I understand that factory is the 4-prong NGK 3199 (BKR6EQUP).

I have recently used Iridium BKR6EIX in my 2006 X5 3.0i 6spMT and like it.
I wrote a DIY here...

DIY: 2006 X5 3.0i Spark Plugs using NGK Iridium BKR6EIX

https://xoutpost.com/bmw-sav-forums/...m-bkr6eix.html


I just wonder what everyone is using out there for your E83...

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT