someone explain the difference?,, and which would be better for the old 2.7 with 160K (rebuilt @85K, years ago)... all stock, low compression (8:1), CIS.,, just a nice sunday driver.
,
thanks again everyone...
I had forgotten how effective this forum is...

The Beru connector is the part that actually attaches to the plug. It can go bad in several ways--internally, the connections can deteriorate and the connector loses continuity resulting in no spark. That, of course, would be very noticeable but the problem is, many times the break in continuity cannot be detected with a simple tester unless you actually "tap" the connector to cause vibration.

Sometimes the internal resistors fail and the resistance value will change, that's what I was referring to. The connector will work, but the system is out of balance. As others have mentioned, I don't think the low resistance is a major factor in performance if all else is up to specs.

Bottom line, your new wires will work fine and since you already have them I'd say go ahead and install them.

[Zeke]

Shoot, Flieger's explanation sounded so good.....

So, the question is, if you don't give a hoot about a radio, then are other interferences worth considering? If so, on which models? And are the aftermarket non beru connectors OK? (depending on the answers to questions 1 & 2)

[HawgRyder]

I have cut apart a couple of Beru connectors and found them to be a carbon type resistor encased in the "beru" pkg.
My experience with carbon is that it is very stiff and vibration can cuase it to crack.
If it does crack....the resistance goes up...sometimes hundreds or thousands of time the original value.
If you must use a suppression type wire....there are several types of "spiral" or "magnetic" suppression wires mostly used for racing purposes.
Some of these wires are bigger in diameter than ours, but can be fitted into the cap with small end adapters.
Also available are the aircraft type shielded wires, and some of them are resistance style.
Hope this helps.
Bob

[Flieger]

What would happen if (theoretically) a resistor was inserted into the circuit AFTER the ground electrode but BEFORE the ultimate current dump/ground. Would this raise the potential before the resistor, which in this case would include the spark plug electrodes?

[HawgRyder]

All circuits are really CIRCUITS....
That means that the path from the positive side of the battery MUST eventually get to the negative side.
If you insert a resistance in ANY part of the circuit, you will do several things...reduce current....drop voltage on the high (positive) side of the resistor...and in some cases you will introduce a slight delay in signal (with wire-wound resistors ...because they look like little coils).
And...putting a resistor in the ground circuit can do some nasty things to electronic devices like ignition boxes.
Bob

[marion]

just a follow up..
thanks again to everyone for the answers, thoughts and insights,,
.
checked the resistance on a few more wires and found one that the old simpson 260 won't even read,,,,,very high resistance, as identified in a post above.
.
it appears that the short story here is that the set of wires on the car now are not "resistance" wires. The new set are "resistance" wires (+ 3k ohms). i suspect, like said above, to help eliminate ignition noise in the radio. And as also stated above, a radio can not compare to the most enjoyable growl of the 911.
.
i do intend on replacing the wires, rotor, cap and plugs at the first opportunity.
can't wait for the increased performace.
.
thanks again,
marion..

[Flieger]

I have been thinking and reading more about the electro-dynamics of the ignition system. Skin effect, resitance, inductance, capacitance, etc. Also, I see that the super high voltage current in the CDI system behaves much like Alternating Current in that the energy is transmitted through the magnetic field surrounding the moving charge (skin effect). This makes measuring wire resistance more complex because the coating of the conductor is the more important material at high voltage but this is bypassed at low voltages used with ohm-meters.

I now think that (if radio interference is not a concern) low resistance ignition wires would be the ideal set-up.

I still am sticking to most of my earlier assertion about Ohm's Law and increased voltage due to higher resistance. However, I now am revising my conditions.

If there were an increase in the resistance across the spark plug electrodes, this would cause a higher potential/voltage. The key is to have all of the resistance of the ignition circuit contained in the electrode gap so that all of the voltage drop (total voltage drop for the circuit staying constant) takes place in the arc of the spark plug. This way the arc is at maximum power and voltage. It can then fire across a larger gap and fire a higher octane, compressed air/fuel mixture.

[marion]

i checked with the resident GURU this am,, and your last thoughts are similiar to his.,,,,,
.
the ignition system must be viewed as AC not DC, which complicates the math.
.
so would that imply an impedance calculation (inductance and capacitance)?,,,
wow, interesting where the discussion lead,,,, and all i was interested in was what affect (if any) that "resistor" wires might have,