Spark Plugs

[Mike Cobine]

This is a two-parter:

1. With the disappearance of the AC 44 spark plug from the stores, what are you using for actually driving your Corvettes now? Most stores want to substitute the R43 and some want to use the R45S. Where the 44 was originally recommended, the 45 was for City driving (hotter plug to prevent fouling) and the 43 was for Highway driving (cooler plug for extended operation). So I'd think the R45S would be fine for around-town cruising but might need changing before one of those road tours. The R43 would be fine for the touring, but foul out too quickly for Saturday night cruising. Does the Rapidfire have one that is a closer match?

Is the unlead gas of today that much different in heat from the leaded gas of then that the colder plug works best?

Thoughts?

2. From a show perspective, many are selling NOS plugs for showing the cars. Naturally, these cost. However, many have four thin green stripes and many have three thin and one thick green stripe. Which are correct for which years?

Thanks,
Mike

[William C.]

Re: Spark Plugs

Mike, the 4 equal ring design was proper for cars up thru the mid-70's I have a set of "Acniter's" 3 small 0ne large band dated early 81, so the change was before then.

[Duke W.]

Re: Spark Plugs

Chevrolet's heat range recommendations were on the cold side. The AC 44 was subject to excessive fouling in normal driving. The AC 45 was just right for normal street and highway driving. The AC 43 was too cold for any kind of driving other than race track hot lapping.

Since AC no longer offers non-resistor plugs, I recommend the NGK B4 or Denso W14-U. These are non-resistor plugs approximately the same heat range as the AC 45, and like the 45s they do not have an extended tip.

Modern fuels have nothing to do with plug heat range. Proper heat range selection is a function of the average engine load, and hot lapping race tracks requires a colder plug than street and highway driving. Modern fuels should result in longer plug life because unleaded fuels do not form lead oxide deposits on plug insulators.

Duke

[Jeffrey S.]

Re: Spark Plugs

Mike
When Delco first came out with "Hot Tip" spark plugs (the first ones with the "ridges") they had no green bands. They were first produced in about 1956. Previous to this the upper porcelain was plain (straight- no ridges) and the numbers were 43-5, 44-5, 46-5, etc. They also may have had the designatio "Corolox" until about 1955. The first Crovette to use the "Hot Tip" was the '56. In 1960, the "Fire Ring" designation was first used and the 4 thin green rings appeared. This was used until 1973 or so, when the upper ridge was fattened and the green ring on this boss was widened. This was used until the 90's when the rings were removed but the upper boss remained wide. Do not confuse these plain plugs with the '56-'59 plain plugs. These are also made in Mexico. All plugs up to the mid 80's or so were either made in the USA or in England. I have some AC44's that were made there.
As far as the heat range is concerned, unless you plan to race your car, a 4 or 5 heat range would be just fine. I use AC44's in my '69 300 hp car and I don't push it and have not had any fouling problems. This season I intend to use an AC45 and see if I don't get any pinging. (If the plug is too hot for the engine pinging will occur until the timing is retarded which would cost power.)The currntly available AC R45S (5 heat range, extended tip) is a good plug for most small block Corvettes.
I hope this helps.
Jeff Salz

[Dave S.]

Re: Spark Plugs

Jeff,
In addition to all the good information you stated, AC made plugs in the late 50's up to possibly 1960 that were straight number (44, 45, 46) that had the 4 equal ridges but they were not green, unlike the Corolox plugs which were smooth. They did have a green AC logo on them. I believe the green rings started around 1960.

[george romano]

Re: Spark Plugs

For a good all around spark plug that will last on the street, hiway, and dragstrip, buy the Autolite equivalent of the AC44. They will last for years. I have Autolite in all my cars and trucks, and I love them. the current set that is in my Dodge truck has been in there since 1997, and there is 74000 miles on them.

George

[Jeffrey S.]

Re: Spark Plugs

Dave
You are right and that's what I meant about the Hot Tip plugs dating from 1956-1959 with plain ridges. You are also right that 1960 was the beginning of the green rings. This info can be verified by studying ads for AC sparkplugs from this era. They are all dated with pictures of the plugs. I have seen ads from every year starting in 1953 and contiuing into the 90's.
Jeff

[Dave S.]

Re: Spark Plugs

Jeff,
My information comes from the original boxes of plugs themselves. As you know they are dated and by studying the various boxes and their respective dates you can see the changes. Interesting stuff.

[John Thomas]

Did he say Autolite? *NM*

[Jeffrey S.]

Re: Spark Plugs

Dave
Have you ever seen an AC44 (or AC45) with the "Acnitor" in script as per the 69 judging manual? I have many R44's with the word "Acnitor" in small block letters but have never seen the other except on an original car. Could these have been only for the assembly line? All of these R44's are after 1970. I know that these superceded or followed the "Fire Ring" designation.
Your thoughts would be appreciated.
Jeff Salz

[Dave S.]

Re: Spark Plugs

Jeff,

I can't recall ever seeing a "numbered" AC plug with Acniter on it. I was not even aware they were ever used in the Flint plant. In my collection I know I have 43N, 44N, R43(rare), R44 and maybe a couple of others with Acniter on the plug. Also some tapered seat plugs like R43T also have Acniter on them. I have a friend with lots of early AC plugs. I will check with him and if I can add anything I will make another post. I was not aware that the 69 JG mentioned Acniter plugs. I learned something new. Thanks

[george romano]

Yeah HE did, why? *NM*

[Jeffrey S.]

Re: Spark Plugs

Dave
Thanks for reponding so quickly.
I also have about 8 sets of 43N's, several sets of 44N's, and many sets of numbered plug sets from all years from early 60's on including several sets dated 1969 and not one non-resistor plug has that designation either in block lettering or script. Thanks for checking with your friend. I'm interested to hear other folks thoughts also.
Jeff Salz

[Dave S.]

Re: Spark Plugs

Jeff,
We know the JG's are outstanding pieces of research but they are not perfect. It is possible that the 69 JG is wrong. I've seen many sets of numbered plugs from the 50's and 60's and as I mentioned in my other post, Acniter has never been on any of them. Its certainally possible they are out there, but they have escaped me to date. I will now keep a keen eye out for them.

[Mike Cobine]

Re: Spark Plugs - Thanks

Thanks to everyone on the info. I'd already decided to run the 45 plug as hotter is better than colder and fouling.

The striping and markings talk is a good education. If you look on eBay, you'll see pictures of several varieties and all claim to be correct for those old cars. Thin stripes, thick stripes, no stripes, ACNITER, no ACNITER, and so on.

Mike