Modern fuels and location around the globe have different blends and require a different approach ie E5 fuel and E15 fuel Modern fuel burns a lot faster than the good old stuff in the 70's so it will need a hotter spark plug to ignite it, consequently ignition timing needs to be adjusted dependant on the fuel you use. BP6 is the lowest i would go but your fuel and location on the globe may need a different approach.
Don't North America cars also have different timing, which if I understand correctly impacts heat of the plug? I ordered some BPR6EIX since my non-iridium plugs were a 6 and have been ok. Will go from there.
Do you have a reference to share for this? I can agree that if you are using a standard electrode ES NGK plug of heat range "X" with good results, then using a colder VX or IX electrode NGK plug of heat range "X+1" would probably give good results, too (as the smaller center electrode of the VX and IX plugs, for the same heat range number, run hotter which is what gives them the better resistance to fouling), but that really isn't the same as saying NGK uses different heat range numbers for the different electrode designs.
Installed my iridium plugs, but I can't figure out how to use them. The have solid terminals but the extensions (I just replaced) are designed to work with threaded terminals. How are you making this work?
The top "normal" metal terminal (used to?) unscrew from the NGK IX plugs leaving the threaded rod terminal needed for Ferrari: Image Unavailable, Please Login I hope that hasn't changed, or did you buy a different brand? Also, I see a lot of links about counterfeit NGK plugs lately...
I just realized there are two models of BPR6EIX made by NGK. 6637 with the screw off end and 3903 with the solid end that can't be screwed off. Turns out I ended up with 4 of each
I don't see any reference to 3903 or 6637 here? https://www.oreillyauto.com/detail/c/iridium-ix/ignition---tune-up/spark-plug/b14eb31b13d7/ngk-iridium-ix-plug-number-bpr7eix-spark-plug/ngk4/4055 Where are you seeing those numbers? Looking to order some for my GT4. Imagine these are the correct ones?
I went with the 6 heat rating so the product numbers are different, but I think the one you are looking at is right because the electrical terminal is listed as "removable nut" so you should be able to screw off the terminal.
Been the case for a decade or more... Factory oem appearing Honda, Toyota parts...everything is ripped off out of China and now Eastern Europe...