1955 Spark plugs

[Benjamin C.]

What are the correct spark plugs for a 1955 265CI ?

[Joe L.]

Re: 1955 Spark plugs

What are the correct spark plugs for a 1955 265CI ?

Benjamin------


According to GM it was an AC C43, aka GM #5612002.

[Duke W.]

Re: 1955 Spark plugs

Those plugs will foul out very rapidly because they are way too cold, assuming you can find them. They've likely be out of production for decades. AC heat range 5 is what you should use, but only resistor plugs are available, and the functionally "correct" one would be R45. You can also buy non-resistor plugs in other brands equivalent to AC heat range 5 such as the NGK B4 and Denso W14-U.

BTW I used C43 plugs hot lapping Kent with my SWC back in the sixties, and they were just right for that service. The OE 44s fouled frequently, but 45s turned out to be just right for normal road and highway operation.

The "C" stands for "commercial" and they have larger electrodes than standard passenger car plugs.

Read the similar threads at the bottom of the page.

Duke

[Jeffrey S.]

Re: 1955 Spark plugs

According to the 1956 AC Delco Wholesale Catalog, the plug was an AC 43-5R. This was the older smooth porcelain (no rings). The catalog is actually dated 10/54 and I have a reprint. The next catalog I have is dated 7/57 and shows 44-5 for Standard use and 43-5R for severe use. Page 104 of Noland Adams book indicates the plug was 43-5R COM (Commercial). Hope this helps.
Jeff

[John S.]

Re: 1955 Spark plugs

According to the 1956 AC Delco Wholesale Catalog, the plug was an AC 43-5R. This was the older smooth porcelain (no rings). The catalog is actually dated 10/54 and I have a reprint. The next catalog I have is dated 7/57 and shows 44-5 for Standard use and 43-5R for severe use. Page 104 of Noland Adams book indicates the plug was 43-5R COM (Commercial). Hope this helps.
Jeff

The judging guide also says 43-5R COM. It would be nice to know whether the plug originally on the 55 corvette was a 43-5R or a 43-5R COM. Jeff, are you able to post a picture of the page in the catalog which has 43-5R listed as the correct plug?

[Jeffrey S.]

Re: 1955 Spark plugs

The judging guide also says 43-5R COM. It would be nice to know whether the plug originally on the 55 corvette was a 43-5R or a 43-5R COM. Jeff, are you able to post a picture of the page in the catalog which has 43-5R listed as the correct plug?

Here you go.

[Joe L.]

Re: 1955 Spark plugs

According to the 1956 AC Delco Wholesale Catalog, the plug was an AC 43-5R. This was the older smooth porcelain (no rings). The catalog is actually dated 10/54 and I have a reprint. The next catalog I have is dated 7/57 and shows 44-5 for Standard use and 43-5R for severe use. Page 104 of Noland Adams book indicates the plug was 43-5R COM (Commercial). Hope this helps.
Jeff

Jeff-----


Yes, I was in error. For 1955, GM says the AC 43-5R, aka GM #5569889, was used for all Corvettes, both 6 cylinder and V-8. The AC C43 was used for 1956 Corvettes. I think I got it confused because I thought that different plugs were used for 1955 6 cylinder versus V-8.

[John S.]

Re: 1955 Spark plugs

Jeff-----


Yes, I was in error. For 1955, GM says the AC 43-5R, aka GM #5569889, was used for all Corvettes, both 6 cylinder and V-8. The AC C43 was used for 1956 Corvettes. I think I got it confused because I thought that different plugs were used for 1955 6 cylinder versus V-8.

What about the 43-5 Com, GM#5569831, that is listed for 53-55 Corvettes in the july 55, corvette parts catalog? it shows a 44-5, GM #5569761 for the 6.

[Jeffrey S.]

Re: 1955 Spark plugs

Jeff-----


Yes, I was in error. For 1955, GM says the AC 43-5R, aka GM #5569889, was used for all Corvettes, both 6 cylinder and V-8. The AC C43 was used for 1956 Corvettes. I think I got it confused because I thought that different plugs were used for 1955 6 cylinder versus V-8.

Joe,
On the same page, the plugs listed for '53-'54 6 cylinder is the 43-5. For '56 a 44 was used for moderate use and the C43 for heavy duty service. I'm pretty sure that the 44 was what was delivered from Flint in '56.
Jeff

[Joe L.]

Re: 1955 Spark plugs

Joe,
On the same page, the plugs listed for '53-'54 6 cylinder is the 43-5. For '56 a 44 was used for moderate use and the C43 for heavy duty service. I'm pretty sure that the 44 was what was delivered from Flint in '56.
Jeff

Jeff-----

The information that I have shows the standard plug for 1956 Corvettes was the AC C43. The AC 44, aka GM #1559492, is shown as the "hot operation" plug.

What does it say in the 1956 Corvette owner's manual?

[Joe L.]

Re: 1955 Spark plugs

What about the 43-5 Com, GM#5569831, that is listed for 53-55 Corvettes in the july 55, corvette parts catalog? it shows a 44-5, GM #5569761 for the 6.

John------


My 1956 parts catalog does not show the GM #5569831 as being applicable to any Corvette.

The 56 catalog shows the AC 44-5, GM #5569761, as being the standard plug for "ALL" 1949-55 except 2 ton. However, very often in GM parts cataloging "ALL" does not include Corvette. The same catalog shows the AC 43-5R, GM #5569889, as being the standard plug for 1953-55 Corvette.

[Jeffrey S.]

Re: 1955 Spark plugs

Jeff-----

The information that I have shows the standard plug for 1956 Corvettes was the AC C43. The AC 44, aka GM #1559492, is shown as the "hot operation" plug.

What does it say in the 1956 Corvette owner's manual?

Joe,
I don't have access to a '56 Corvette owner's manual- just the passenger car manual. I have almost every AC Delco sparkplug catalog from 1954 through the 80's and that is where I take the applications from in addition to Noland Adams' books. Your knowledge and resources are far superior to mine so I will defer to you,
Jeff

[Joe L.]

Re: 1955 Spark plugs

Joe,
I don't have access to a '56 Corvette owner's manual- just the passenger car manual. I have almost every AC Delco sparkplug catalog from 1954 through the 80's and that is where I take the applications from in addition to Noland Adams' books. Your knowledge and resources are far superior to mine so I will defer to you,
Jeff

Jeff-------


With respect to spark plugs, "funny things" can happen, either in spark plug tables or, even, GM parts catalogs. Usually, the owner's manuals will give the correct, original spark plugs. Maybe someone else will have an original owner's manual.

[Jeffrey S.]

Re: 1955 Spark plugs

Here's what is written by Noland Adams on page 128 of his book with respect to '56-'57 plugs:
"Most 1956 and 1957 Corvette engines were built with AC-44 spark plugs installed. This practise continued until March of 1957 when AC46-5 plugs were fitted. Car number E57S103098 is the earliest car reporting this revision. These plugs continued until E57S103268, when they were changed to AC-46." Additionally, Technical Service Bulletin DR number 295, May 22nd, 1957:
"Corvette Engine Spark Plug Recommendations
Type Type driving Part No.
AC-46 City 1559494
AC-44 Town & Country 1559492
C-43 Comm. Heavy Duty & High Speed 5612002
C-42-1 Comm. Racing 5612140
Above information will be inserted in the
Corvette Operations Manual and will appear
in the next edition."
Jeff

[Gary C.]

Re: 1955 Spark plugs

Must give credit to Jeff Salz for allowing me to take photos of his spark plugs at Carlisle years ago for use in the 56-7 Judging Manual.

Attached are references to the 56-7 Owner's Manual changes and GM references to 56-7 plug changes.