Iridium spark plug resistance

[gomes512]

I have a '97 Toyota corolla city beater that I've contemplated upgrading with iridium plugs. NGK has the IX line for this vehicle.

On a couple of auto boards I've come across there are posts saying iridium plugs have higher resistance then copper plugs and that this is bad for older ignition systems.

Is there truth to this?

Purely for reduction in maintenance time (only 10mins, but 10mins I can be doing other things). Figure I could possibly change the plugs once for every second set of rotor and cap.

 

[dparm]

What proof do these people have? I have never heard of this anywhere.

 

[gomes512]

Thanks for chiming in.

I was asking myself the same thing. Just wanted to be sure I wasn't overlooking anything (the whole if it ain't broke don't fix it thing). I didn't see anything on NGK's site.

 

[Quest]

Iridium more or less the same as ordinary copper core resistor plugs.


Again: it never seize to amuse me as to where these "info" comes from RE: iridium has higher resistance than copper core, etc.

Q.


Remember 1 thing: regardless of how relatively exotic the materials used in automotive spark plugs these days: your electronic ignition system on your gasoline automotive engine is more than capable of generating high enough voltage to create a spark to jump across the electrode (so as to finish off the job).

 

[mechtech2]

Being copper has no bearing on this at all.
There are no copper tipped plugs, whereas platinum and iridium are the tip material.
Plain steel is great, resistance wise. Platinum actually has more resistance, and iridium is better.
But that is just one part of the whole plug resistance equation.
A total of 3-10k ohms is normal.
Compared to the insane resistance of the gap in a pressurized cylinder, there is almost no relevance.

 

[beast3300]

I don't know about resistance but I thought some Iridium spark plugs claim lower energy to fire. Well anyways, you can put them in your car if you want. It isn't going to hurt it at all.

 

[OldCowboy]

Originally Posted By: mechtech2

A total of 3-10k ohms is normal.
Compared to the insane resistance of the gap in a pressurized cylinder, there is almost no relevance.


+1

 

[Quest]

Originally Posted By: mechtech2
Being copper has no bearing on this at all.
There are no copper tipped plugs, whereas platinum and iridium are the tip material.
Plain steel is great, resistance wise. Platinum actually has more resistance, and iridium is better.
But that is just one part of the whole plug resistance equation.
A total of 3-10k ohms is normal.
Compared to the insane resistance of the gap in a pressurized cylinder, there is almost no relevance.


@mechtech:

"plain steel" is not really plain steel at all: in fact: ordinary copper core plugs, the electrode material is made of nickel alloy for erosion resistance while operating inside a harsh environment (combustion chamber).

Resistance is relatively insignificant in a high KV sparking system, so long as there's enough high voltage on the electrode tip to ionise the air (or inside a combustion chamber: fuel+air mixture) to make the are electrically-conduction (for the spark to conduct from one end of the electrode to the other side), that's all that's required.

Q.

 

[gomes512]

Good info here, thanks for all the replies.

 

[Vikas]

Which resistance? Are we talking about the resistance of the spark plug wire or the spark plug itself?

 

[punisher]

One thing I remember from one of my engine perf classes: The diameter of the electrode is inversely proportional to the voltage needed to initiate the spark. Large diameter copper plugs require marginally less voltage to fire vs narrow electrode iridium/platinum plugs. Voltage requirement differences are due to diameter, not materials.

At least its what I was told.

 

[Errtt]

I've put Iridium plugs in a few motorcycles and on the cold winter mornings, they start easier and run smoother. These bikes do not have a robust ignition system - so seems to me (and I have also heard from other riders), that Iridium plugs are easier on the system.
Before I tried them, a friend was telling me he would typically start his bike, it would die after a second or so, then would have to re-start on the cold morning. Iridium plugs is 1 crank/start now. Also says he gets a little better mileage unlike having new plugs in the past.
Seems to me, easier starts, smoother running - but I can't tell a mileage increase (although I don't generally track mileage well).

 

[Torino]

Resistance of copper plus spark plugs in a pressurized cylinder is in the range of 10's of millions ohms. Who knows exactly how many and it really does'nt matter muck. john--Las Vegas

 

[SteveSRT8]

resistance is EXTREMELY important if you are using the plug to read the combustion chamber events. Mercedes uses this among others.

These systems typically fire the plug and then note the resistance as a measure of combustion, then re-fire as needed.

 

[Bluestream]

Resistance is Futile..

 

[GMBoy]

Originally Posted By: punisher
One thing I remember from one of my engine perf classes: The diameter of the electrode is inversely proportional to the voltage needed to initiate the spark. Large diameter copper plugs require marginally less voltage to fire vs narrow electrode iridium/platinum plugs. Voltage requirement differences are due to diameter, not materials.

At least its what I was told.



I think it may be just the opposite..smaller electrode requiring less voltage.

Atleast that is what the spark plug advertising claims. I've seen Bosch claim it when they first introduced the platinum plugs and now NGK and Autolite claim less voltage needed with their 0.4 and 0.6 sized iridium tips.

 

[mechtech2]

The difference in resistance from any two types spark plugs is NOT what Mercedes is reading. They are reading the insanely high [comparative ]resistance of when firing across a gap in high cylinder pressure.

0-10k ohm from a spark plug either way has no effect.

 

[PandaBear]

Originally Posted By: Torino
Resistance of copper plus spark plugs in a pressurized cylinder is in the range of 10's of millions ohms. Who knows exactly how many and it really does'nt matter muck. john--Las Vegas


If it is 10s of millions of ohms you are talking about the air gap, and right before it fire. During firing the arcing makes it significantly less, and it has nothing to do with resistance of the tip but the air pressure.

Originally Posted By: punisher
One thing I remember from one of my engine perf classes: The diameter of the electrode is inversely proportional to the voltage needed to initiate the spark. Large diameter copper plugs require marginally less voltage to fire vs narrow electrode iridium/platinum plugs. Voltage requirement differences are due to diameter, not materials.

At least its what I was told.


It is the other way around, the narrower the tip, the lower the voltage needed to arc, and the sharper the edge, the more consistent the arc.