champion rj18y spark plug

[fatecaptured]

When I got my Charger a few weeks ago I ran a compression test on the '71 440 hp that is in it. The compression readings I posted in another thread on here. As I was removing the plugs(maneuvering around the headers), I dropped one of the plugs and bent the end and chipped the porcelain around the electrode. I have almost a complete set of champions I took out of the coronet when I tore it down. I noticed the plugs are different. The plugs I took out of the Charger are RJ-18Y(champions) and the plugs I have from the other engine are RJ12YC (champions).

So my question is which one is correct? I know little about this engine in the charger other than I hasn't ran in a long time. Anyone got any ideas??

 

[coloradodave]

The 71 Charger 440 takes RJ12YC Champion plugs. The other plugs are a much hotter heat range. You wouldn't use these unless the motor was burning oil or running rich.

 

[fatecaptured]

Oh ok. That could be. It was down on compression pretty good when I tested it. Was going to just swap in the one I had dropped. But noticed that the ones i pulled out were different. Thanks.

 

[Stumper]

The 18s are quite hot. I would not run them. The 12 range is normal or standard for a relatively stock 440, and if needed maybe going up to a 14 range, but 18 is high.

 

[moparstuart]

so i have a six pack set up that runs really rich no matter what i do
can i run the 18's ok to compensate ??

 

[RustyRatRod]

I would correct the rich condition rather than compensate with plugs. It sure would make more power ultimately if you did.

Also, keep in mind, high performance engines generally respond better to a cold plug rather than a hot one.

 

[bigredbird]

Also, keep in mind, high performance engines generally respond better to a cold plug rather than a hot one.

Hey Rusty, I've got a crate 408 stroker that came with these plugs in it new, so I've been replacing each year with the same plugs. Can I go with something cooler, or is it better to stay with what the builders picked?

 

[RustyRatRod]

Hey Rusty, I've got a crate 408 stroker that came with these plugs in it new, so I've been replacing each year with the same plugs. Can I go with something cooler, or is it better to stay with what the builders picked?

What are the specs on the engine and what did they recommend? ...and did the plugs really need replacing? Plug technology has evolved. They generally last a while now if they are correct for the app.

 

[bigredbird]

ops: Wow, major dyslexia on my part! Make that C59YC racing plugs. (Guess that speed-reading class didn't work so well....)

Don't wanna derail this thread, so the short version on replacement is that because I store the car for 4-5 months (only 3 this year since summer hit in March), I pull the plugs and replace them with a shot of Lucas upper cylinder oil. Since they're out anyway and at least mildly burned, I throw in a new set when spring rolls around.