RE: {Chrysler 300} Spark Plugs in 413.

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.