i am running a BR8ES right now but i have heard that running a hotter plug helps a lot my mods are:

New top and bottom end
wiseco piston
two base gaskets for raised port timing
CR250 head gasket more more compression
LRD unlimited CDI
fmf pipe and silenver
K & N filter with outerwears
36mm Keihin PJ flatslide carb

 

If you raise compression by milling the head or installing a "high compression piston", install a "high performance camshaft", or make engine modifications that increase volumetric efficiency that in turn increases combustion pressures that again in turn increase combustion temperatures, you need a colder spark plug. Heat ranges refer to the temperature that the spark plug itself maintains during engine operation. The center electrode and porcelain that are inside the combustion chamber may reach temperatures as high as 1600 degrees F. Combustion temperatures (the actual flame itself) will reach over 2500 degrees (NOx is produced around 2300 degrees). If you run a "hotter" spark plug it will physically run hotter than it should which may cause detonation (premature ignition) and cause serious engine damage. So what you need with engine modifications is a spark plug that is "colder" because it will dissipate more heat to the cylinder head and physically run "colder". That is the claim to "copper core" is that they will transfer more heat a faster rate under load and maintain a constant temperature while normal driving, providing a greater "variable thermal capacity".

Check with the spark plug manufacture to make sure of their numbering system. Some manufactures heat ranges increase with numeric increase, and some decrease. The porcelain of the plug should be close to white with a tan tint to it, all white you should drop to a colder plug. If it looks to be collecting oil deposits, run a hotter plug. If it is black and sooty, check for too big of a main metering jet or possibly a choke or float problem.

Just for your information, in the average vehicle at wide open throttle, the heat causes the spark plug gap to increase up to .05" from the ground electode bending due to the heat increase. Theres a piece of useful information.

Good luck with your mods.

 

Yeah! what specta said. Be VERY careful running hotter plug on a high perf two stroke, the penalty for going too hot is a holed piston, or other forms of abnormal combustion.