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1998 deville, 2000 sls, 2006 CTS-V, 2001 STS, 2007 STS V8
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Discussion Starter #1
does anyone know the heat range for the two plugs for the sevilles(and other models)....41-987 and 41-950......the 950's are for 1999 and below and the 987's are for 2000 and up..so , what changed? ..i think its the heat range. but im not sure , anyone have any idea?...I am asking this because i bought some 41-950s from auto zone because they didnt carry the 987's..and i am using them in my 2000 seville. everything seems to run fine. i just want to make sure.
 

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White Diamond '03 DHS (with DTS floor shift)
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2000 is when Cadillac went to COP ignition and slightly lower compression ratio. I suspect it has something to do with that but beyond that I do not know. This link may be of limited help (note the bottom paragraph). You could also use the "contact us" button to ask A/C Delco the question. Post back if you do, inquiring minds want to know.
http://www.acdelco.com/html/pi_plugs_ident.htm
 

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Ranger said:
2000 is when Cadillac went to COP ignition and slightly lower compression ratio. I suspect it has something to do with that but beyond that I do not know. This link may be of limited help (note the bottom paragraph). You could also use the "contact us" button to ask A/C Delco the question. Post back if you do, inquiring minds want to know.
http://www.acdelco.com/html/pi_plugs_ident.htm
"In the early 1990s an all numeric identification code was developed to ensure that the proper spark plug would be selected for replacement in specific engine applications. The numeric code does not in any way correspond to the heat range of the spark plug. Therefore, selection of a spark plug with a different code number is not recommended. The heat ranges may be drastically different between two different plugs and engine damage or poor performance may result."

If I had to guess, I'd say the 2000 model has hotter plugs as a result of the lower compression, redesigned combustion chambers, and 87 octane.
 
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