I have kept quiet for a long time about the iridium plug debate on here but I am going to throw in my $.02... These findings are based on on-time data logging and research on a turbo'd 400whp audi a4 (2871R), but I see no reason why this wouldn't carry over to 2 stroke applications...especially the boosted guys.
Copper is one of the best conductors of electricity and heat, but they just plain dont last mileage wise. Iridium & Platinum last 10 fold longer thus the reason why auto manufactures use these. Coppers can last 5K miles if the engine is operating optimally. Platinum and Iridium plugs have a center electrode (fine-wire) that is thin. Under high boost application they get so hot they will begin to "heat glow" and cause premature ignition in the combustion cycle (pre-ignition => detonation) unless they were properly designed to pull the heat. This is a problem for all of the turbo guys running high boost. Copper on the other hand, has a much thicker center electrode, on top of that, the copper material is able to dissapate heat from the combustion chamber fast enough to keep the combustion temperatures lower. Coppers use thicker electrodes simply based on the fact that they can easily jump the spark, whereas platinum and iridiums will require a fine wire to better direct the spark to prevent missfires.
Remember the TWO primary functions of a sparkplug:
1) To efficiently ignite the A/F mixture without missfires (gap..etc)
2) To pull heat from the combustion chamber into the head, where the cooling system should dissapate that heat. (Heat Range)
A platinum/Iridium plug in a colder heat range usually runs just as hot as a copper in the standard heat range when under high stress. So many people will use a Platinum/Iridum plug TWO steps colder to counter that. But using a plug that is 2 steps colder, will lead to two things:
1) More prone to carbon-fouling on "normal driving" where EGT's are kept low. (Plugs must stay above 550C Deg to burn off excess carbon deposits to "self-clean")
2) As a result, loss of horsepower from a less efficient/inhibited spark.
You need a plug that is actually "hot enough" to ignite the A/F mixture as hot as possible to get the most efficient combustion, as well as burn off carbon-deposits (~550C deg), and yet cold enough to prevent pre-ignition when compression is high (< 870C Deg).
Copper is one of the best conductors of electricity and heat, but they just plain dont last mileage wise. Iridium & Platinum last 10 fold longer thus the reason why auto manufactures use these. Coppers can last 5K miles if the engine is operating optimally. Platinum and Iridium plugs have a center electrode (fine-wire) that is thin. Under high boost application they get so hot they will begin to "heat glow" and cause premature ignition in the combustion cycle (pre-ignition => detonation) unless they were properly designed to pull the heat. This is a problem for all of the turbo guys running high boost. Copper on the other hand, has a much thicker center electrode, on top of that, the copper material is able to dissapate heat from the combustion chamber fast enough to keep the combustion temperatures lower. Coppers use thicker electrodes simply based on the fact that they can easily jump the spark, whereas platinum and iridiums will require a fine wire to better direct the spark to prevent missfires.
Remember the TWO primary functions of a sparkplug:
1) To efficiently ignite the A/F mixture without missfires (gap..etc)
2) To pull heat from the combustion chamber into the head, where the cooling system should dissapate that heat. (Heat Range)
A platinum/Iridium plug in a colder heat range usually runs just as hot as a copper in the standard heat range when under high stress. So many people will use a Platinum/Iridum plug TWO steps colder to counter that. But using a plug that is 2 steps colder, will lead to two things:
1) More prone to carbon-fouling on "normal driving" where EGT's are kept low. (Plugs must stay above 550C Deg to burn off excess carbon deposits to "self-clean")
2) As a result, loss of horsepower from a less efficient/inhibited spark.
You need a plug that is actually "hot enough" to ignite the A/F mixture as hot as possible to get the most efficient combustion, as well as burn off carbon-deposits (~550C deg), and yet cold enough to prevent pre-ignition when compression is high (< 870C Deg).
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