Spark Plugs Cr8eix Or Cr9eix

[RUTHLESS]

WHICH PLUG IS EVERYONE RUNNING & WHY
I HAVE BEEN USING A NGK CR8EIX & NO PROBLEMS
I HEARD THE CR9EIX RUNS A LITTLE BETTER
ANYONE???

[GPracer2500]

I can't tell you what everyone is running and why they choose that. But I can tell you the difference between those two plugs.

The difference between a CR8EIX and a CR9EIX is the heat range of the plug. The 9 is a colder heat range plug. This has nothing to do with the spark produced. Plug heat ranges refer to the operating temperature of the plug itself. Plugs have to stay hot enough to burn off deposits but cold enough to keep from overheating themselves to failure (or causing other more detrimental problems--namely pre-ignition). Plugs control their operating temperature by varying the plug surface exposed to the combustion chamber and varying their ability to dissipate their heat into the head and cooling system.

http://www.totalmotorcycle.com/maintenance/photos/SparkPlugScale.gif

A plug's heat range has everything to do with the temperature of the plug itself and very little to do with changing the operating temperature of the engine (despite popular belief). This typically holds true unless maybe you get substantially outside of the manufactures suggested heat range. In other words, running a one step colder plug should have little to no impact on the engine's running temperature. Plugs just move heat from one place to another, they don't actually produce heat.

I'm almost sure 8 is the recommended heat range by Yamaha (I know this for sure for the 04', I imagine all years are the same). The only reason to run anything other than the recommended plug is if you have substantial engine modifications. Only in unusual circumstances would bolt-ons warrant a colder plug. Typically you'd need to be running a high compression piston and/or a combination of parts that allow the engine to produce significantly more power (heat!) than Yamaha intended. In those situations you'd need a colder plug because the stock heat range plug may be in danger of overheating.

Changing a plug's heat range won't add performance. Heat ranges are about matching the plug heat transfer characteristics to the engine's needs.