Well guys, my experience with GRP plugs have been very bad.... I have blown out about 3 plugs just trying to get my engine to tune right.
I have noticed that in my engines the spool up is faster with Novarossi rather than GRPs. And I have yet to blow out a Novarossi plug. And with the price comparison that I can buy 2 novarossi plugs for each GRP I really have looked the other way.