1970 340 SPARK PLUG RECOMMENDATIONS

brian6pac said

N9Y or Autolite 63 worked for me, I got more mileage out of the Autolite's.

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I couldn't get Champions to last on my '69 Swinger 340 back then. I always had good luck with Autolites performance and lifetime. Of course, back then I changed plugs a minimum of twice a year.