yellow_cad Posted June 21, 2012 Share Posted June 21, 2012 The 1954 Cadillac manual calls for the use of AC plugs marked 46-5. Someone had one on ebay so it is out there. I know the 4 is 14mm thread, 6 is the heat range, but don't know what the 5 would be. This is not S but is 5. Thanks for any input. Jim Link to comment Share on other sites More sharing options...
Guest Commodore Posted June 22, 2012 Share Posted June 22, 2012 The "-5" in the plug number indicated these plugs had a smooth porcelain insulator. Link to comment Share on other sites More sharing options...
yellow_cad Posted June 22, 2012 Author Share Posted June 22, 2012 The "-5" in the plug number indicated these plugs had a smooth porcelain insulator.Where exactly is the porcelain insulator smooth? Does this change the performance of the plugs in any way? Link to comment Share on other sites More sharing options...
D Yaros Posted June 22, 2012 Share Posted June 22, 2012 The white porcelain portion of the plug, running from the metal tip on top to the black base below would be smooth, instead of having grooves/rings. The only difference, I believe, would be in the fit of the spark plug wire; none in performance. Link to comment Share on other sites More sharing options...
Guest Commodore Posted June 22, 2012 Share Posted June 22, 2012 Here's a picture of an AC 46-5 plug on the left and 2 modern AC plugs. Link to comment Share on other sites More sharing options...
NTX5467 Posted June 23, 2012 Share Posted June 23, 2012 As I recall, the circumferential ridges near the top were added to make a longer surface distance for a spark to "leak to ground" at the plugs hex (nearest metal item when the plug is installed in the cylinder head). Plus give the spark plug boot a tighter "weather" seal, I suspect.Just some thoughts,NTX5467 Link to comment Share on other sites More sharing options...
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