Spark plug heat range?

[OldSchoolin86]

Why would someone that heavily modded a motor put a colder plug in it? What would be the most important reason? Here's what the motor basicaly is:

Air cooled 4-stroke
big bore
12:1 compression
race cammed
bigger carb(tuned for max performance)
free flowing exhaust
slight timing advance
rev box

Any ideas? ;)

[83200e]

Keeping the plug tip from overheating.All the mods you mentioned would probably let the combustion chamber get to hot without going to a colder plug.

[MTS]

so it dosnt heat the plug up and melt it :P with all that compresion :)

[ATC crazy]

I recently put an exhaust and air filter on my fourwheeler and I haven't rejetted it yet (it didnt recommend a jetting change) but it is running a little hotter (lean) than it did when it was stock. Im going to try a colder plug in it next time to see if it will cool it down a bit.

[OldSchoolin86]

Anybody else want to stab at this one?

[jenndnn3]

Preignition

[OldSchoolin86]

Well, usualy when you put a question out like this half the answers are completely off the wall. I have to say that I'm pretty impressed with the responces. Good job everyone! A couple of month ago I read a tech article from NGK about this. I have to admit, my view on plugs was a little off. It was really cool to learn the science of tip temps and why you would use different heat ranges.

If you would like to learn more about spark plugs and thier heat ranges, here is the link to the NGK tech report. I highly recomend it to anyone that want's to know more about engine building and tuning.

http://www.ngksparkplugs.com/techinfo/spark_plugs/techtips.asp?nav=31000&country=US

[MTS]

Wow that was a good read Oldschoolin86, thanks that inlightend me alot about spark plugs :)

[Wickedfinger]

That was really good Oldy ..... I am a little amazed with the spelling/grammar errors though on this professional document!.