Copper v. Platinum v. Iridium

I wanted to get a sound-off on plugs. I'm about to replace mine and I'm weighing the pros and cons of each. But nothing can compare to real-world experience. Particularly if someone has used different metals in the same bike and can directly compare and contrast.

Copper: cheaper, best conduction, highest thermal conductivity, gaps are spec'd assuming copper, shortest life.

Platinum: mid-price, least conductive, lowest thermal conductivity, much greater life than copper.

Iridium: most expensive, mid-conduction, mid-thermal conductivity (but closer to Platinum than copper), greater life than platinum.

As an electrical engineer, I might be over-thinking this, but, spark energy and exact timing is directly related to the gap between terminals and the gas makeup in that gap as well as the "source impedance" of the terminals supplying the spark.

A larger gap means more voltage has to build up before an arc can occur. So a larger gap will result in a longer time or delay until the spark occurs (we're talking hundreds of microseconds here, maybe single-digit milliseconds). (Side note, for reference: at 2000rpm a plug fires every 30ms, at 8000rpm it fires every 7.5ms). A larger gap will also mean more energy in the spark.

A more conductive (less resistive) metal will result in more of the energy transferring to the spark, and less being lost in the resistance of the conductor. But, seriously, this has GOT to be negligible. Copper is about 50 times as conductive as platinum, which are the two extremes in conductivity. So that would mean that Platinum loses 50x as much energy to resistive losses than copper. However, one must also think about the percentage of total energy that is going into the spark vs into resistive losses. I would wager that it loses much less than 1% of the total energy in the resistive losses. Thus making conductivity not worth discussing [other than to make this point, right? ]

I originally thought that electrical conductivity might affect the voltage at which an arc would occur, thus affecting its timing and energy level. However, my second-thought on this is based on the fact that arcing is dependent on only a few things: the conductivity and dielectric strength of the material being arced through, and the surface area of the terminals. (Smaller terminals will arc at lower voltages (earlier) than larger terminals.)

So on that thought, I've heard that there are differences in surface area between the different plug types. This could affect arcing voltage and would have to be compensated for by changing the gap.

Thermal conductivity plays a role in pre-ignition. A plug that conducts heat away more poorly is more likely to get hot enough to ignite the compressed gasses early. This, of course, could be combated with high-octane fuels, IF it's even a problem. The worst thermally-conductive material might still never get that hot.

Let me sum up my theories.

Despite people claiming that you should stick to copper because of its superior electrical conductivity, the improvement is likely (without an actual analysis) moot. So don't look at conductivity at all when comparing.

Thermal conductivity could potentially play a role, and an analysis or simply a real-world experience could answer this question. Not to mention, if the worst thermally conductive material did cause pre-ignition, it could potentially be avoided with higher octane levels. This is where I want the most sounding-off.

If there is indeed a difference in surface area of electrodes between the different plug materials, this would need to be compensated for by changing the gap to achieve the same voltage of arc. But I'm not sure the surface area claims I've heard are true.

So if all other things being equal, longest life should prevail.

/rant

Anyone have problems with detonation (pre-ignition, knock, ping) using Platinum or Iridium that doesn't happen when you use copper?

Anyone know if there are surface area differences between plug types?

Any anecdotes on performance, sound, feel, or other noticeable differences when you used two or more different plug metals?

Sorry for the long post. I'm verbose and thorough and often write through stream-of-consciousness.

And now, some data (source:wikipedia):

||Metal|| ||Melting Point|| ||Electrical Conductivity|| ||Thermal Conductivity||
||Copper|| ||1085 C|| ||59.6 x 10^6 S/m|| ||401 W/(m K)||
||Platinum|| ||1768 C|| ||9.52 x 10^6 S/m|| ||72 W/(m K)||
||Iridium|| ||2466 C|| ||21.23 x 10^6 S/m|| ||147 W/(m K)||

 

Copper ?? They use a copper CORE to help conduct heat, but it's inside IRON, or steel. It will rust, not turn green.

Electricity jumps something like 27% easier from sharp edges, which new plugs have, and what the THIN Platinum electrode similates. And I don't think they run the "less conductive" Platinum thru the whole plug - - just the tip, it's too expensive.

There's also an air-gap INSIDE spark plugs, which helps them fire.

I file my plugs square, then gap to 0.027" , just inside spec, as XJ's have weak coils.

An increased gap WILL retard timing, I don't know by how much.

 

Right. But these are the terms used to differentiate plugs and these metals are their primary makeup. And copper on the outside would just sputter away, anyway with all that arcing. I do realize it is not 100% copper/platinum/iridium. But these are the primary conduction paths and these are the materials that typically make up the bulk.

And now that I think even more about it, the iron or steel in copper is a pretty poor conductor (relatively), but there is so little of it that the copper still dominates.

The spark gap inside the plug helps with dV/dt at the terminal. Arcing is actually a function of MANY things. Gas composition, pressure, electrode shape, dV/dt (how fast the voltage rises). I used to build large spark gaps for R&D projects. I could almost write a dissertation. (If I haven't already here).

Point is, these materials could affect spark energy and timing and I want to know if anyone has seen any real differences.

If anyone using platinum or iridium gapped within spec' and had no appreciable degradation of performance from knocking, retarded timing, overheated plugs, etc, then I'm going to go with iridium, because, at that point, longevity is the only determining factor, and despite the cost difference being huge as a percentage, it is not huge in dollars.

If anyone knows of some industry research (by independent labs, schools or an engine manufacturer not paid off by the plug industry) that looks into these differences, I would love to see it!!!

 

Long story short: The local roadrace team uses iridium plugs and opens the gap up somewhat from standard. Modern bikes have plenty of ignition umph for this and they actually can see a very slight power increase in some cases.

Another long story short: We're running Denso Iridiums in both of our Turbo Secas and they actually made a difference, believe it or not.

 

Does an 82 XJ650J Maxim count as a "modern bike with the umph?"

I was planning on buying an entire backup set, gapping to minimum, riding, gapping to nominal, riding, gapping to maximum, riding, and seeing if I could even tell a difference. If not, I'd keep those plugs in. If they were so bad they weren't drivable, just swap 'em out.

 

A couple years ago I replaced the "regular" copper plugs with Iridium plugs in my 97 XJR, hoping to see some performance improvements however the car developed a rough, lumpy idle. I put copper plugs back in, problem solved.

My Subaru H6 gets Iridium plugs, they are a challenge to change and the iridium plugs do last longer, which probably contributed to their development. Seems like manufacturers are striving for "maintenace free" for the life of a lease period.

I run regular plugs in everything old as I'm not sold on any performance improvements using iridium.



Dave

 

I just modified my timing plate to advance the timing 3 deg, what kind of plug/gap would it take to equal something like that. I think gap vs timing are insignificant.
A more efficient coil might be a better place to look for improvements

 

I wouldn't know where to begin on changing gap to effect timing changes. I only know that it will affect the timing. I also want to keep this on topic. Let's discuss the advantages/disadvantages of the various metals for spark plugs.

Also, a "more efficient" coil is a loose definition. Efficient in what manner? And more efficient doesn't necessarily mean performance gains. If you change the coil you will change inductance, capacitance, resistance and this over all output impedance. This could result in more or less total energy being transferred to the spark. It could also change the time at which the energy transfer occurs (changing your timing) as well as the duration of the energy "pulse" (thus changing the power of the spark).

Changing a component like that, however, is likely to have minimal effect because there are so many more dominant factors in play. In fact, this is one of the reasons they put air gaps inside spark plugs. Otherwise, just changing wires would have a huge impact.

Think of it like your carbs. You change a seemingly tiny setting a top-performing bike becomes a non-starter. That's really sensitive to change. Depending on what coil you put in the mix, you could unbalance things in a way where they don't work, even if the coil is "better, faster, more powerful and more efficient."

But, yeah, let's get back on topic.

Advantages/disadvantages of various plug metals? the kind of reply Super posted is exactly what I'm looking for. I'm leaning towards copper because that was what the engine was designed for and what they used to spec the gap setting. Copper is also cheapest and better with heat. I don't mind changing them out too often. (Then again, I haven't done it yet, could be difficult on this bike...)

 

Everything new and old that we put iridiums in has run fine (sparkplug-wise anyway ). And I'm talking about bikes from the 60s through present day. They just seem to make the most out of whatever energy is available.

Barely Legal Bikes
Athens, AL
256-232-2160

 

A fellow Alabamian. I've transplanted to Ohio two years ago. Miss my home. These folks don't know food, and they keep bragging about this stuff they call "chili" from Cincinnati.


Anyway, fan or not I don't get enough of this anymore, so War Eagle.

And thanks for your input. No loss in performance, any gains?

 

before you start testing plugs, read this
http://www.fordmuscle.com/archives/2000/07/indexplugs/
it could be the difference between starting and not starting
a more efficient coil is one designed in this century

 

If you have a High Performance Racing Engine which can be reconfigured by reprogramming the Fuel Injection, Timing, and Varying the Mixtures for Barometric Pressures and Relative Humidity just moments before the announcement to Start your engines, ... you might have reason to Index the Plugs.

If you have BURIED Plugs, ... requiring the removal Body Panels, Intake Plenum, Coil Modules and Disconnecting Motor Mounts too Rotate the Engine Block to access the Plugs: Long Lasting Iridium Plugs are in order.

But we have Engines which allow for the Plugs to be removed and discarded then replaced with New Plugs without fuss. Performance wise, we got nothing.

Making a choice of what Plug you use is wholly dependent upon what the Advertising Agency has led you to believe makes their clients Spark Plug better than Brand-X in the space behind your eyes between your ears.

It all depends on factors like:
Your favorite color.
Lighting Bolts.
Mushroom Clouds
Wild Horses stampeding.
A Formation of Jet Aircraft

And, ... Last ---> But not LEAST!

Just how much you are willing to spend to see the bearded lady.

 

I disagree, I have a tray full of Platinum plugs that would be worth Twenty Grand, easy, if Platinum were the MAIN Component.

It's a short, 1/4 inch wire at the very tip, fused to a conductor in the insulation.

No - it's not an alloy, it's a copper CORE inside a STEEL electrode. It may be true that the electricity finds the copper path easier, after crossing the air-gap, but the firing + terminal is steel.

In fact - I don't know how they do it - embedding the copper into steel, blending special ceramics that transmit heat without cracking, rolling the threads, electro-plating the housing to prevent rust, welding the side electrode, stamping or imprinting the logo and info - - then selling it for $0.99 !! A spark plug is worth about $35.00 !!

I sincerely hope you will stick around so we can learn alot from you.
And I have no formal electrical training.

 

Anyone old enough to be a GENUINE Eyewitness to the Birth of Rock-'n-roll; should remember getting ready to go-out on Saturday Night.

Clearasil
Brylcreem
Old Spice
Platinum's

http://www.goantiques.com/detail,ultrex ... 34447.html

 

somebody tell me about this "spark gap" inside a plug

 

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"Our sticker is bigger than their sticker. We give you two."

"Our Plugs are Guaranteed to make you go further, faster, save gas, make you popular with chicks and last a lifetime because they never wear-out and come with a sticker for every one you buy."**

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This is a freaking cool thread. I was just gapping spark plugs for the first time for a friend's XJ, and wondering how it could possibly matter--such a small difference, surely the bike wouldn't notice!

Timing. Of course. Crazy. So running rich should increase impedance on the arcing tips, which should cause a need for more voltage to arc, which should also kind of screw with your timing a bit, no?

ttride: yeah, there's lots of stuff like that. For instance, buying a machine that took Ph.D's to engineer, metals dug up from the earth from all over the world, purified, treated, measured down to hundreds and thousandths of an inch, assembled by further machinery specially designed to do so, etc., etc., all for only a couple hundred bucks--after international shipping?

These bikes are pretty ridiculous. It's a fun game to think about what things you can get for less than $5 that required an assembly process involving precise manufacture and parts from around the globe. Weird economics, this world...

 

Rick, agreed. I like mushroom clouds and plane formations, they make me feel cooler and make my bike a sex object.

I bought the regular ol' NGK BP7ES. Plain. Simple. Specified. (That is what was specified, right?)

TIME, I didn't write that well. I meant "the iron or steel inside the copper-type plugs is a poor conductor, relative to copper." I didn't mean to suggest that the iron or steel were physically inside the copper, either as an alloy, or just meaning the copper was coating them.

And by "making up the bulk" I misspoke a bit, too. I mean making up the bulk of the conducting path. However, I suppose with platinum and iridium they are just coatings on the outside of probably a copper core, just like "copper" plugs. The platinum or iridium are used since they have higher melting points resulting in less sputtering and longer life. This also allows manufacturers to make the tips smaller, thus focusing the electric field for more control over the spark. But again, this will affect timing and energy in the spark. Finally, they also make the tips smaller so that they will absorb less heat in the first place. Although, that seems silly to me, because they will eventually absorb heat once things warm up, but now the tip being small is also what causes it to lose heat more slowly.

Yeah, I'm utterly amazed at the many things we manufacture in the world and the price we sell them at. I think my plugs were $8+ after tax for four. And if you look at a cross-section of plug design... woah.

Polock, I've not found a design or patent file showing it, but I've heard before about the air gap inside a spark plug. But since I can't find something I'm skeptical of its existence. But the theory behind using one is common in a lot of pulsed power work where we use spark gaps. I'm talking BIG spark gaps and trying to reach multiple megavolts. Loud, sometimes destructive (and obviously cool) stuff!

The idea is, you put two spark gaps in series. The 2nd gap to see the voltage across its terminals is typically setup such that it would normally fire at a much higher voltage than the 1st gap. However, spark gaps can be very sensitive to dV/dt (the rate of change of voltage over a specified time, or sometimes erroneously called just "rise time"). So you charge up gap 1 to the lower voltage, and you can do so slowly from a low-power supply. Spark gap 1 breaks down and conducts, thus increasing the voltage at the second gap VERY rapidly, and now the second gap will fire at a voltage much lower than typical, just because it happened so fast. Seen it, built it, done it. I've read the physics behind it once and it has to do with electron-hole migration and dipole moments of the gas inside the gap. Physics is truly an under-loved science. If we want our kids to learn and do amazing things to advance science, we simply need to get rid of all these safety rules and get them back into blowing crap up in school!!!

Anyway, point is, that first gap helps regulate the second one. By controlling the geometry of the second gap and the connection to it (and the dielectric around it and a few other things) you can "regulate" much better how and when that second gap fires. So, it would make sense to employ something like this in spark plugs because minor variations in coil windings and their iron or ferrite cores that could change arcing voltage a few hundred volts are now factored out and dominated by other effects.

fintip, I hadn't thought of that, but theoretically, yes, fuel/air mixture changes the gas composition which would change the arcing voltage and thus the exact time at which the arc occurs.

The thing to keep in mind is what effects dominate and what effects are miniscule. Which ones do and don't are beyond me!!!

 

The air-gap thing is an old shade-tree mechanic's trick to get an oily or fouled plug to fire:

Simply cut the plug wire about 2" away from the plug, and tape it to a popsicle stick with about 3/8" gap between the two cut ends.

CBE (crude but effective) it does work.

 

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