Denso IK20 iridium spark plugs – not impressed

[CHECKERED]

This isn’t a review of the IK20 for the S4 but rather what happens to them after 64K miles.

These were installed in my altima for the last 6 years, both the S4 and Nissan use the same IK20 0.044 gap spark plugs, similarities between the engine: dual overhead cam, 11:1 CP, similar displacement per cylinder 525cc vs 550cc, the main difference is the electronic ignition, coil on plug on the audi vs the distributor on the altima.

I was prepping my car for a road trip to northern California and in the process of checking every fluid, bolt, and seal I pulled the spark plugs.
The iridium plugs are advertized to last 100K miles and denso even goes as far as to point out that Lexus uses their long life iridium plugs the don’t need replacement until 120K, well I’m glad to report its all marketing BS…

Here is a brand new IK20 plug (on left), Notice the U shaped grove that goes all the way down the ground electrode.





Here is a plug after 64K miles, lots of hard driving and track days.







Notice the iridium tip itself is intact and in good condition but there is no more grove where the spark makes contact, that part has been worn down, there is a small amount of metal missing/worn out at the very edge of the tip, the current gap is 0.052-0.053, it is not recommended to re-gap these.

Recently (last 5K miles or so) the car has been harder to start and idle a bit choppy, these should have been replaced at 60K, similar interval as regular platinums, so the platinum ground w/iridium electrode doesn’t last any longer then a regular platinum plug, the premium for iridiums does not justify the extra cost, stick with OEM, and if you are looking for some more performance and don’t mind replacing your plugs often; copper is your best bet.

[B6JoeS4]

Who's your daddy now single-lash fanboys?

[CHECKERED]

haha...I’ll admit that the iridiums are not what they are cracked out to be…contrary to my prior posts

[SquiddyB6S4]

Who's your daddy now single-lash fanboys?

For the record, what he said is that the long-life part is bullshit. He didn't say that the car ran poorly from the start. Just stating the obvious: 64-5=59, so for 59k miles he had no problems to report.

Personally, I don't care what the advertisement says about spark plug life - mine go the way of the dodo every 30k or less. It's like oil changes - why stretch it as far as possible when it's relatively cheap and very important to the engine's health? Besides, mostly the people who tell you the life of the plugs are people who have money to be made on a long service interval, so why on earth would you take their words for it?

As for selection of plugs (and plug technology, and materials, etc), it's entirely debatable. Lots of guys run the OE stuff and like them, and at least some people don't run the OE stuff and also like them. I don't think there is a right and wrong answer with plugs, personally. I've run all kinds of plugs in many different kinds of motors, and the resounding theme is that proper gap is paramount, and generally newer plugs are better than older plugs, hence my preference to change frequently and not wait for them to wear out.

[CHECKERED]

That is an excellent point. The plugs themselves were fine when new, the main improvement was going from an old plug to a new one, but once you get new plugs they all feel fairly similar (plat, copper, iridium)

If I could make a recommendation, a copper plug that is changed every 4-5K miles will give the best results, in both performance and mileage.

They are so inexpensive that you’ll end up spending the same amount of money (if you do them yourself) and you’ll have new plugs every 5K miles, which is far better than any pricy 30K+ miles plug.
I just gave the altima copper plugs @ $2.08 each you can’t go wrong.

Also JHM went with colder copper plugs for the supercharger application, I don’t know how long they will last under boost, Jason told me so far he has 10K miles on his…don’t know if I want to go to such lengths and would probably end up changing them with every oil change: 4-5K miles.

[dparm]

Umm, Denso says that with the 0.4mm iridium tip you are supposed to change every 30k. This is stated pretty clearly.

[dparm]

That is an excellent point. The plugs themselves were fine when new, the main improvement was going from an old plug to a new one, but once you get new plugs they all feel fairly similar (plat, copper, iridium)

If I could make a recommendation, a copper plug that is changed every 4-5K miles will give the best results, in both performance and mileage.

They are so inexpensive that you’ll end up spending the same amount of money (if you do them yourself) and you’ll have new plugs every 5K miles, which is far better than any pricy 30K+ miles plug.
I just gave the altima copper plugs @ $2.08 each you can’t go wrong.

Also JHM went with colder copper plugs for the supercharger application, I don’t know how long they will last under boost, Jason told me so far he has 10K miles on his…don’t know if I want to go to such lengths and would probably end up changing them with every oil change: 4-5K miles.

Know why they went for copper? Here are some of the thermal conductivities of some commonly used metals (Watts / centimeter*Kelvin) :


Zinc = 1.16
Aluminum = 2.37
Copper = 4.01
Steel = 0.70 - 0.82
Platinum = 0.716
Iridium = 1.47


So yeah, copper kicks ass. Sadly, the melting points are nearly the inverse so they don't last worth a shit:

Zinc = 420
Aluminum = 660
Copper = 1083
Steel = 1400-1500
Platinum = 1772
Iridium = 2410


A true iridium plug, like Denso's, surpasses platinum in most areas. They can make the electrode very small without risk of it melting right away. The ultra-sharp tip gives you a very good spark.

Unfortunately, the ultra-fine electrode in the IK20 "performance" version will not last very long. The 0.4mm is the smallest ever made; most of the other iridium tips are bigger for longevity. Denso explicitly states that you must replace it every 30k or sooner. A more generic iridium with a larger tip, like Toyota uses, will easily go 100k+.

[dparm]

For the record, I have been running that exact plug in my car. I change them once a year; when used with a coupon at Autozone or whatever, you can get them for like $4/plug. My last set came out and could've probably gone right back in, but I just replaced them anyways.

[SquiddyB6S4]

Also JHM went with colder copper plugs for the supercharger application, I don’t know how long they will last under boost, Jason told me so far he has 10K miles on his…don’t know if I want to go to such lengths and would probably end up changing them with every oil change: 4-5K miles.

I've heard LOTS of people swear by copper for boosted applications, and for that reason. I haven't always used copper on my boosted motors, but I've never run more than 12psi. If I did, I'd have only run Cu.

[dparm]

Copper works very well in NA, too, per my post above. You just have to change them very frequently. Serious racers will swap plugs after every race since copper is so cheap.

Back in my Honda days the guys with track-prepped Integra Type Rs used to do that routinely. I swore they bought the plugs by the gross...

[Ill 3.0]

No perfect choice, they all have their drawbacks. I've been using coppers for a few years and just replace every 5k miles when I change my oil. It adds a little bit of time, but then you never have to worry about them and its fairly cheap.

OT, did JHM experiment with reducing the gap a little on their supercharged applications? Stage I is about 6 psi? Might be enough to reduce it a bit, IDK.

[SquiddyB6S4]

OT, did JHM experiment with reducing the gap a little on their supercharged applications? Stage I is about 6 psi? Might be enough to reduce it a bit, IDK.

IDK, but my SR20(DET) and my B20(s/c) taught me that low boost, 6-7psi, doesn't usually need a plug change. Upped it to 12psi and went 1 heat range colder on the NGK scale, dropped the gap a tiny, tiny bit (I want to say .004"), nabbed a bigger intercooler, and it ran great with no issues other than frying the clutch almost immediately.

[Ill 3.0]

a tiny, tiny bit (I want to say .004"),

Yeah, I was thinking in this range. Something small just to see how the motor reacts. Probably won't matter for the Stage I guys, but maybe Stage II and above something to think about.