Spark plugs which type?

[toolmanmike]

Isnt the n9y the stock plug for a 340? If so s n14y is hotter, not colder if my pornographic memory serves correctly.

I'm running Autolite 3923s, one step colder in my 318.

Watch out with colder plugs. I converted the stock Champion number to a Autolite and got a step colder plug. I fought a dirty idle issue for a long time before I switched to a warmer Champion. Within minutes, the idle cleaned up and those plugs have been in ever since. I don't trust the conversion charts.

 

[RJRENTON]

My opinion....
The std 318 2bbl came with Champion N14Y. After l installed 4bbl, 273 Hp cam and manifold and recurved the Prestolite dual point distributor, i switched to Champion N12Y. After rejetting the carb and a little quicker advance, l changed to Champion N11Y.
Depending on your specific conditions, you may want to consider N10Y (std hemi plug).
Ethanol blended fuels, depending on the ethanol percentage, may require significant richer jetting, because the higher percentage of ethanol in the composition will result a cooler burning condition that MAY need a slightly warmer plug. Its better to start out with a colder plug than to damage the engine. Which brand of plug to use is up to you.....the NGK boys have their favorites, the same is true for Autolite, Bosch, E3, AC, etc..... I have found NOS Mopar on line as well as the other brands.
Just my opinion of course.

 

[Slap Stick]

In 73 the stock plug for the 318 was N13Y.
With ethanol fuels you increase jetting because 1)ethanol has a lower energy content and 2)ethanol is an oxygenate, leaning the mixture.

 

[ODZKing]

Maybe we could do up a spark plug chart like in an Excel. Engine, original plug suggested, suggested replacement one hotter, one colder etc. I think Dave would post that is the help section.