W2 408 Dyno results today !

Test, test, test. I will not make a recommendation. But instead of typing it all out I’ll paste this from Mike Canter on dragstuff.com

Spark Plug Heat Range
If you keep on adding timing until your finish MPH falls off but you still have no color on the plug’s ground strap but the porcelain has good color then your plug is too cold.

If you have lots of color on the ground strap but the porcelain is clean and white then the plug heat range is too hot. The heat from the plug is cleaning of the fuel ring from the porcelain.