AC 45S Odd Center Electrode

[Lawrence M.]

I found a set of AC 45S plugs I am going to use in my 1969 L46. The plug center electrodes are ribbed or grooved. The boxes are dated 10-70. Was the ribbed electrode something AC tried for a while that didn't work ? Should I use these plugs or find ones with conventional center electrodes ?

[Edward J.]

Re: AC 45S Odd Center Electrode

Larry, I have installed hundreds of vintage Delco plugs and do not remember ever seeing electrodes as you have, are you sure of the date ?? the flap has a 11 and a 12 could that be the date? at any rate I would not hesitate to use. I do not have the knowledge or remember the number of green rings on the porcelain surely that will help with dating the plugs Someone like Joe L. or Duke may know. Maybe the design of the electrodes helps with anti fooling, or Delco was running a trail period to see if they worked. when spark plugs are installed the electrode and tip always lands in different position maybe the design help fire each cylinder evenly in re-guards to heat. Just a guess.

[Lawrence M.]

Re: AC 45S Odd Center Electrode

Thanks for the reply Ed. Before I install them I just want to make sure somebody doesn't remember them as fouling like crazy. As for the package dates, from what I found in the archives the 4 thin green rings on the plugs ran from about 1960 to 1973-1974. The blue/white box graphics look like what I remember from the late 60's early 70's.

[Christopher B.]

Re: AC 45S Odd Center Electrode

Maybe these are the original version of the A/C Delco Rapid Fire plugs?? A lot of people think the rapid fire plugs are something recent but GM was selling them along time ago.

[Duke W.]

Re: AC 45S Odd Center Electrode

I have a vague recollection of that electrode design. The spark likes to propagate from a corner or edge. That's why center electrodes round off after thousands of miles. NGK plugs have a notch on the center electrode (V-power) and Denso has a "u-groove" ground electrode, and both offer more sharp edges than conventional designs.

I don't know why that AC design electrode was short lived. Your '69 was the first year that GM installed resistor plugs, but what you have is perfectly okay to use.

Duke

[Lawrence M.]

Re: AC 45S Odd Center Electrode

Duke,
Thanks for that information. Maybe the benefit of the design did not out weigh the cost. I have the non resistor rotor from K&B to go with the non resistor plugs.

[John S.]

Re: AC 45S Odd Center Electrode

I don't know why that AC design electrode was short lived. Your '69 was the first year that GM installed resistor plugs, but what you have is perfectly okay to use.

Duke[/QUOTE]
AC resistor plugs were used in 1955. A picture of the 55 plug was posted today. (note date on flap)

[Mark E.]

Re: AC 45S Odd Center Electrode

I also have a vague recollection of this plug design back in the day. No recollection of problems (which I would remember even with my memory), so probably ok to use.

It would be interesting to learn more about AC's intention and experience using this design.

[Timothy B.]

Re: AC 45S Odd Center Electrode

I have a used set of 44's that have those lines in the electrode, they are not that well defined but still good spark plugs.

It's got to have something to do with the hot spark jumping from a edge.

[Lawrence M.]

Re: AC 45S Odd Center Electrode

Doing a quick search through some of my old magazines I found these electrodes depicted in AC Delco ads from December 1966 and December 1967 in Hot Rod magazine. I found an ad on ebay that I could not date . The ebay ad looks like it may be earlier than December 1966. The "ribs" on the electrodes in the ads are always depicted as thinner and more numerous than those on the actual plugs.

[Jeff S.]

Re: AC 45S Odd Center Electrode

Larry

I have two boxes of NOS AC-45S plugs; those from the box with a '66' year code have 4 equal green rings, copper sealing washers, and, like yours, a grooved/ribbed center electrode.

Those from the box with '76-77-78' year code markings have 3 equal thin green rings, 1 thicker green top ring, plated steel sealing washers and a smooth, cylindrical center electrode.

Jeff

[Duke W.]

Re: AC 45S Odd Center Electrode

I have to laugh at their "hot tip" design. The only way to keep plugs from fouling is to run the proper heat range for the type of service, which is a function of the insulator design, of which most of the details are hidden under the steel shell. Grooves in the center electrode won't do squat. I think it was just a marketing gimmick.

Duke