The R equals resistor, the N stands for 13/16 body in 3/4 inch reach, the 9 stands for the heat range and if it had a C after the 9 it would have a copper core center
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They where used in 340 and can be use in 426 hemi motors, they can't be used in any of the later after market BB aluminum heads like the Indys, B1 or eddy and 440 sourcedue to the machining around the spark plug hole, those heads need the RC type plugs like the RC9YC. Which is the same plug with the 5/8 body
The iron OEM BB heads use the J series plugs which are 1/2 inch reach with the 13/16 socket size body
It's hard to believe your telling mopar people how to decipher plug numbers. Old Champion charts are still around(ebay). Cab, how long have you been talking "plug numbers".. 50 years,60 years?
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I use Champion N6 to N10s on drag Hemis. R(resistor) doesn't mean a thing unless it has a radio.
I was taught to not use retracted gap plugs on any N/A gasoline motors where projected gap plugs would fit, I still do that
The coil or magneto knows exactly how much resistance it has to over come to fire the spark plugs, correct?
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Have you ever ran a MSD 7 series ignition box without using resistor spark plug wires with non resistor spark plugs?
If so how did that work out for you?
My first MSD 7 missed horribly until I got the resistor spark plug wires installed on my old NHRA stocker
The other MSD earlier 404 series race boxes didn't mind having solid core wires with non resistor spark plugs, ran good, lasted a long time
I should have read the instructions on the new MSD 7 race box first before using it
That mistake caused me to chase a intermittent miss between 5200 RPM to 5600 RPM for most of a year (8 NHRA races)
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I do now use retracted gap plugs on my E85 race motor with a MSD 7AL2 box and coil with resistor plug wires per many recommendations from many other E85 racers
To answer your question on my age I got the hot rod bug in 1963, I've had it bad ever since