Spark Plugs - Which make a heat range?

[DOT2DOT]

Im gonna buy a set of colder grade plugs soon for my Uk R. At the minite she's using NGK PFR7B's which are standard heat range. Does this mean that they are heat range 7??? If they are 7, am I correct in thinking that I need 8's to go one grade cooler???
And final question, are the NGK iridiums ok or would Denso Iridiums be better. Im aiming for 300bhp. Cheers

 

[Fast Guy]

Yes that is heat range 7 and 8s are one stage colder than 7s for NGKs.

NGKs should be ok, I haven't heard of anyone having problems at that power level. I have NGK iridiums in at the moment and they seem OK.

 

[DOT2DOT]

Thanks pal