I find myself frequently confused about spark plugs.  In short, I have no life....

Soo.....  I want to figure out what the difference heat range really implies. 

While ordering plugs for my S2R1K I noted that the NGK DCPR8E is specified, so I ordered the DCPR8EIX (iridium) which is not specified. 

But why not the DCPR9EIX, why not the DCPR7EIX?  Which one's hotter?  Which is colder?  What the fak does colder and hotter really mean!?

Also, I searched, "Spark Plugs" and much to my chagrine, there wasn't already a "Spark Plug" thread...  How could this be?  Why aren't threads named specifically in accordance to what they embody!? 

Also, what sizes according to make fit?

So help me out here folks, If you can explain heat range, that'd be swell, and if you can explain why it'd matter when choosing replacement plugs, that'd be nice too...


Here's the little that I know.

I chose iridium because they are less prone to wear, and they come to temperature faster, a must for a/c bikes.  and because I couldn't find the equivelent Pulstar Plug, which is what I really wanted to try from the get go.
 
On the M900 and the S2R1K, the DCPR8E is specified, which means these two motors at least share...
12mm Thread, 19mm (3/4") Reach, 5/8" (16mm) Hex Size, Gasket Seat, Resistor, Removable Terminal, Projected Tip, .027" (0.7mm) Gap

On the Denso front, there are plugs, and then there are racing plugs!

the Denso iridium plugs are,
IXU01-24  for $35
and for us poor iridium buyers
IXU24 for $12

the heat range just means how hot the plug itself gets. in reality, its heat retention. a hot plug retains more heat near teh surface of the plug, and a colder plug retains less heat near the surface of the plug.

My carbed 900 +944 hi comp piston kit would run much better with a 7 than an 8. while my stock S2R1000 runs like shit with 7s and perfers 8s.

I personally woudlnt recommend spending the extra dough on iridium because the cost vs performance (the performance you can notice atleast) isnt worth it. a regular NGK plug is about 3 bucks while Iridiums run 3x that cost.

in the case of a dual spark buyer, thats a lot of dough in plugs. an yes while your plug does last longer, the plug degrades over time. so a brand new standard plug every 6,000 miles sure beats 1 iridium at 12,000 miles (thats how i see it atleast, its not a fact so dont go by it)

The 9's are colder, meaning the center electrode is shorter, so it will actually run cooler.
7's are hotter.

8's are what you need.

I think the NGK website will explain the sizing and other details:

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

A plug that is too hot can cause detonation and engine damage.  When I say too hot I mean a plug that is blistering and shoes signs of electrode wear and melting, or worse, cracked porcelain, not the whitish, clean plugs you are seeing in the closed loop bikes.  Too cold and your plugs will foul, causing misfire and no start. 

In that case I wonder if going to 9's on my wife's Duc will help with its rich situation?

Personally, I don't mind spending the coin on iridium plugs as that still makes it the cheapest maintanence part I have to purchase, and likely I'll replace them at 12K with the belts, which will be painfully more and not show any wear at all.  This Ducati priced stuff gives me heart burn.

Here's the thing, I've heard heat range numbers on NGK versus Denso are the opposite.  Now I'm not sure this is true, but that would mean Denso 9's are cooler and 6's are hotter...

I was fouling plugs regularly on the Monster, and went to one step hotter to an DCPR7E & the problem went away. But I'm at 5,200 feet in elevation so it runs rich, but go down to 2,000 feet or so regularly enough that I don't want to re-jet the carb for the altitude. One step hotter plugs seem to be a good compromise.

Pages and pages of good info on the NGK site at:
http://www.ngksparkplugs.com/tech_support/spark_plugs/index.asp?mode=nml