Just wanted to know what you guys were using plug wise for a stock 70 340. Champion N-12Y came out of it but my book shows N-9Y for 69-72 340 N-12Y was not used until 1973.
Spark plug selection
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7e5hangten360
semi-pro
use rn9yc champions. that would be correct for a 68-71 340 application. if you use aluminum heads, edelbrock recommends rn12yc.
Thanks for your comment. Champion web site even said to go with RN12YC. My old dealer catalog spec. N-9Y. Searches were not conclusive either.
I would use 10's and run them and take a look. 9's are pretty cold. 12's are hot and used with electronic ignition. I would check out a few more applications and see what's up.
Rat Bastid
Dunamis Metron
Use the “C“ series rather than the “N” series. Better plug.
7e5hangten360
semi-pro
the only difference between the champions c series plug and the n series , is the socket size required to install them. so, yes you could use a rc9yc plug instead of a rn9yc. i have used the champion rn9yc plugs in my 340`s since the 1980`s. i even still used them in my 360`s with cast iron heads. when i switched to edelbrock heads, i used the recommended rn12yc plugs as per edelbrock instructions. the 340`s from 1968-71 came from the factory with rn9yc champion plugs. if they were good back-then, they should still be. i understand that this was for street use.
Those smaller based plugs could come in handy if you are having header clearance issues.
Back in the day I tried them all on my stock 69 340. Every thing but 9’s ran like ****.
lemondana
BlackDart
I used to run N6Y and N7Y's in my 68 340 back in the 70's-Don't ask me why, I just did.
My Motors Manual specifies J12Y Champion plugs for 1962 & later, long before elec ign came along.
A lot of engines would be running better if they used the hotter spark plug that the factory specified.
A lot of engines would be running better if they used the hotter spark plug that the factory specified.
Dan the man
Well-Known Member
I run NGK plugs in all of my yard equipment even though they might call for champion plugs, they start better, perform better. When I had my '73 dart swinger with a 318 I ran Bosch mostly. My parents bought a new 5th Avenue and it ran rough at a idle, my dad had the dealership install Bosch platinum plugs and the rough idle went away. I'm not saying that champion plugs are junk, it's that I've never had any luck with them.
QuickDart360
Well-Known Member
How did these colder plugs perform? Any fouling? Thank you.
Thanks everyone for their input. Good information. Just want to get this build completed. Need to make an engine run stand out of my engine cradle so need to move forward. Will go with the N-9YC. Have factory manifolds so install with either size plug should not be an issue.
7e5hangten360
semi-pro
for what i remember, the j series spark-plugs from champion are for big-blocks.
lemondana
BlackDart
I remember the 340 ran hard, but the plugs only lasted 5-6000 miles. But they were cheap and everywhere, and it seemed no one else used these two numbers. Used to get them from Farm stores, Wheelers, Tractor Supply and such. Most of them were 99 cents a piece.
lemondana
BlackDart
Sorry: I forgot the quote for above.
Rat Bastid
Dunamis Metron
They are designed to only last 5-6k.
Swinger 340
Well-Known Member
I have and still do use the N-9y plugs (when I can find them) in my 69-70, 340's. The "R" are for the radio interference and the "C" is for copper. I have heard that the resister "R" plugs, fail often. I run copper spark plug wires and copper dist. caps , so why not use "C" (copper) plugs. They work well for me. The last plug change I did had over 60,000 miles on them. Setting the gaps correctly are important, as well as the points. Always install a new condenser when changing the points, it prolongs the points.
Thanks for your comments. Went with the copper variety of the N9Y. Did not get the resistor plug for my radio does not work.
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