Spark Plugs for NB

Technical Area Engine, Transmission, Exhaust etc
1

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  1. My model of MX-5 is: NB 1.6
  2. I’m looking for technical help or recommendations on: Spark plugs.
    I’ve just renewed the spark plugs on my non-turbo, non-vvt 1.6 NB. The old ones are NGK BKR6E-11. They appear very old and corroded around the body, but the important end is a perfect colour - light tan, no oiling. The engine ran perfectly with them. I was advised to fit BKR5E-11. No discernible change in performance. Elsewhere, I see the old plug number recommended - the BKR6E-11. I’m wondering if I have fitted too hot a plug. I haven’t yet checked the colour, but will do so.
    Any thoughts, please. _