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I've been hearing a lot about iridium spark plugs lately. I have read claims that these plugs are more durable than copper plugs due to iridiums high melting point and anti-corrosive properties, but what I'm wondering is, how much better do they perform in real life? Not just on paper. Is the difference in their performance life large enough to justify the price difference? (especially for a top end brand)

Some difference described in this post

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I think it is a duplicate of the one you linked to, unless you are asking something different? – Rory Alsop May 2 '12 at 10:41
@RoryAlsop, I tend to agree - it's not immediately obvious that this question isn't a duplicate of the previous. Perhaps if the question was repurposed to something more like "How much longer than a copper plug will an iridium plug last in car X?" – Bob Cross May 2 '12 at 11:01
@BobCross I have updated my question to your example title, seeing as it is a more fitting title, and Rory I am asking something different. The linked post is asking the differences, whereas my question was trying to focus more on how the differences between the plugs weighed against the cost difference. – Mick MacCallum May 2 '12 at 11:17
Teeny edit to add the question mark. I think this is a good question: I'd be interested to know myself. – Bob Cross May 2 '12 at 12:15
@MDT - that change works for me. Would agree it is now a different question. – Rory Alsop May 2 '12 at 14:01
up vote 1 down vote accepted

Per most service manuals:

Iridium 100-120k miles

Copper 20-30k miles

The coppers used to be commonly found on turbo cars and can wear out much faster with "spirited" driving.

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