What are you people using for spark plugs in a 71 340 call for N-9-Y ?
Closest Napa list in a Champion is N-12-Y are they not too hot ,car is stock street car.

i use them in mine...street cars need a hotter plug... i say use em

Try a Champion RN9YC or a RC9YC
The R indicates a resistor and the N or C indicates the spark plug body style, N are 13/16 socket size with 3/4 inch reach with a protruded gap and the C plugs are the same accept the body are 5/8 inch socket size
If you can get Autolites try either their 3922 or 3924 in the 5/8 body size

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