As the title states I have a spark plug question. Yes I have done a forum search and yes I have found some very valuable information but none if it fit the niche I need so I'll ask.

First: What is the difference between a heat range 8 and/or 9 plug..ie which is the cooler running plug and what is the stock plug heat range?

Second: My target whp is 850+ (the stroker was installed over the weekend for those who follow my car). Which heat range plug should I be considereing from the HKS series? 50003-M45XL http://www.hksusa.com/products/?id=3115&rsku=6490 or 50003-M40XL http://www.hksusa.com/products/?id=3115&rsku=6489

I would appreciate any input, opinion, pro's, and cons on this one. Thanks all.

 

50003-M45XL

http://www.ngksparkplugs.com/tech_su...2.asp?mode=nml