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Spark Plug Heat Range

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I friend picked me up a Denso Iridium plug IU27.

Its one increment colder than the plug recommended for the DRZ400 which is IU24

DENSO heat ranges move up as they get colder; 16 would be our hottest Iridium Power plug, 34 would be our coldest (ranges; 16,20,22,24,27,31,34)

http://www.densoiridium.com/faq.php

The bike operates in a hot humid climate and has BB/Cams/one layer base gasket engine mods.

Can I use the colder IU27 plug or should I stick with the recommended IU24 ?

Would there be any advantage for me to use the colder IU27 plug ?

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always use the hottest plug you can. colder plugs than necessary wont burn the fuel as fully/completely

same with gap, start big, and work your way down as needed.

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i use the colder plug

Chooken

What was your reason for choosing the colder plug ?

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I can't speak for chooken but where we are, it can get to over 35C/95F with the air very hot and still.

So I run a cooler plug (9 in a NGK) to keep internal temperatures down, I will revert back to the standard plug when it starts to cool down next year.

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I should keep my mouth shut but -- Heat range of a plug has no affect on engine temperature. Heat range has only to do with the temperature that the tip of the plug operates at. Too hot the tip melts, too cold the plug does not burn off the contaminates.

Heat range of the plug has nothing to do with igniting the mixture. (assuming the plug is not cold fowled or heat melted)

The temperature that the plug runs at has a lot to do with how the motor is operated. High load such as wide open throttle under racing conditions often requires a colder plug.

Personally I would run as cold a plug as operates cleanly and does not have a tendency to fowl and I would gap it to manufacture's recommendation.

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Sorry Noble but you can not have it both ways,

Quote:Heat range of a plug has no affect on engine temperature.

Quote:The temperature that the plug runs at has a lot to do with how the motor is operated.

So if the motor is being operated at high revs and/or load it will create more heat, hence it can cause an increase of temperature at the spark plug tip, correct?

There is a bit of what come first there, chicken or the egg.

Surely engine temperature is exacerbated by an increase in ambient temperature, even allowing for a water cooled motor with a thermostat there comes a point where a motor can no longer be kept cool.

If the heat range of a plug has no effect on engine temperature, why would you run?

Quote: as cold a plug as operates cleanly and does not have a tendency to fowl

I'm not looking for an argument here just clarification.

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I will try to clarify.

"If the heat range of a plug has no effect on engine temperature, why would you run?

Quote: as cold a plug as operates cleanly and does not have a tendency to fowl"----To protect the plug from possible over heating not the motor. An over heated plug can crack the insulator or melt the tip. Either one will cause a motor to perform poorly or possibly damage the motor. Selecting the correct heat range of plug is to protect the plug and in turn keep the motor operating at peak efficiency. A spark plug that operates too cold does not burn off contaminates and will eventually cold foul.

"Surely engine temperature is exacerbated by an increase in ambient temperature, even allowing for a water cooled motor with a thermostat there comes a point where a motor can no longer be kept cool."---- Yes, no argument there. But that has nothing to do with spark plug heat range.

"Quote:The temperature that the plug runs at has a lot to do with how the motor is operated.

So if the motor is being operated at high revs and/or load it will create more heat, hence it can cause an increase of temperature at the spark plug tip, correct?"-----Temperature of combustion and temperature of the motor are certainly related. There is fire in the combustion chamber hot enough to easily melt the aluminum piston. But the piston does not melt because the heat is conducted away. It is also hot enough under full load to melt and damage spark plugs. But it doesn't as long as the spark plug is cooled. The "heat range" of a spark plug is a measure if its ability to transfer heat away from the tip of the plug. A cold plug transfers heat more rapidly than a hot plug. Under high load conditions, a "colder plug" will be cooler at the tip than a "hot plug" under the same operating conditions. We are only talking about the retained heat at the tip of the spark plug sitting right in the middle of the combustion flame. A colder plug will not make the heat of combustion any less.

If you Google for info on spark plugs and how internal combustion engines operate you may be able to find better explanations than I can provide.

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I will try to clarify.

"If the heat range of a plug has no effect on engine temperature, why would you run?

Quote: as cold a plug as operates cleanly and does not have a tendency to fowl"----To protect the plug from possible over heating not the motor. An over heated plug can crack the insulator or melt the tip. Either one will cause a motor to perform poorly or possibly damage the motor. Selecting the correct heat range of plug is to protect the plug and in turn keep the motor operating at peak efficiency. A spark plug that operates too cold does not burn off contaminates and will eventually cold foul.

"Surely engine temperature is exacerbated by an increase in ambient temperature, even allowing for a water cooled motor with a thermostat there comes a point where a motor can no longer be kept cool."---- Yes, no argument there. But that has nothing to do with spark plug heat range.

"Quote:The temperature that the plug runs at has a lot to do with how the motor is operated.

So if the motor is being operated at high revs and/or load it will create more heat, hence it can cause an increase of temperature at the spark plug tip, correct?"-----Temperature of combustion and temperature of the motor are certainly related. There is fire in the combustion chamber hot enough to easily melt the aluminum piston. But the piston does not melt because the heat is conducted away. It is also hot enough under full load to melt and damage spark plugs. But it doesn't as long as the spark plug is cooled. The "heat range" of a spark plug is a measure if its ability to transfer heat away from the tip of the plug. A cold plug transfers heat more rapidly than a hot plug. Under high load conditions, a "colder plug" will be cooler at the tip than a "hot plug" under the same operating conditions. We are only talking about the retained heat at the tip of the spark plug sitting right in the middle of the combustion flame. A colder plug will not make the heat of combustion any less.

If you Google for info on spark plugs and how internal combustion engines operate you may be able to find better explanations than I can provide.

Thanks for that,

After doing some research, I have to agree you, it would be safe to say that we are not really gaining anything from a colder plug, except maybe for high speed or a modified engine.

I think now, getting the jetting right is more crucial than experimenting with spark plug heat ranges, not that I never worried about jetting, it has just been a habit of mine to put a colder plug in for the summer.

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