Okay after searching and reading up on NGK sprak plugs for the past hour and a half i have come to the point of slight confusion . My setup is a d15b7(stock) with a TD04L turbo at 7-8 psi. Now i wanna go either 1 or 2 steps colder....i have got the P/N ZFR6F-11(its stock gap but will regap to ~.33 or so) thats for one step colder. Now if i wanna go 2 steps colder i need to get a BKR7E? I guess after going through the P/N chart i am confused, will the BKR7E work fine on my car(thread and depth wise), are the BKR and ZFR interchangable ? Oh yea i am looking at the v-power line of plugs. Thanks for any help!