Late C4 Air Filter Date/Production Codes

[Pat F.]

I have conducted a couple of surveys on the Air Filter Date/Production Codes located on the side of the Air Filter.

It was felt that the first digit was the year, the second a letter was the month, then two digits for the day of the month and then either a D-Day,N-Night or M-Midnight, shift designation. See attached. The first Air Filter with the 2 designation for the year on a AC Delco is thought to have been manufactured in 2002 and not in 1992.

We thought that we pretty much had it under control until we received some photos of AC Rochester and AC Delco Air Filters with a M and a N month code. Initially it was thought that the letters A-1 and L-12 represented the month date code. However, the recent discovery of the M and N month date codes has us looking at these month codes again.
Could the cause of the M-13th month and N-14th month be caused by the deletion of the I-9th month as not to confuse it with the number 1?

If we got around that, how do we explain the N month date code.

Almost 98% of the monthly date codes that I have in my data base correspond to the build date code of the Corvette.

I have monthly date codes of A, B, C, D, J, K, L and now M and N.

If you haven't sent me information in the past regarding this matter please let me know what the monthly date code is on any AC Rochester or AC Delco Air Filter that you have for the 93-96 model years.

Also, if you have any explanation for the M and N monthly date code or some one that we could reach out for, please let me know.

The latest addition of the N monthly date code came from the collection of Don Griffin.

Thanks

[Pat F.]

Re: Late C4 Air Filter Date/Production Codes

Come on guys, surely someone can make a contribution.

[Chris G.]

Re: Late C4 Air Filter Date/Production Codes

This is an OLD thread. I see the picture here of an air filter with a Month date of " N" . What month would that equate to given M=December skipping "I" . I have been looking for a 95 filter and sorting date codes.

[Edward J.]

Re: Late C4 Air Filter Date/Production Codes

It may be possible that Rochester div. end sometime in early 95, since A/C Delco took over the (N) may be the last letter it produced. which could be Jan.1995??? I would also say Joe L. would know the time frame when Rochester ended its era.

[Pat F.]

Re: Late C4 Air Filter Date/Production Codes

One thought was that the plant did not use the letter I as not to confuse it with a number 1. This has been done in the past in other applications. There is not enough data out there to support this.
With the deletion of the I, then N would become a data code for December.
At this point no one seems to have a real handle on the date code on these air filters.

[Ed H.]

Re: Late C4 Air Filter Date/Production Codes

Pat,
I have a (AC DELCO A1097C 4J17N) that I acquired for judging purpose on my 1993 ZR-1, and my 1990 L-98. Just for grins
can you tell me when that filter was manufactured. No deducts on either car. They both received Cross Flag award. giggle/giggle.
And Chris, what is the build date of your car. This filter may be in the 6th month rule.

[Pat F.]

Re: Late C4 Air Filter Date/Production Codes

Ed, for what is worth, here is the information in the respective NCRS Judging Manuals.
1992-93 NCRS Judging Manual -"The filter element is AC (The word Sparkplug should have been in the text) A1097C". A photo of a ACSPARKPLUG A1097C is shown on page 119.
1994-96 NCRS Judging Manual- "The filter element is AC A1097C. The A1097C 1994 and 1995 Corvette air filter has AC ROCHESTER A1097C stamped in black, along with a production code, on the end fold of the paper element with a dot matrix style print. The early 1996 Corvette, produced prior to January 1996, air filter may have AC ROCHESTER A1097C or AC DELCO A1097C stamped in black, along with a production code. The 1996 Corvette, with production of January and later, air filter has AC DELCO A1097C".
This information is on page 135 of the 1994-96 NCRS Judging Manual.
Therefore the AC DELCO air filter did not come into play until sometime at the end of 1995 or early 1996.
I have a AC ROCHESTER A1097C air filter that came off a 1995 Corvette with a November 1994 Build Date of and a date code of 4K17D on the air filter.
The date code of 4-1994, K-either October or November if you exclude the letter I as not being utilized in assigning date codes to avoid confusion with the number 1, 17-17th Day and D-May indicated Day Shift. This air filter was provided to me by the original owner who removed it from his 1995 Corvette.
I am attaching a photo of this air filter.
This is all just my opinion.

[Ed N.]

Re: Late C4 Air Filter Date/Production Codes

Ed, for what is worth, here is the information in the respective NCRS Judging Manuals.
1992-93 NCRS Judging Manual -"The filter element is AC (The word Sparkplug should have been in the text) A1097C". A photo of a ACSPARKPLUG A1097C is shown on page 119.
1994-96 NCRS Judging Manual- "The filter element is AC A1097C. The A1097C 1994 and 1995 Corvette air filter has AC ROCHESTER A1097C stamped in black, along with a production code, on the end fold of the paper element with a dot matrix style print. The early 1996 Corvette, produced prior to January 1996, air filter may have AC ROCHESTER A1097C or AC DELCO A1097C stamped in black, along with a production code. The 1996 Corvette, with production of January and later, air filter has AC DELCO A1097C".
This information is on page 135 of the 1994-96 NCRS Judging Manual.
Therefore the AC DELCO air filter did not come into play until sometime at the end of 1995 or early 1996.
I have a AC ROCHESTER A1097C air filter that came off a 1995 Corvette with a November 1994 Build Date of and a date code of 4K17D on the air filter.
The date code of 4-1994, K-either October or November if you exclude the letter I as not being utilized in assigning date codes to avoid confusion with the number 1, 17-17th Day and D-May indicated Day Shift. This air filter was provided to me by the original owner who removed it from his 1995 Corvette.
I am attaching a photo of this air filter.
This is all just my opinion.

Pat, interesting enough, my car has a build date of 11/1/94 and my original air filter is 4k30M. Could be interrupt as October 30, 1994 - Morning or M for midnight? Or, if the I was in fact excluded, it would then be November. But, if my car was built on November 1, 1994, would it be possible that the factory installed an air filter with a build date of November 30, 1994, instead of one reading October 30, 1994?

[Pat F.]

Re: Late C4 Air Filter Date/Production Codes

Ed, I sent you a regular email on this topic.
Pat

[Pete B.]

Re: Late C4 Air Filter Date/Production Codes

I thought we determined that there might have been 2 sources, one dated them and the other did not.
This same filter carries over into C5's and we see the same inconsistencies.
Its cool when it works, but its truly hit or miss.

[Floyd B.]

Re: Late C4 Air Filter Date/Production Codes

I haven't seen mention of the "sample size" of the database. When building any statistical model, sample size is a critical factor when determining the margin of error (i.e. the trustworthiness of the model). Given that '93 through '96 model year production churned out more than 87k units. To obtain 99% confidence level and 2% margin of error you would need a sample size of almost 4000. I would agree that is probably overkill for our purposes but even a 90% confidence level and 5% margin of error would require a sample size of 270. In this case, I wouldn't trust a model that wasn't built using a sample size that numbers at least in the 100's.

[Chris G.]

Re: Late C4 Air Filter Date/Production Codes

Works for me. I have spent about $400 bucks on air filters trying to get a matching build date. I am going with what I got!!

[Pat F.]

Re: Late C4 Air Filter Date/Production Codes

Pete, I just sent you a PM.
Thanks, Pat