Sparkplugs in a 400 cid

jimbo36 · Post by **jimbo36** » Sat Mar 28, 2009 10:39 pm

Just curious what plugs you are running in the 400 chryslers. The operating manual calls for XJ-10Y (Champion). Most people I talk to recommend 1 level hotter plugs with todays fuel. Any opinions? Jimbo36

gjrylands · Post by **gjrylands** » Sun Mar 29, 2009 9:37 am

I agree. You may even concider going to the XJ-12YC plug.

prowlersfish · Post by **prowlersfish** » Sun Mar 29, 2009 7:52 pm

the XJ-12YC covers a widder heat range being copper (C ) so should work fine

jimbo36 · Post by **jimbo36** » Wed Jul 15, 2009 12:54 pm

my local NAPA dosn't have a listing for XJ12YC Champion plugs. They even called the rep from Champion without success. They say the RJ14YC is the plug they list for my M400 Anyone shed some light on this. Thanks, Jimbo36.

LSP · Post by **LSP** » Wed Jul 15, 2009 4:07 pm

I believe the xj12y doesn't come with the c on the end.

jimbo36 · Post by **jimbo36** » Thu Jul 16, 2009 6:51 am

LSP Champion says it dosn't exist. What are you guys running in your 400 cid engines? Help! Jimbo

pwollsch · Post by **pwollsch** » Thu Jun 14, 2012 6:59 pm

Wish the conclusion was indicated..... Just did my twin M400's!!

I went by the manual....

Big D · Post by **Big D** » Thu Jun 14, 2012 10:02 pm

Jim, where are you getting that from? Everthing I have has RJ14YC as the correct Champion plug!
or NGK: XR5

hmc · Post by **hmc** » Fri Jun 15, 2012 2:54 pm

pwollsch wrote:Wish the conclusion was indicated..... Just did my twin M400's!!

I went by the manual....

and what did you use ???

hmc · Post by **hmc** » Sat Jun 16, 2012 3:58 pm

pwollsch

What number plug did you end up with ?

prowlersfish · Post by **prowlersfish** » Sun Jun 17, 2012 8:49 am

I come up with RJ14YC as the champion number for both the 400 and 440 . I have seen champion change the listings over the years . BTW the XJ10Y was replaced by the RJ12YC .

There is a easy look up on this site

http://championsparkplugs.com .

Of course there are other brands of plugs but champon was OEM on crlysler marine and seem to work the best on these .

Pwollsch you seemed conserned on what plugs you used bringing up a old thead what # and brand did you use ? I have a good data base and would be glad to help .

pwollsch · Post by **pwollsch** » Sun Jun 17, 2012 9:43 am

I used Champion RJ12YC. My Chrysler M400's have 1900-2000 hours, and I am trying to treat them delicately. I am satisfied with performance of plugs, just have read where some guys run hotter plugs, and I did not know the science behind it.

Big D · Post by **Big D** » Sun Jun 17, 2012 10:09 am

A plugs heat spec is is it's ability to dissipate heat from itself to the head. The proper heat range is a delicate balance; too high a heat range and the plug dissipates too much heat not allowing the tip to reach a temp that helps keep it clean, fouled plugs etc. Too low a heat range and it won't dissipate enough heat causing the end to burn up, and produce hot spots that could create a pre-ignition condition. The OEM heat range requirement is based on the engine design. After running for a season, a plug will tell you if you need to change the heat range providing the engine is properly tuned and mechanically sound, ie ignition, fuel delivery, compression, not burning excessive oil etc.

prowlersfish · Post by **prowlersfish** » Sun Jun 17, 2012 10:13 am

You will be fine with the RJ12YC . If you have issues with fouling then go to the RJ14YC . Being they are copper ( C ) they have a wider heat range .

Are you fresh or raw water cooled ?

prowlersfish · Post by **prowlersfish** » Sun Jun 17, 2012 10:24 am

Big D don't you have That backwards ? ( on the heat range )

a Quote
"The insulator material control the heat range. In the hotter heat-range spark plug, a longer insulator nose creates a longer heat flow path from the insulator tip to the threads and a smaller heat transfer area in the insulator, which allows heat to build up in the tip. "