Iridium Plugs - what are the specific issues?

[Parkinen]

The "reduced spark voltage requirement" thing you keep quoting is a bit of a red herring. While iridium plugs do take less voltage to fire, that's in comparison to platinum, not compared to standard copper plugs. I couldn't find any information regarding how much voltage iridium requires compared to copper or silver.

Yeah I've been looking too and can't find many actual numbers. That Weaponx "white paper" I found (which by the way goes into some detail) does compare fine wire Iridiums to copper plugged, nickel/alloy center electrode plugs (2.5mm diameter).

Based on their rough graphs it looks like ~18kV to ionize a nickel plug and maybe ~15.5kV to ionize the Iridium. They go on to explain though this has nothing to do with the actual material but owes its lower voltage to the smaller diameter electrode which they're able to get away with because of the hardness of the Iridium.

This is all I've found thus far:

http://www.weaponxperformance.com/techn ... ECH_V1.pdf

They also talk about ignitability for 2.5mm Ni/Chrome dropping off around 15:1 AFM vs fine wire Iridium which starts to drop off around 17:1...interesting to say the least.

I don't think that these are better plugs than the plugs designed for the system, but if this trend keeps going it might be a coincidental improvement for older ignition systems.

[Parkinen]

Here's another one that looks at voltage in terms of electrode diameter. Different numbers though.

Looks like ~35 kV for 2.5mm and ~25kV for .6mm

http://www.globaldenso.com/en/products/ ... script.pdf

They're also showing ~21.5:1 AFM for ignitability...

[Blue Shadow]

If the plugs fire, what does it matter if they would have fired with less voltage? I guess it is good for an old, tired, and failing ignition system but for one that works for the Silvers what improvement will a lower voltage capable spark plug have to offer?

[Jeremy]

If the plugs fire, what does it matter if they would have fired with less voltage? I guess it is good for an old, tired, and failing ignition system but for one that works for the Silvers what improvement will a lower voltage capable spark plug have to offer?

One of the theories about why platinum plugs don't work well in these cars is because of their need for a higher voltage to spark properly. If Iridiums have a spark voltage close to silver/copper they could be a viable replacement for Silbers should they become difficult to acquire.

[Mike W.]

If the plugs fire, what does it matter if they would have fired with less voltage? I guess it is good for an old, tired, and failing ignition system but for one that works for the Silvers what improvement will a lower voltage capable spark plug have to offer?

One of the theories about why platinum plugs don't work well in these cars is because of their need for a higher voltage to spark properly. If Iridiums have a spark voltage close to silver/copper they could be a viable replacement for Silbers should they become difficult to acquire.

Coppers work as well as Silvers but don't last as long. I think the NGKs are copper and they still do quite well.

[Jeremy]

It doesn't hurt to have options.

[turbodan]

Iridium plugs are designed for longer change intervals. Copper plugs require a large diameter electrode due to the speed at which they wear. Iridium is far more resistant to erosion due to the nature of the material, so the electrode can be much smaller and still last much longer. The smaller tip makes the plug less likely to foul and makes the spark more consistent. I've seen many of these things come out of motors after over 100K miles and the only wear is on the ground electrode.

I don't believe the material of the tip of the plug has nearly as much of an effect on how hard it is to fire the spark than the width of the gap. Thats nothing to worry about. If the plug gap and heat range are correct there is no reason a plug would not work correctly regardless of design. I've used several kinds of plugs in M20's with gaps from large to quite small without any problems. I've used several kinds of nonstandard plugs in other engines without problems. Some things like spark plugs and gas really inspire mysticism and speculation. The expensive plugs just last longer. Some fancy plugs are poorly designed and don't work well in any application. Thats really it. Do not fear iridium plugs.

[Parkinen]

I think its important to note that (at least in the case of NGK) every single spark they produce is copper cored, and to say a spark plug is "copper" is slightly inaccuurate. Apparently, and I didn't know this until I stumbled across this document, the material listed for a certain plug is usually just the material of the electrode. In the case of "standard copper plugs" this is actually a nickel alloy as copper (although a superior conductor) is crap under stress and heat. So even a "copper" plug uses a hardened alloy of another metal for the electrode. This means that even a platinum or iridium plug is also a copper plug.

What we should really be discussing is electrode material, and more specifically electrode size, as that seems to be a big component when considering the performance of a plug.

This might be old news to a lot of you but I honestly had no idea until I looked into it. Hopefully this is helpful to some folks in the forum.

[slimdevil27]

Oh can of worms......

High compression engines, precise fuel control/afm, with high energy ignition use platinum/iridium.
Low compression, carbureted/batch fired fi, map or AFM, low energy igntion use standard plugs.

Now the why...

Platinum and iridium are designed to be used in high energy ignition systems yet require less energy to ionize the gap. Remember ohms law amperage and resistance are inversely proportional. Resistance in an ignition system prolongs the time that the spark is jumping the gap, spark duration. If the duration of the spark is too short the result is incomplete combustion, or a flat out misfire. Due to turbulence in the combustion chamber the spark needs to last long enough to overcome this turbulance and ensure even flame front propagation.

So a low voltage ignition, like ours, uses a plug with a higher resistance and the result is the correct amount of spark duration for consistant ignition.

Take that same igntion system and reduce the plug resistance...the result is a shorter spark duration, less consistant igntion and an irregular flame front propagation from the spark kernal. Excessive carbon deposits and fouling typically associated with weak ignition ensues and your miricle plug is garbage.

If you use a standard plug in a high energy ignition designed for platinum/iridium the higher resistance increases the spark duration....and the engine runs just fine. However the longer duration causes excessive electrode wear for no performance gain.

Do not use platinum or iridium plugs unless called for by the manufacturer.

[Parkinen]

Oh can of worms......

High compression engines, precise fuel control/afm, with high energy ignition use platinum/iridium.
Low compression, carbureted/batch fired fi, map or AFM, low energy igntion use standard plugs.

Now the why...

Platinum and iridium are designed to be used in high energy ignition systems yet require less energy to ionize the gap. Remember ohms law amperage and resistance are inversely proportional. Resistance in an ignition system prolongs the time that the spark is jumping the gap, spark duration. If the duration of the spark is too short the result is incomplete combustion, or a flat out misfire. Due to turbulence in the combustion chamber the spark needs to last long enough to overcome this turbulance and ensure even flame front propagation.

So a low voltage ignition, like ours, uses a plug with a higher resistance and the result is the correct amount of spark duration for consistant ignition.

Take that same igntion system and reduce the plug resistance...the result is a shorter spark duration, less consistant igntion and an irregular flame front propagation from the spark kernal. Excessive carbon deposits and fouling typically associated with weak ignition ensues and your miricle plug is garbage.

If you use a standard plug in a high energy ignition designed for platinum/iridium the higher resistance increases the spark duration....and the engine runs just fine. However the longer duration causes excessive electrode wear for no performance gain.

Do not use platinum or iridium plugs unless called for by the manufacturer.

Ok but the NGK IX (fine wire iridium series) specified for our engines, for example, uses a 5k ohm resistor and requires about 20% less voltage to ionize than a Bosch WR9LS which uses a 6k ohm resistor.

Whats the difference between using a plug that was called for by the car manufacturer (almost 30 years ago) and a new plug that is designed for the engine by a very reputable spark plug manufacturer?

The latter also offering 3 times the longevity and almost 50% better lean limit ignitability (which is just basically an insurance policy against engine damage), and identical flame propagation.

Maybe it's just me but I don't see the point in ignoring advances in technology if they are tailored for specific application.

No one is touting a miracle plug, just a potential improvement. You say not to use platinum or Iridium plugs unless called for by the manufacturer, but which manufacturer is that? The one that stopped engineering development of our engines over 20 years ago or the one that has figured out that maybe there's a way to improve upon an already great design?

[wkohler]

Why don't you just go buy a set and see how they work for you on your 100% baselined M30?

[Jeremy]

Why don't you just go buy a set and see how they work for you on your 100% baselined M30?

This is the best policy. We could all talk and theorize it all to death, but the proof is in the pudding really.

[Mike W.]

Why don't you just go buy a set and see how they work for you on your 100% baselined M30?

This is the best policy. We could all talk and theorize it all to death, but the proof is in the pudding really.

Great minds think alike, I suggested the same in including him in the list of people not to advise.

[tn535i]

In debates like this which remind me of some oil discussions, I steadfastly assert that some kind of spark plug is better than no spark plug just like some kind of oil is better than no oil. Someone will disagree with that I suppose.

I'm with WKohler and can I quote myself?

Buy them, run them, let us know.

Maybe some day, and time will tell, a new design is proven both backward compatible AND better and obsoletes the old one. I rarely get on that page as my cynical self normally assumes there is a move to obsolete all things old with something more profitable!

[wkohler]

wkohler endorses the use of flicker corks to help promote compression and combustion.

[Parkinen]

Sorry guys I'm not trying to be argumentative or pedantic. I apologize if it seemed that way. I just started digging on this and got some answers that seemed a little too simple, and it seems the more I dig the more I learn.

I've been running a set of NGK BPR5EIX for just about a week now and so far so good. The WR9LS set I pulled out must only have about 5k on them, they looked pretty darn fresh so I'm sure I can throw em back in if something comes up.

As wkohler so graciously pointed out the car isn't 100% baselined, but I haven't changed anything except the plugs since I installed them. So far I've noticed that the idle is much smoother. I'll get milage numbers as soon as I fill up again.

[Parkinen]

Why don't you just go buy a set and see how they work for you on your 100% baselined M30?

This is the best policy. We could all talk and theorize it all to death, but the proof is in the pudding really.

Great minds think alike, I suggested the same in including him in the list of people not to advise.

Hey c'mon don't chide me for being inquisitive and digging up actual information about this. That's not fair.

I wonder how many of the people who've given their opinion regarding this thread previously knew any the stats on the fine wire Iridiums that I dug up, let alone run them in their car to see how they do.

As far as I can tell the people who've actually tried them have no problems with them and the people who haven't say to stay away...

[tn535i]

I was not. I think most have no problem with asking questions and turning up new information. I appreciate that others do that and also learned a lot about plug design and operation from the discussion and info posted. Discussion/debate is good and maybe Iridium is fine. IDK. I know I once ran first gen Platinum plugs in our e30 M20 for a long time with no trouble at all until I had CTS problems and the plugs compounded that when they fouled easily. Just a hint of rich condition and it would miss almost completely. I first cleaned then changed plugs before then figuring out the CTS was the real culprit. Probably could have put the Platinum back but never did. So the acid test of the Iridium plug IMO would be how well it copes with a CTS or other issue causing it to run rich. Do they deal with that OK or foul much easier because the electrode is tiny? Someone want to try it with 1/2 and 1/2 Iridium and Silver?

[Jeremy]

You might want to go back and read about my experience with them on my turbo car for at least one anecdote concerning that.

[CharleyDog]

The adage "drinking your own bathwater" comes to mind. Someone should take a hit for the team and call Champion's technical service line (800-325-8886) and drill their way into that corporation until they find someone who can answer these questions.

It'll be fun to watch, anyway.

[Curtispsf]

Interesting thread. I'll be trying a set of NGK Iridium IXs in my 88 M5 and will report back. I suspect (yawn) that there will be nothing to report. They work.

[spinedocab]

..... The iridium shit is simply a sales gimmick. Ooooooo, they sound exotic! Let's spend $10 each on them.

Not necessarily. I thought that too, but about a year ago I bought my Aunt Phyllis' old car for my daughter to drive. The car needed a few points of deferred maintenance and some gasket and seal restoration. When I took out the 176k mile original, iridium plugs I was amazed at the excellent condition of these old sparkers. Near perfect. So when I replaced them I put new versions of those old plugs in there. Why screw with success?

If you'd like I can post photos of those plugs. They're unbelievable. 14 years and 176,000 miles.

All that said, I'd still not probably put them in an old M30. WR9LS ftw.

AB

[Patrick McHugh]

Your next topic should be about oil brands

[Patrick McHugh]

AND AFTER THAT TIRE BRANDS

[Patrick McHugh]

But lets not forget a question about the FCP groton suspension overhaul kit

[Patrick McHugh]

But first let's argue about why the car is shaking at 48 MPH

[Mike W.]

But lets not forget a question about the FCP groton suspension overhaul kit

AND AFTER THAT TIRE BRANDS

Your next topic should be about oil brands

How about URO brand parts?

[slimdevil27]

What stance is right for 20's?

[Coldswede]

What stance is right for 20's?

Up on blocks, with the dubs stolen.

[Parkinen]

no problems to report..yet