I voted CR8EIX, which is the equivalent to what I'm using on my 500. Stock for us is DR9EA, and I'm using the DR9EIX Iridium version of it. I used the IX plugs on my Vulcan, and they came standard on my Cobalt.
The smaller electrode results in a more focused and consistent spark. It also requires a stronger material, hence the exotic metals used in these (standard copper/nickel electrodes wear down more quickly, which would result in your tiny electrode completely disappearing before too long).
NGK 4218 CR8EIX IX Iridium Plug
Quote:
Originally designed to improve starting and reduce fouling on two-stroke engines, a Fine Wire electrode was found to improve performance in four-stroke engines as well.
A smaller electrode requires less voltage to jump the gap, resulting in fewer misfires, which translates to increased fuel economy and horsepower. A smaller electrode also reduces flame quenching.
Reducing the electrode size on a standard nickel plug would result in a drastically shortened life span, so the smaller electrodes require exotic metals such as platinum or iridium to maintain (and at times surpass) the longevity of a traditional spark plug.
While a traditional center electrode is 2.5mm in diameter, NGK's Iridium IX series features a 0.6mm center electrode.
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Note that the K plugs are made for specific engine designs that require a different type of plug, not as a performance upgrade. The difference of the plug gap area may or may not perform better for you (I have no personal experience to say either way). The extra electrode is added because that design tends to wear more quickly so they need a "backup" to avoid frequent plug changes.
NGK 3478 CR8EK Multi-Ground Plug
Quote:
Some engine designs require the spark plugs have the ground electrode placed to the side of the Center Electrode rather than below as on a traditional plug. This may be for combustion chamber design as in the case of a rotary engine, or a surface gap design as used in leaner air/fuel ratio’s on industrial engines.
The side electrode design tends to wear faster than a traditional plug. Erosion at these points creates a larger gap between the center and ground electrodes, causing plug misfire. Thus, if the engine design requires a side discharge plug, more ground electrodes extend plug life. Multi-Ground plugs are offered in 2, 3 and 4 ground electrode designs.
It is important to note that multi-ground does not mean multi-spark, there will still only be one spark at a time.
Caution should be made in selecting a "high performance" plug. If your car came OE with a multi-ground plug, your engine will likely wear through single electrode plugs, especially fine wire plugs, at a rapid rate.
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I got used to doing ignition tuneups on the Syclone (~$50 for wires, plus 6 spark plugs) seemingly every other week, so paying an extra $8 per tuneup on the Ninja to get Iridiums instead of standard plugs doesn't bother me. Even if I see no measurable performance improvement, they last longer and don't foul as easily, which means less time wrenching and more time riding.