RE: {Chrysler 300} Spark Plugs in 413.

Hey Dave,

I think that conversion chart might be comparing actual Champion plug series numbers, not the package numbers. In other words, for a RJ14YC, look at 14, a hotter plug, crosses to NGK XR4. 63 might be a C63 racing plug, a colder plug. So you can that the Champion 12 for J12YC (modern version of J10 YC) crosses to NGK XR5 that Noel posted as correct for his F. J10Y or J9Y, as used on the 300J, crosses to the R5670-6 in the racing line. Which is why I went to 7 to start with, one range colder. So the NGK 8’s would be 2 or 3 ranges colder than stock, should be more than enough, just make sure they don’t foul in normal driving, assuming you use your K for normal driving and not just drag racing 😊

Carl

From: D.C. Mason
Sent: Tuesday, December 13, 2022 8:41 PM
To: Carl
Cc: mgoodknight@xxxxxxxx; dplotkin@xxxxxxxxxxxxxxxxxxx; nicksgaragesd@xxxxxxxxx; chrysler-300-club-international@xxxxxxxxxxxxxxxx
Subject: Re: {Chrysler 300} Spark Plugs in 413.

Thanks Carl!

I’ll install the 8s and see how they do on the K (non-ram). (Adjusting the timing greatly reduced but did not eliminate the pre ignition). So, hoping to see an improvement 😄. If not we’ll give the 9s a go. We also almost exclusively run non ethanol fuel in all the old cars.

The chart came from this NGK site:

Heat Range Conversion Chart

ngk.com

As you say, I’m sure there are multiple variables. As I understand it, a cooler plug simply dissipates heat more quickly to the engine.

D&K

Sent from my iPhone

On Dec 13, 2022, at 9:05 PM, Carl <cbilter@xxxxxxxxx> wrote:

Hi Dave,

Champion 63 is an RJ14YC plug, which used to be RJ12Y or J12Y back in the day before Champion changed some of the numbers (sometime after 1965 but before 1980). They are specified for New Yorker or Imperial 413s, and even on those engines my experience has been you will likely get detonation given the 10.1:1 compression ratio and today’s gas. Depends on initial and total timing of course as well. Letter car 413s were specified to have plugs about 2 ranges colder. In the non-ram K a Champion J10Y was originally specified in the FSM which would be a J11Y or J12Y using the modern Champion numbers. And that was with 1964 hi-octane leaded gas.

That cross reference chart (published by Champion I think) might only be approximate; in other words, not exactly apples to apples. It was my understanding a modern Champion J12YC roughly crosses with Autolite 85 and NGK R5670-6 in the V power racing plugs as far as comparable heat ranges. Who knows. Use what works best. R5670-8 or 9 might be good, especially if you have ethanol gas. I run R5670-7 in the J currently with non-ethanol, but might try one range colder(8) next time. The special V tip helps.

Carl B.

From: D.C. Mason
Sent: Tuesday, December 13, 2022 6:16 PM
To: mgoodknight@xxxxxxxx
Cc: dplotkin@xxxxxxxxxxxxxxxxxxx; nicksgaragesd@xxxxxxxxx; cbilter@xxxxxxxxx; chrysler-300-club-international@xxxxxxxxxxxxxxxx
Subject: Re: {Chrysler 300} Spark Plugs in 413.

Apparently Champion 63s are called for in the 413. This crosses to the NGK R5670-8 (#3354) mentioned in a previous email (see attached chart). We have 63s in the K and still have slight pre ignition. I will try R5670-9 (3913) and see if the cooler plug helps.