Which plugs?!?

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Larsen74Dart

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so much information and so little patience...
I've been searching threads and cannot find anything concrete.
Which plugs are original or which plugs would be best for my 1974 318 Dart?
I pulled a plug to check and it's an NGK GR4GP. Tried to cross-ref, but RN14YC "may not fit your Dart" isn't comforting.
From all the charts, manuals, I've found, best I can tell is I either need RN12YC, RN13YC or RN14YC. All are either listed as "OEM" or "recommended".
What say you??
 
Back in the day, we used to sell RN 12Y Champions to anyone with a 318. The R means resister and the C means copper electrode, but I don't recall a C on anything we sold.
 
RN12YC was my go-to (404 by my memory??) lol. I like a RC12YC these days as well. Same plug but smaller socket. better with headers.. LOL
Many of the later 70's and into the 80's listed RN14YC.
 
Larsen74Dart said:
Why 14 and not 12? I know it has something to do with the "hot", but not sure how they differ. Trying to learn something new today so I can go fishing...
Click to expand...
Use a 12 then. Use a 9. It's not my car. I recommended a 14. They or their crosses are generally in stock everywhere. Normally, the 12 and its crosses have to be ordered. I always use 14 or equivalent because they are readily available.
 
If you want to be a complete pervert about it and gain yourself a small but real improvement in driveability/performance and fuel economy, take a page out of a book written by AMC and copied by Chrysler and install a set of NGK ZFR5N plugs, stock № 3459. They have extended-projected electrodes to move the spark away from the quenchout zone, so the fire gets lit more dependably despite a charge that's stratified or a little too rich or a little too lean. The electrodes won't get hit by anything on a stock or near-stock 318, and these plugs are the correct heat range, and their build quality is a whole hell of a lot better than Champion.
 
To be clear, I never recommended any plug. I simply gave a part number to cross from. Champions have been slipping for a long time. I used to run them all the time, now I run NGK or Autolite. I'm familiar with the Champion numbers, so those are the numbers I throw out.
 
The GR4 or J14 is the plug you want to use in a low comp 318 with today's fuel.
Just about everyone running on pump gas is using too cold of a plug.
 

Professor Fate said:
Autolite 66. My go-to.
:)
Click to expand...
Wow, the PO of my Swinger screwed in a set of Autolites and I had a hell of a time getting them unscrewed. Like the threads were a different size. Thery were probably too long and had carbon on the last few threads. :BangHead::BangHead::BangHead:
 
slantsixdan said:
If you want to be a complete pervert about it and gain yourself a small but real improvement in driveability/performance and fuel economy, take a page out of a book written by AMC and copied by Chrysler and install a set of NGK ZFR5N plugs, stock № 3459. They have extended-projected electrodes to move the spark away from the quenchout zone, so the fire gets lit more dependably despite a charge that's stratified or a little too rich or a little too lean. The electrodes won't get hit by anything on a stock or near-stock 318, and these plugs are the correct heat range, and their build quality is a whole hell of a lot better than Champion.
Click to expand...

Have you ever measured the resistance in the NGK plugs?

I believe that the "R" in any resistor plug should be 5 k ohms. And it's a known fact that you can't measure the resistance of Champion resistor plugs using a basic volt/ohm meter (but you can for other plugs). It's also a known fact that resistance can or does change as plugs age. A plug that is burning different than others (different color) might be because it's resistance has changed.

I would think that choosing the "best" plug in any situation (aside from heat-range considerations) might also include if your plug wires are of "modern" construction (with a resistance of 5k or more ohms per foot) or legacy / original factory resistance (500 ohms per foot).

Does anyone here with a non-hei ignition system know or pay attention to your plug wire resistance?
 
Oldmanmopar said:
n12's for 318 2bbl n9's for a 340 I put 12's in a 340 and it ran like ****, going hotter is not the ticket
Click to expand...
Boy I wonder if higher cylinder pressure didn't have something to do with a 340 running poorly with a hotter plug.
Fact is engines with lower cylinder pressure will benefit from a hotter plug.
 
67CBodyGuy said:
Have you ever measured the resistance in the NGK plugs?
Click to expand...

No. It's specified as 5kΩ, and in the ~3 decades I've been running these plugs in a variety of Mopar engines (2.2/2.5 4-cylinders, Slant-6s, 318s), with a variety of ignition systems (points, factory reluctance electronic, factory Hall-effect electronic, HEI, MSD…) and a variety of plug wires (stock, Magnecor, Aurora, parts-store replacement…) I've never encountered any problems, issues, or weird stains on my socks that could be related to the resistance of the spark plugs.
 
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