I am looking for one. I have had some people PM me that have them. Some have drilled holes behind the carb and ahead of the distributor.
My belief is these holes were drilled after production by people that either found the carb fouled because of the crankcase venting into the base. Or they were either adding a more popular carb with no vaccum connect or, wanted to connect their power steering boost to something other than a T coming from the old AFB base plate.

So, school me, do I have the right opinion, or were 3794129s made with this hole by the factory sometime in their life. The reason I suspect they were not is I have seen about 5 different size holes in this "bung" some dead center and some offset, some holes small, some huge!

 

Just a question, where would you connect the power brake?

 

Power brake was "T'd" off of the crankcase vent into the base of the AFB/

 

Here is an example of a 129 that is late 62 or early 63 as far as I can tell, note their is no landing area or dimple for the drill hole you see in the other example. both are 129 manifolds.

 

Here is a 129 with the dimple but no drill hole. So, the question still stands......... which is the correct 63 manifold for a 340HP or are there more than one 129 Manifolds depending on date of manufacturer and/or power steering or not??????
Thought this was straight forward till I started receiving offers ????

 

I thought 62 had no fitting or place for one but 63 did?

 

Well, over 25 years ago, someone told me that the early '63 129 intakes had the boss, as shown - with no hole. According to this individual, it was the later 129's that had the boss drilled and tapped with a simple square plug.

Over the years; however, I've become more convinced that the holes and plug were installed by owners and were not factory production.

I have a July '63 SWC with its original 129 manifold - it has the boss (dimple) but no hole.

 

I agree, the hole makes the 129 modified. If you do not have the boss, dimple or whatever than I think you have a very early 63 (Dec 62 or earlier) 129 manifold. Why is that important? A NCRS or Bloom guy cannot inspect the underside of the manifold but he can see the boss or not. So it may cost you points..... any NCRS Bloom Guys/Gals here?

So assuming I have this right-

No Boss is 62 or very early 63...ie. Dec 62
Boss is 63 Jan-Sep
Boss with hole...modified by owner

I will see if I kind find any "violation" of that theory before buying a new 129 Manifold. Mine is pooched its a May 63 with boss and no drill hole. So May 63 was Pre-Mod changes by GM and July is after the Mods to the 63. You having a non drilled boss and me having the same says it was not a mid year change either.

Soooo Hole by owner?

Why is this important? If you have no boss and your car is dated later 63 then you have the wrong manifold for the car even though a 129
Man, thats going to get a response.....perhaps we find more variations?

 

Here is a comparison. The mold for the 62 corvette 340HP is 3795397
whereas the 129s we have seen above with no boss seem to be the 3795397 mold with a new number. Which I would suppose makes sense, the earlier 129s were likely rebranded 397s?
Look at the comparison 62 Corvette manifold on top, the first rendition of 129 below. This seems to support the theory that the early 129s were very early 63's and the 63's later on were an entirely different casting?

 

My very original manifold (February '63) has the boss, but no drilled hole.

 

Which tends too support the theory boss is 63 Jan+ and the no boss is a Pre Jan 63 car.
I am restoring a 63 so the difference is needed. I am rather amazed this has not be raised before, I cannot find any reference to it on the forum other than a mention that there are 2 , 129 manifolds.

Keep the info coming, if anyone has a Dec 62 Manifold on a 63SWC I would love to know boss or no boss.

 

63 DID NOT have a drilled tapped hole. Just the boss. The vacuum for brakes was from a fitting fitted to the PCV on the base of the carb.

 

I have now established that there are 3 different and distinct 129 manifolds and within a month have established their lineage.
The 129 manifold without a boss or the bump on the intake runner too cylinder number 8 indicates a 1963 casting. The 129 without the boss is a up to and including Dec 1962 +/1 one month.
The new revelation in my research is that there are now TWO 1963 Castings for the 129 manifold. The before and after Jun changeover where alot of 63 parts changed.

Drum roll please........ here is the difference.
Pre Jun1/Jul1 the 129 castings had the boss on number 8 cylinder intake runner
After Jun 1 the 129 casting had the boss on number 8 cylinder intake runner in a "different part of the runner".

Below are two 129 casting pictures take a look at the placement of the boss.

The cleaner looking manifold is a July 25 casting, the crusty other one is a March Casting.

I have included the lines to show the difference in boss position based on a straight line from the edge of 5/7 intake runner.

So, my May 63 Car requires the 129 with Boss but the boss must be as close to the edge of the 5/7 runner as the one below. So if anyone asks you from now on, there were 3 distinct 129 castings. One casting based on the 62 340HP manifold rebranded as a 129 that is valid up to and including Dec 1962 for 63 Cars. Another 129 Manifold where the boss was close to the edge of 5/7 on number 8 intake runner that is valid to Jun 1963 and another 129 Manifold that moved the boss away from the 5/7 runner to the very edge of the number 8 intake runner that is the 129 that is valid from Jul 1963 to the end of the 63 production year.
Critique if you like, this is the result of my research only.

PS NONE of these manifolds came from the factory with a hole in the Boss. So the middle example below that has the hole is not valid as a "unmolested manifold". So my car being a May 1963 I need the middle Manifold for my car to be valid for my car.

 

Then assuming the theory correct your boss should be closer to the carburetor as pictured in the post above "middle manifold".

 

Thanks to everyone for offering up the manifolds they had. I have found one that is what I need for my May 63 Car. Thanks again for the input and the offers.

 

Yes, I just looked.

The boss is closer to the carburetor

 

Further to this discussion, I was able to find out something else about the 129 that had the boss close to the carb (Pre 1 Jun Post Jan 1 1963) During the fabrication of the 129 in the latter days of May, as they approached 1 Jun they started using "Inspected and slightly visually flawed 129 Manifolds to clear out their inventory. For those in the first 4 months of 1963 none of your manifolds should have any initials on the Boss. As the later days of May started to appear, those manifolds that were sent to Quality Control that had minor flaws were inspected, stamped by the inspector (he/she) and placed into the assembly line again as the numbers of unflawed 129s started to disappear as you get to the end of May.

So if you have a 129 that has a set of initials on the Boss, then the manifold was determined to be initially flawed by line inspectors who then sent it to QA to determine boat anchor (performance or deformity issues) or acceptable (Visual issues). Boat anchors were sent back to be melted down, but flaws in visible casting numbers, like the firing order, or the stock number, or other embosses that were considered superficial, would show up again later on original cars, at the latter end of the production cycle to clear out old inventory before a new casting occured.
Then, 1Jun-ish the new casting with the Boss moved farther away from the Carb began. Flawed manifolds for the new casting then migrated to QA who repeated boat anchor vs minor flaws and then interjected them into the end of production, of that casting, whenever that occured. So I would expect as GM stopped making the 129, alot of cars came out with slightly flawed + "QA inspectors initials" as they entered the production end of the 129s

I would expect that this applies to all manifold castings no matter whether cast iron or Aluminum. Interesting to know though it applies to a 63 and is just another tidbit. So if you are at all curious and have end Dec 1962 car, or an end of May car, or end of Production year car, check to see if you have initials stamped/scratched anywhere. No idea where they would be in the pre Dec 31/62 129 because they had no boss ??

 

The boss was put there for a reason. Was it used on other applications where it was drilled from the factory? If it is a "Corvette Only" manifold, why add the boss and never use it? Maybe a CA only emission thing?

 

According to Colvin's "Corvette by the Numbers" the aluminum intake 3794129 was a single use - the 1963 340HP SHP engine, and the drawing in this same book details no vacuum boss.

The newer 384461, which was only used for the 1965 365HP and the 1966 350 and 365 HP engines is the updated 129 for these years.

Further quoting Colvin under the description of the 461: "The blueprint of this (461) intake shows the addition of the power brake booster boss behind the carb mounting pad (implying that the 129 does not). But then it goes on to say "other Chevrolet documentation shows that the 129 manifold had this boss."

Taken together, it sounds as if the 129 intake went through a couple of mid-production run modifications to add the power brake vacuum boss, kind of like the mid-1967 3917291 heads that were the replacement for the 462 heads, but that had the cast in temperature sensor boss, which not drilled and tapped initially for use in 1967s, but later was to accommodate the changed position of the temperature sensor for 1968.

Add this to it: Initially 129s had no bosses, then had bosses which were not drilled, followed by ones that were. Since parts casting and machining were not first-in, first out in those days, there can be examples of mismatched dates where some with drilled bosses are earlier dated than some without the bosses cast in at all.

Running changes were not at all unusual in this industry.

 

Agree. I don't see many owners tapping that boss. I would think most tapped ones came from the factory that way.