Spark plugs

[Jacksboys]

I use to feel like I knew cars and engines pretty well until a co-worker talked to me this past week.  He has a turbocharged honda, which he likes to experiment with and he asked me:

"What does it mean to go to a colder or hotter spark plug?"

Well, I was stumped because I have always gone with the recommended brand or type and never had a problem.
Can someone describe to me in detail the difference in hotter or colder spark plugs along with how to tell the difference when at the store.
Thanks

[duodec]

Colder plugs transfer heat away from the center insulator/electrode faster than hotter plugs, and as a result tend to be cooler in operation.  Hotter plugs have less material connecting the center insulator/electrode to the shell (usually a deeper or wider air gap on the business end, though possibly different formulations of insulator) so heat transfer to the surrounding head material is reduced.

Thats why the old old advice to run hotter plugs in a car that has started to burn oil exists; the hotter plug would tend to burn off the oil better than a cooler one, so not foul as quickly.  Sometimes going with a cooler plug, especially in higher compression scenarios, can reduce the tendency towards detonation or allow use of a couple more degrees of advance without detonation.

[Bullitt-]

heard that too hot a plug can "burn pistons" ?

[duodec]

heard that too hot a plug can "burn pistons" ?

Detonation can blow a hole in a piston, or break ring lands, or cause other damage.  Not sure if there's another avenue for damage from a hotter plug.

[Jacksboys]

Colder plugs transfer heat away from the center insulator/electrode faster than hotter plugs, and as a result tend to be cooler in operation.  Hotter plugs have less material connecting the center insulator/electrode to the shell (usually a deeper or wider air gap on the business end, though possibly different formulations of insulator) so heat transfer to the surrounding head material is reduced.

Thats why the old old advice to run hotter plugs in a car that has started to burn oil exists; the hotter plug would tend to burn off the oil better than a cooler one, so not foul as quickly.  Sometimes going with a cooler plug, especially in higher compression scenarios, can reduce the tendency towards detonation or allow use of a couple more degrees of advance without detonation.

Thanks duodec.
But is there a common way to tell which are colder and which are hotter by just looking at the numbers or something on the packaging?
Thanks.

[Bullitt-]

found this
http://www.championsparkplugs.com/sparkplug411.asp
 look at bottom left "Manufacturer's Numbering System"

[OUTLAW]

simple rule of thumb is the higher the number the hotter the plug...n-9y is cooler than a n-12y.
another thing about hotter/cooler plugs I read says that the hotter plug produced a higher Kv spark and traveled faster from electrode to ground and a colder plug traveled slower which in a race motor is the equivilent to a long duration flame front on todays engines (longer spark life time) but when you are talking nano seconds ....who knows

[Jacksboys]

Thanks for the info.  That is just what I was looking for.    
Now I feel a little more educated. 

[Grancoupe]

Here's a site with alot of info
http://www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp?nav=31000&country=US

[matt63]

You can't compare the heat numbers from one spark plug mfg to another.  Also, I believe that American plugs have lower numbers for colder plugs and European plugs go the other way.

[matt63]

You can't compare the heat numbers from one spark plug mfg to another.  Also, I believe that American plugs have lower numbers for colder plugs and European plugs go the other way.

I mean Japanese not European.

[Jacksboys]

Here's a site with alot of info
http://www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp?nav=31000&country=US

Thanks

[Grancoupe]

You can't compare the heat numbers from one spark plug mfg to another.  Also, I believe that American plugs have lower numbers for colder plugs and European plugs go the other way.
[/quote
I think the temp #'s are relative to the plug manufacturer. Granted one company may go up while the other goes down as far as heat/#'s. However colder is colder and hotter is hotter. That still remains the same regardless of what contry your in. So if you want a specific temp plug you just go accordingly to the manufacturer. What i mean is, if you want a colder plug in NGK you may have to go up in numbers while a colder plug for Autolite you may have to go down. I dont think the #'s is what is important. Its the temp and that's gonna be the same for any manufacturer.

[Grancoupe]

No problem jacksboys.