Spark Plug Heat range
Yeah like N96 or RN9Y
R means resistor, N is for the long reach threads (3/4") as opposed to a 440 that uses J (3/8" reach) The numeral is the heat range and Y is extended tip
I think YC would be extended tip copper, no idea what some of the newer stuff is, or the "mini" plugs
I used to run 9's in my 10.5 (advertised) 71 340
