Is this a can of worms?

[Don L.]

I am trying to learn what the right part number is for a '72 SB vac advance control. My friendly neighborhood parts house says the issue of part number "correctness" is complicated. Specifically, it says "There is much confusion among knowledgeable persons regarding correct usage of distributor vacuum advance controls...." It goes on to say "Before ordering, please have a qualified judge tell you which number is correct for your car if you are having it judged". I have numbers on mine, but can't find a reference, or any information in archives to help understand what is correct for the engine. My application is 1972 SB/4 spd/non-A/C.

Any advice available out there today?

[Terry M.]

Re: Is this a can of worms?

And what is wrong with the vacuum canister numbers that are given in the TIM&JG? Or are you interested in function over TFP?

[Gary C.]

Re: Is this a can of worms?

Attached is a summary of the "Duke's" previous posts on vacuum advance cans. Gary....

[Don L.]

Re: Is this a can of worms?

Actually, I felt similar confusion after reading the JG. It lists a 437 16, but related footnotes seem (to me) to hint at some potential for controversy. I'm hoping to verify through multiple original cars and others that have had experience. JG says "There may be other instances of inconsistencies, but we belieive this list is accurate." What's the timing of this note in the JG? Has there been any NEW info gained since it was written? Thought it to be a fair question.

Now that Terry mentions, is there any advice on function vs TFP?

[Duke W.]

Re: Is this a can of worms?

You will have to dig deep to find a NOS VAC. GM and the aftermarket consolidated part numbers over the years, and, today, the only manufacturer of VACs is Standard Motor Products and all are stamped "B-XX" to identify them including those sold by GM dealers and "Delco".

The pdf referenced with a summary of my comments applies to setting up a spark advance map for optimum performance and fuel economy. In the case of most emission controlled engines ('68-up) and some pre-emission controlled engines, neither the OE VAC nor the "ported" activation meets the requirements for maximum performance/economy, so they must be modified with one of the three listed VACs (based on idle manifold vacuum), and converted to full time vacuum advance.

If you want a VAC that matches OE specs as close as possible, google to find the "Lars" paper, which is on several web sites (see the nearby thread similar subject). It lists all the currently available VACs, and you should find one close to OE spec. However, it will not have the stamped original GM number, but a "B-number".

The VAC is only worth 3 total points in judging - two for originality and one for condition. In chapter judging, IF the book lists a VAC number that I believe is correct and the car does not have this VAC I deduct one point for "OE replacement". If the book does not list a number I usually don't deduct, even if I KNOW the installed VAC is not the correct OE part.

Duke

[Terry M.]

Re: Is this a can of worms?

That note was put in the manual when the vacuum canoster information was added. I'm kind of guessing, but I think around 2003 or 4. The numbers came from the Delco Remy technical information catalogs. We have seen in other situations where the cataloged parts never made it onto the car -- thus the note.

To the best of my knowledge no revisions are in line for this data.

[William C.]

Re: Is this a can of worms?

What is the part number of the distributor? We have the Delco part number references for the vacuum advance used with each assembly. Again, are you looking at show or drive, as reproductions I have tested do not always meet (or even come close to) the OE specs.

[Terry M.]

Re: Is this a can of worms?

I am trying to learn what the right part number is for a '72 SB vac advance control. My friendly neighborhood parts house says the issue of part number "correctness" is complicated. Specifically, it says "There is much confusion among knowledgeable persons regarding correct usage of distributor vacuum advance controls...." It goes on to say "Before ordering, please have a qualified judge tell you which number is correct for your car if you are having it judged". I have numbers on mine, but can't find a reference, or any information in archives to help understand what is correct for the engine. My application is 1972 SB/4 spd/non-A/C.

Any advice available out there today?

Don how about sharing with us what version of the TIM&JG you have? My version (Fourth Edition) doesn't have that language in it (or at least I don't find it), and I suspoect you are using an earlier version.

[Don L.]

Re: Is this a can of worms?

Thanks Bill and Terry.

Bill: my model year 1972/August 11, 1971 built SB (base) engine has distributor # 1112050. Think my preference is in show (NCRS #'s is my objective), however, if the correct unit is lousy and I get a recommendation to forego the points for improved performance, I'm very interested.

Terry: Hmmm. I too am looking at the fourth edition JG. Look at page 64, about 2/3 down the page where the double asterisks are. The double asterisk is noting the VAC info higher on the page. My earlier quote (see above post) is directly from this page. See it? It's the last sentence in the note.

My current situation is that I have a lead on a 437 15 VAC. The 437 part # is right for NCRS, but the "15" degrees may make it incorrect, thus my confusion/question/post.

Thanks again.

[Jack H.]

Re: Is this a can of worms?

Methinks the table recited in the JG (437 16) is in error. The same vac advance was used for '71 and '72 base engine SB's (as well as other engines) and I have the factory original distributor in my '71. It's clearly embossed '437 15' as the picture shows. I suspect the '437 16' reference in the JG is a typo as I also have an NOS 'backup', in original box, that's embossed the same way!

[Don L.]

Re: Is this a can of worms?

UH OH.

This may indeed be the "can of worms" I feared/referenced when posting this thread. Thanks Jack.

The vac I have currently is not a 437, but IS a 16. The plot thickens.

Any other views?

[Terry M.]

Re: Is this a can of worms?

Terry: Hmmm. I too am looking at the fourth edition JG. Look at page 64, about 2/3 down the page where the double asterisks are. The double asterisk is noting the VAC info higher on the page. My earlier quote (see above post) is directly from this page. See it? It's the last sentence in the note.

Don,
I see the quote from the supplier, which is not a quote from the TIM&JG:
"Originally Posted by Don Lowe (44382)
I am trying to learn what the right part number is for a '72 SB vac advance control. My friendly neighborhood parts house says the issue of part number "correctness" is complicated. Specifically, it says "There is much confusion among knowledgeable persons regarding correct usage of distributor vacuum advance controls...." It goes on to say "Before ordering, please have a qualified judge tell you which number is correct for your car if you are having it judged". I have numbers on mine, but can't find a reference, or any information in archives to help understand what is correct for the engine. My application is 1972 SB/4 spd/non-A/C."

I guess I am missing your quote from the TIM&JG -- perhaps this thread has gotten too long, and I don't have the patience to keep up with it.

Notwithstanding that I would remind you (and others) that the TIM&JG(s) are not written to be parsed by judging field "lawyers." Pull a sentence out of context, and you may be able to make it say whatever you want. Whether you can sell that interpretation to the judge on the field is another matter.
That whole paragraph with the double asterisks tells you where we got the information (which is the same as I posted someplace above), that in one case we found it to be in error, and that the Chevrolet parts books can be in error. As I told you that up to now we have no information that would cause us to change what is listed in the TIM&JG.

Jack,
No typo on our part -- but you can challenge the Delco Specifications if you want -- I gave up tilting at windmills a long time ago. As noted we have found other errors here, so maybe there are more -- that is exactly what that paragraph was intended to tell people. You might try to get some other data points about the 437 stamping, and submit your findings for possible inclusion in the next revision of the TIM&JG.

One should also remember that with the distributor cap installed often one can only see part of the stamp on the vacuum canister. All this may be much ado about almost nothing.

[John H.]

Re: Is this a can of worms?

"There is much confusion among knowledgeable persons regarding correct usage of distributor vacuum advance controls...." It goes on to say "Before ordering, please have a qualified judge tell you which number is correct for your car if you are having it judged".

Terry -

That quote isn't from the JG - it's part of a "Tech Note" on vacuum advance units in the Paragon catalog.

[Stuart F.]

Re: Is this a can of worms?

Just use Caution because many of the repro VAC's may be stamped correctly, but they don't meet specs (as checked with a Mityvac). I had to send some back - so it does come down to whether you just want it to look correct or to function properly.

Stu Fox

[Terry M.]

Re: Is this a can of worms?

Terry -

That quote isn't from the JG - it's part of a "Tech Note" on vacuum advance units in the Paragon catalog.

Thanks John. I was sort of wondering who the local parts store was. I was pretty sure it wasn't AutoZone or Kraigens or NAPA.