Spark plugs recommended for aluminum Stage 2 street eliminators

I have been using the NGK FR-5 plug in my Stage1SE heads for as long as I have owned them (2006). Before that, I used the UR-5 in my iron heads. The UR-5 is the same plug with a tapered seat. Both plugs are projected nose plugs. In theory, they have a wider heat range.

https://www.vdlfuelsystems.com/anything-and-everything-you-want-to-know-about-spark-plugs/

"Projected Core Nose – places the spark an additional 1/8″ into the combustion chamber. Originally designed to prevent fouling by exposing the insulator/ center wire to the air fuel path and heat of the cylinder. In street applications it performs as a hotter plug at lower RPM while running cooler at higher RPM. This is due to the cooling effect of the fuel charge on the projected tip. In racing it does the same thing, however it has limitations because the core nose length and the long ground wire limit the ability to build the colder heat ranges in this configuration. If this plug could be built in a colder heat range it would be ideal for super-speedway use, but as it is its use is normally limited to short tracks, some road courses, and sometimes qualifying on the big tracks. Because it physically moves the ignition point it can more centrally locate the ignition which reduces combustion time. It can also place the ignition point in a more efficient location based on swirl. In some cases this plug has the same effect as increasing ignition timing."

 

First, higher numbers in NGK are cooler, not hotter. Second, hotter means the temperature of the plug tips. It has nothing to do with spark energy. Hotter plugs conduct combustion heat away from the spark plug tip SLOWER, so the tip runs hotter. Cooler plugs conduct heat away from the plug tip FASTER, so they run cooler.

https://www.ngk.com.au/technical_info/heat-range/

 

Depends on compression and ignition system. I use .045." You only have .008" leeway open or close from .039".

https://ngksparkplugs.com/en/resources/5-things-you-should-know-about-spark-plugs