NGK Iridium spark plugs (IX) vs Denso Iridium spark plugs, Which is best? This article compares the basic construction differences, the claimed benefits and the price.

Iridium Spark Plugs – Service Life

NGK Iridium spark plugs in our experience last literally years, we have been running as set for well over 100,000 miles with no obvious signs of wear on the electrode. The conductor does display wear and we have had to adjust the plug gap because of this. The actual iridium electrode looks like it could last the life of the car.

Denso Iridium spark plugs use a much thinner electrode than even the NGK. Given how long the NGK electrodes last you could argue the NGK are over engineered and reducing their diameter would have no effect on their service life.

In theory, the Denso iridium spark plugs would not last as long because the iridium electrode is not as thick. Is the difference going to be noticeable? Probably not.

In any case, in our experience, iridium spark plugs will outlast platinum spark plugs a few times over.

Iridium Spark Plugs – Power & fuel Economy

Denso claim the small electrode conducts easier leading to a more powerful spark. They have marketing material on their website showing Denso iridium spark plugs can improve fuel economy and power. Is it going to be noticeable in day to day driving? I doubt it.

One thing I can say about swapping to Denso Iridium from NGK Iridium is that the engine appears to start easier however, this could be down to the NGK having well over 100,000 miles on them. Having said that, there were no running issues with the NGK I simply swapped then over to try the Denso.

To my knowledge NGK do not mention any power of fuel economy gains from their iridium spark plugs but if the assertion from Denso is true ie a smaller electrode leading to a more powerful spark then in theory the NGK should give similar benefits.

Iridium Spark Plugs Price

So the performance difference is probably not noticeable but service life will probably be much longer than platinum spark plugs what does this mean for the price? Are iridium spark plugs generally good value?

This will depend on the engine and how many spark plugs it uses.

If we use a hypothetical example, say platinum spark plugs cost 2 dollars each and the equivalent iridium cost 9 dollars each. Are iridium spark plugs worth 4.5 times more than platinum?

In my experience, solely from a service life perspective, yes. I would change my platinum spark plugs every 12-24,000 miles, maybe I would change the iridium plugs every 100,000 so the net cost difference in zero but I get the “claimed” benefits of running iridium plugs.

Iridium electrodes are much smaller in diameter than platinum yet last much longer

Labour costs/time

I have seen platinum electrodes last less than 12,000 miles, the problem being the electrode wears away. On that particular engine I had to adjust the plug gap every few months. With iridium plugs on the same engine once a year was enough. From a time saving point of view, in this case, the iridium plugs paid for themselves.

And this was on an engine where the spark plugs were easy to change.

Tricky Engine

If servicing the spark plugs on your engine is a bit of a chore then switching to iridium spark plugs is a complete no brainer. Imagine how much time you would save checking or changing your spark plugs three times less often


And if your engine consumes spark plugs, gapping them regualrly will be important for best performance. With iridium plugs your engine will also be running better for more of the time.

NGK or Denso

In my opinion the biggest reason by far to switch to iridium spark plugs is the money and time you save in not having to service and replace your spark plugs so often.

From this perspective NGK would have to come out on top because the electrode has more material which in theory means they would have a longer life than Denso, making the savings from using NGK bigger.

If the marketing from Denso is accurate you may get the best of both worlds, the iridium electrode is going to last a very long time anyway plus you get the claimed performance benefits. But would the performance difference between Denso and NGK be noticeable? I doubt it, although I did personally notice the easier starting but I was not comparing new with new.

Price Difference

The decision between Denso Iridium and NGK Iridium will more than likely come down to price. Generally I see Denso iridium spark plugs costing around 30% more than NGK. If that is a big difference for you then choose the NGK, if it makes no difference to you I don’t think Denso would be a bad buy either.

Like the videos?

Sign up to receive awesome content in your inbox, every month.

We don’t spam! Read our privacy policy for more info.

One thought on “NGK Iridium vs Denso Iridium Spark Plugs”

Leave a Reply

Your email address will not be published. Required fields are marked *

three × 2 =