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I've noticed a lot of places sell cold spark plugs for the ST and I was wondering what the difference is between those and the stock ones. Why I would want to put those plugs in my car?
 

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One wants a 'correct spark plug for the conditions inside the cylinder.
The stock plugs are suitable for the average driver.
Colder plugs are for high performance use. IE: racing. Or the driver who is basically racing around all the time on the street.
The colder plug is for hotter cylinder conditions. Where the engine in under high RPM and heavy boost most of the time.
A 'colder' plug allow more heat to escape via the plug body. And thus stays at the correct design temperature in a 'hot' cylinder environment.

For the average driver, installing cold plugs will not be of any benefit at all. The colder plug will not warm up properly, and the colder plug will get full of deposits and STOP WORKING correctly in an engine not run hard all the time.
 

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Discussion Starter #3
One wants a 'correct spark plug for the conditions inside the cylinder.
The stock plugs are suitable for the average driver.
Colder plugs are for high performance use. IE: racing. Or the driver who is basically racing around all the time on the street.
The colder plug is for hotter cylinder conditions. Where the engine in under high RPM and heavy boost most of the time.
A 'colder' plug allow more heat to escape via the plug body. And thus stays at the correct design temperature in a 'hot' cylinder environment.

For the average driver, installing cold plugs will not be of any benefit at all. The colder plug will not warm up properly, and the colder plug will get full of deposits and STOP WORKING correctly in an engine not run hard all the time.
Thanks...

Note to self - keep driving like I stole it. :D
 

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http://www.ngksparkplugs.com/tech_support/spark_plugs/p2.asp?mode=nml

The heat range must be carefully selected for proper spark plug thermal performance. If the heat range is not optimal, then serious trouble can be the result. The optimal firing end temperature is approximately between 500°C (932°F) and 800°C (1472°F). The two most common causes of spark plug problems are carbon fouling (< 450°C) and overheating (> 800°C)
Read this and take the time to educate yourself.

The difference between a hot plug and a cold plug is the amount of insulation. Both require exactly the same amount of voltage to fire properly.

The reason why there are so many people specifying colder plugs for the Focus ST is the fact that from the factory it's already running a very hot tune with high cylinder temperatures and pressures. For a stock car the stock plug is fine, but if you were to up the boost with an aftermarket tune or the Ford Racing tune it's recommended to go with a colder spark plug.

For the Ford Racing Performance Pro-Cal tune and intake it requires a two step colder spark plug than stock as it drives the car very hard without the benefit of a larger intercooler.

For a Cobb off the shelf tune or a professional e-tune or dyno tune depending on the corrections and such you will likely want a 1 or a 2 step colder plug to prevent detonation and pre-ignition.
 

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"Fun Facts"

The difference between Hot & Cold for plugs is the length of the insulator between tip & contact with the metal "shell" of the plug.

Long insulator stays hot, because of the long path heat has to travel before reaching the colder wall of the shell.

For an extreme, some "Racing" plugs have an almost flat insulator at the tip - heat path straight to the wall to cool it as much as possible.

Peek inside the business ends of a few plugs to see the differences in how long that insulator might be.
 

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I've noticed a lot of places sell cold spark plugs for the ST and I was wondering what the difference is between those and the stock ones. Why I would want to put those plugs in my car?
With respect to the previous posters, here is the short version:

Plug too hot: detonation, knocking, pinging
Plug too cold: spark plug fouling
 

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"Fun Facts"

The difference between Hot & Cold for plugs is the length of the insulator between tip & contact with the metal "shell" of the plug.

Long insulator stays hot, because of the long path heat has to travel before reaching the colder wall of the shell.

For an extreme, some "Racing" plugs have an almost flat insulator at the tip - heat path straight to the wall to cool it as much as possible.

Peek inside the business ends of a few plugs to see the differences in how long that insulator might be.
Cut and Paste

http://e3sparkplugs.com/hot-spark-plugs-vs-cold-spark-plugs

Hot spark plugs feature a ceramic insulator designed with a smaller contact area surrounding the metal electrode to reduce heat transfer and keep the spark plug tip insulated. Cold spark plugs have a larger contact area and transfer more heat away from the spark plug tip. Because ceramic is such a poor conductor of heat, these spark plugs run cooler. Manufacturers specify a spark plug’s heat range using numbers but always ask before you buy as differing brands may use larger or smaller numbers to indicate a specific temperature range.

My pic



2 stage cooler on right
 

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^^^ Picture shows two different plugs, the one on the right has an extended tip and might not fit where the one on the left is required (piston/valves could hit the tip).

Looking down the inside of the plug is where the temperature difference can be seen. Hot will have a long insulator where a colder one will be relatively short (distance from tip to where the insulator touches the side).
 

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E3's explanation is the most convoluted way to say the same thing I did I've ever seen.

Look up an explanation from NGK, Bosch, Champion - whoever you like to see a diagram & pictures to explain it better.

The short path between the electrode tip & the plug shell (steel threaded part) of a short insulator gives the most cooling to the tip. A LONG insulator (as E3 mentioned obliquely) means the good insulation of that LONG path to the shell through the insulating porcelain will let the tip stay hot.

If you ever see a VERY cold racing plug, there's almost no porcelain 'tip' at all - an almost flat porcelain between the electrode & the shell.



If those plugs are used in the same engine, one is wrong for the application.

Extended tip works in a larger combustion chamber, the short "flat" one works where there isn't room for an extended tip. if you put an extended tip in an engine that needs a short one, the piston would smash it.

That recessed one would probably need to be a "hotter" plug to avoid fouling when used in the same engine. More likely to misfire if the engine designer wanted a plug that puts the spark further out. Extended tip style won't work when very 'cold" is needed, since the tip stands up beyond the base.

In either case, you can't tell heat range by looking at how long the tip is beyond the base - it's the distance from tip to where the porcelain touches the wall of the plug that counts.

Harder to explain this in words than pictures. The cylinder head is the "cold" part compared to the plug tip. The less insulation between the tip & the head the "colder" the tip will stay. The porcelain is the insulator (electrical & heat) between tip & plug shell, which screws into the head to transfer heat/electricity.

Touch an ice cube with a sheet of paper between it and your hand - feels cold right? That's heat transfer through a small insulator. Do the same using a phone book - virtually no heat transfer, just as there's little through a LONG spark plug insulator.
 

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Thinking those plugs are the same is a great starting point to blowing up one's next engine. While it may be true simply reducing all facts down to that extreme oversimplification is asking for it someday. The plug tip if it does not hit the piston can still be close enough to piston to overheat creating a localized hot spot and then run car a bit too hard and next thing you know you're looking at the melted hole in piston top. (and going WTF????)
 

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X2 sailor.

The E3 people are idiots. Read the last couple lines there, they refer you to STOCK plugs (owners' manual) and they (I assure you, I sold them) have no real provision for anything other than DEAD STOCK PLUGS. And this?...................

'Some spark plugs are made to burn hotter than others.'

Pure 'i failed school, especially physics class' bullshit. ALL plugs 'burn' at the same temperature, rather they RADIATE or DISSIPATE the heat off differently. The statement is flat 100% wrong. One controls combustion chamber temperatures by changing the heat radiation characteristics of the plug, NOT the temperature.

Physics for other idiots if you will.............their product is and always will be garbage. Like the old school Splitfires, the gimmick plug that first conned the masses into thinking $6 instead of $1 spark plugs were good and now all plug maker CEOs worship at the altar of Splitfire every day saying..................thank you for bumping our profits up 400%. All you people who buy into that stuff have been SCAMMED.
 

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Harder to explain this in words than pictures. The cylinder head is the "cold" part compared to the plug tip. The less insulation between the tip & the head the "colder" the tip will stay. The porcelain is the insulator (electrical & heat) between tip & plug shell, which screws into the head to transfer heat/electricity.

Touch an ice cube with a sheet of paper between it and your hand - feels cold right? That's heat transfer through a small insulator. Do the same using a phone book - virtually no heat transfer, just as there's little through a LONG spark plug insulator.
Thanks, sometimes crayons come in handy.[:)]

FWIW
Switched from NGK on left, to AC Delco on right. Did some nice hard hits will pull and inspect.

Prepping for a 10s run.
 

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Don't know what you're running them in, which style is stock for the engine?
 

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These are not for a ST so I don't want to post plug numbers and maybe confuse someone. The one on the right is the stock style.

To the OP
Heat range won't make it faster or slower .. a colder plug just helps control detonation at higher boost levels. To cold and you can get fouling. Gives you another variable to tune with.

For most people stock plugs and gap are all you need to know.
 
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