AC Delco Spark Plugs

[Doug Meloan]

Needing to know factory correct spark plug for 1963 Cadillac.  I assume it is either the AC-44 or AC-45 spark plug with the green rings but can someone let me know if this is correct and if so which one?  Thanks, Doug

[Jason Edge]

Doug, It will be good to see you and the 63 in June!

[Doug Meloan]

Thank you for all the responses.  I ended up putting R45's in as they were readily available at the local NAPA store and fairly inexpensive.  Car is purring like a kitten so I will run them for a while and then pull them to check the burn color. Trying to get everything in top shape to hopefully avoid any issues when we drive it to the  CLC Grand National in June (1400 mile round trip). I have owned this car for nearly 25 years, but the furthest I have ever taken it was on a 500 mile round trip to Branson, MO about 8 years ago.  Still debating whether to drive our 1971 Coupe deVille or the1963 to the CLC, but really want to bring the 1963.   

[Tony and Ginny 429]

Do consider , learning to read the spark plugs in each cylinder of your engine
One of the --single best---ways to know how a cylinder and the engine is performing internally ,overall
The best plug for your car would be the one that burns a brown paper bag color, during your normal driving conditions
When they all burn that color ,you know all the cylinders are working as they should , the engine is very sound and the fuel mixture is correct( not rich or lean )
My plugs are doing just that,gotta love it
I choose to use the auto light 45 plug in my 64-429
This is fine tuning ,and not for everyone
You need to know all else about the engine is in perfect order ,before you play with plug heat ranges
I learned to like the auto light brand over all other plugs ,due to the durability they showed ,during my drag racing days in super stock
Autolight allowed me to make MORE passes on the track than any other brand available in the mid 60's before they required to be changed due to wear issues
Held the track record in that class , for 4 years ,with a Chevy 409 ,So autolights worked pretty good for me ---LOL !!!

[Jason Edge]

Doug, If you missed it be sure to check out John Washburn's Article on AC Spark Plugs in the Sept 2013 Self Starter.  I was trying to find another article he did on another subject and found that piece. Jason.

[Jason Edge]

If looking to stay original the R44 (resistor plug with part # 556 9993) was used with cars equipped with am/fm.

[William Cameron]

your post on spark plugs could be a good addition for "Help Topics" 

[David Thomas]

The AC 44 was the factory recommended plug for all around use. The 45 was an optional one step hotter and the 43 is optional one step cooler. You would use the hotter plug for low speed city driving IF there was a fouling issue with the standard plug, on the other end; you use the cooler plug for continuous high speed IF the standard plug ran too hot.