big block intake manifold

[Joe L.]

Re: 198 manifold divider is machined

Mark-------

How is it possible to tell what the as-cast height of the plenum divider is between your examples of the 3933163 and 3933198 manifolds if both show evidence of the divider having been machined? In other words, how would one know what the "starting point" was before machining was performed on the divider?

[Michael H.]

Re: Addendum

Not sure if this is of any help but I still have the HD parts list that came to my office in early 1968. In the list is the original 67 L-88 manifold, #3886091. There's a line drawn through the number and a hand written #3947083 in it's place. The revision was not written over the copy but instead on the original and all copies would then show this change. Unfortunately, there's no date listed for the change.

Many of these early HD parts would be slightly revised production parts that would then be assigned a new part number. Some parts went through several changes in just a few months and many would retain the first casting # change. .

[Mark #28455]

Re: 198 manifold divider is machined

The machining only removed the center portion of the divider, it did NOT open up a full square plenum like on aftermarket intakes. There remains at the front and back of the plenum about a 3/4" stub of the original divider casting. Make sense?
Mark

[Mark #28455]

Re: Addendum

I noticed the 7083 part number was still being used as of my 1973 parts manual. In addition, I noticed that my 198 and my 163 "L88 style" and my LS6 manifolds used a screwed in thermostat bypass nipple.
Mark

[Joe L.]

Re: 198 manifold divider is machined

Mark------

Yes, I'm aware of the configuration you describe. In fact, the "stub" section that you describe is exactly the same for all five manifold castings---the 3885069, 3933163, 3933198, 3919851, and 3919878. The point that I'm getting at is how do we know that the center section of the plenum divider (i.e. the part that is machined down) was not originally different as-cast? It's really a moot point as far as functionality goes, since the machining operation determines the final configuration of the divider. What I'm trying to understand is what were the differences in the 3933163 and 3933198 castings. There had to be SOME difference. Plus, that difference had to involve something that would enable the "conversion" of a 3933163 casting to 3933198 "casting"-----otherwise it would not have been possible to grind off the last numerals and replace them.

Also, as far as the by-pass fittings go, I was sure that the 3933198 (and, for that matter, the 3963569 1971 LS-6) manifolds used a threaded type bypass fitting. I was not sure that the 3933163 did, though. However, I have since confirmed that it did. So, that's not the difference in the castings (castings for the pressed-in versus threaded fittings are different; it's not just a machining operation).

The 3885069 and 3933163 differ in that the former has no water (heater hose) fitting on the right front of the manifold and the latter does. However, the 3933198 has the same fitting as the 3933163. So, that's not the difference in the 3933163 versus 3933198 castings. Neither manifold was originally equipped with an oil splash shield, so that's not the difference.

So, when we eliminate the possible differences between the 3933163 and 3933198 castings, we so far come up "dry". However, we know the following:

1) There was SOME difference. GM does not change casting numbers for absolutely no reason, at all. As subtle as the difference might be, it's there;

2) The difference in the castings is such that the 3933163 can be converted to a 3933198 via, apparently, a machining operation. Otherwise, there could be no "re-stamped" manifolds. I consider that the conversion is due to the machining operations since nothing else is or could be done to the manifold subsequent to casting.

The only thing I can come up with is that the as-cast height of the CENTER SECTION of the plenum divider was different between the 2 castings.

[Mark #28455]

I don't think they would have bothered

If the only difference were the divider height in the area to be machined out, why would they bother? It wouldn't make any difference in helping the milling operation, so it wouldn't be worth the money to re-design a whole casting just for that change. I also didn't notice any "stupid little" changes like an obvious change in the coil mounting provisions, carb mounting height, etc. The only thing that strikes me now may be a change in the grooves on the plenum base to help compensate for the fuel distribution with an open plenum. Unfortunately, my 163 is in use and I'm too lazy to pull the carb just for a peek would you have two manifolds you could compare?
Thanks,
Mark

[Joe L.]

Re: Addendum

Michael------

I believe that the reason that the 3886091 was crossed out and replaced by 3947083 is that the 3886091 was an error. GM #3886091 is not a manifold, at all. It's the GM part number for the Holley list #3418 carburetor used for 1967 L-88.

From what I can tell, there were 2 possible PART numbers used for 1967 L-88. These were GM #3878290 and GM #3886092. These PART numbers may or may not have consisted of CASTING numbers 3886093 and 3885069. It's also very possible that either PART number manifold could have been manufactured from either CASTING number.

For 1968, GM shows that manifold PART number 3885069 was used throughout the year. However, that does not mean that it actually was. Also, and very importantly, it does not mean that the GM PART number 3885069 was always manufactured from the 3885069 CASTING.

I believe that sometime in 1968 PRODUCTION, the manifold for L-88 applications did change to the GM #3933198 CASTING (whether that be a "converted" 3933163 casting or, even, a casting showing the 3933163 casting number). This manifold was known as GM PART #3947083 as the revised information on your documents indicate. However, it's VERY possible that all GM PART number 3947083 manifolds were not made from either the 3933198 or "converted" 3933163 CASTINGS. Some could easily have been made from the 3919851 or 3919878 castings. From what I can tell, those castings were identical to the 3933163 and 3933198 or, at least, close enough that they could have been converted via a machining operation to the GM PART number 3947083 manifold.

VERY INTERSTINGLY, 1967 model year parts publications contain no footnote regarding the GM PART #3886092 (1967 L-88) manifold. However, the 1968 model year published parts information regarding the same manifold PART number now shown as applicable to 1967-68 Corvette HD applications DOES CONTAIN a footnote. It says that the "bypass fitting" hole may need to be plugged with a 1/2-14 pipe plug ( I believe that the reference to the "bypass fitting" hole really means what we know as the heater fitting hole as all big blocks used external bypass and the traditional bypass fitting would never need to be plugged for any application). Since the GM CASTING # 3885069 had no heater hose fitting on the right front but the GM CASTING number 3919851, 3919878, 3933163 and 3933198 DID have such a fitiing, this strongly implies that by late 1967 when the 1968 parts information was first published, the GM PART #3886092 may have used castings other than the 3885069 for some or all examples.

For 1969, the L-88/ZL-1 continued to use the GM PART number 3947083 manifold. However, by this time, I expect that only the 3933198 or "converted" 3933163 CASTINGS were used.

Also, of note is that early 1968 Chevrolet SHP big block engines (L-72 and L-78 used in other Chevrolet models) used intake manifold GM PART number 3888099. This manifold generally used the same GM CASTING number manifold as 67-68 Corvette L-88---3885069. However, it's also possible that other castings, such as the 3919878 and 3919851 were also used. The fact that most, if not all, examples of these castings that have been found have later 1967 casting dates implies that this usage was during the late 1967-early 1968 model year.

Later 1968-1969 L-78 and L-72 used GM PART number 3947084. This manifold generally used GM CASTING number 3933163. However, it's very possible, but more unlikely, that some examples of the PART number 3947084 manifold used other castings.

The GM PART number 3947083 (68-69 L-88/ZL-1)manifold was finally discontinued without supercession in May, 1979. The GM #3947084 (68-69 L-78 and L-72) was discontinued without supercession in October, 1980. Interestingly, another GM PART number manifold was released prior to the discontinuation of either of these, but never superceded either. That manifold is the GM #3933163----a maifold with the same PART number as the CASTING number used for the 68-69 manifolds. As far as I can tell, it's identical to the manifold once known as GM PART number 3947084.

[Joe L.]

Re: I don't think they would have bothered

Mark-----

I think that I have examples of both in my "used" parts collection. Unfortunately, the "used" collection is virtually impossible to find anything in. It's, essentially, "long-term" storage and I only go there if I REALLY, REALLY, need something that I know is in there. So far, that's only happened once in about 10 years.

As far as the "grooves" go, they might be different between the 2 castings. However, if so, then it would not be possible to "convert" a 3933163 to a 3933198. As I mentioned, I consider the difference had to be something that could be changed by a machining operation.

I agree that it would make little sense to have different castings which differ only by the height of the cast-in plenum divider. However, that does not mean it wasn't done. For example, it may be that the original intent was to have a manfold with a ceneter plenum divider of reduced height compared to the 3933163 WITHOUT the need for further machining of it. At some point after the casting was designed, perhaps it was decided that the center divider needed to be further reduced in height. So, the already lower center plenum divider was further reduced in height by machining. This is just one possibility---there may have been other reasons, too.

[Michael H.]

3886092/3947083

Joe,

Sorry, my mistake. I meant to type 092 but instead typed 091. I always remembered both numbers as these items were a set, so to speak. The carburetor was released for use with the open plenum intake manifold. Here's the scan of the original page that shows the correct numbers. As mentioned previously, the number was crossed out on the page as it arrived in early 1968. Later, time permitting, I'll see if I have anything else of interest on this part number. (love the 37 gal fuel tank for Camaro. Sure wish I still had all those parts today!)

[Mark #28455]

there has to be some difference

If the factory could have simply machined down the divider of the 163 intake, they would have stopped casting the 198's ASAP (probably cost a lot to cast an extra, very limited production part when the 375/396 intake was much more common). I question the pedigree of most of the "restamped" 163 intakes that I have seen on e-bay as the cut out divider looks nothing like my 198's.

Mark

[Joe L.]

Re: there has to be some difference

Mark-----

It would seem that the 3933198 casting had no logical reason for existence. Of course, there would have been a cost savings to just have one manifold casting (i.e. the 3933163), and use it for all applications, machined appropriately. However, that assumes that the tooling for the 3933198 was not already created. Once the tooling was created, most of the cost of the additional casting was "behind them". So, there would have been no real cost to continuing production of both castings. Given the casting numbers, I'm quite sure that both manifold castings were designed and tooling created at just about exactly the same time.

I consider that the 3933198 casting number was also the PRIMARY ID number (but, perhaps, not the ONLY ID number) for the GM PART #3947083 manifold. That's why the foundry or engine plant went to the trouble of grinding and restamping the number on 3933163's "converted" for creation of GM PART #3947083 manifolds. The GM #3933163 was likely the PRIMARY ID number (but, perhaps, not the ONLY ID number) for the GM PART #3947084 manifold.

Whether all extant 3933163 manifolds with the last 2 or 3 characters ground off and restamped as 3933198 were originally that way, I have no way of knowing. It may be that the "route" by which the "conversions" were manufactured differed. For example, it MAY be that the 3933198 manifolds were finish machined IN ENTIRETY at the Tonawanda engine plant. So, the machining of the center divider plenum was done a certain way. At the same time, the "conversion" of the 3933163 castings to 3933198, including grind and restamp, was possibly done at Winter's Foundry prior to delivery of the castings to Tonawanda. There are probably numerous other scenarios that could be conjured up, too. The fact of the matter is that the grind and restamp was rather crudely done. That makes it all the more easy to "recreate" it.

As far as I know, there are known-original cars which have the ground and restamped number on the manifold.

[Steve Antonucci]

Re: 3886092/3947083

Joe,

I can tell you for a fact that the '163 intake uses the threaded nipple at
the front of the intake. SO, that's not the difference.

Also, I have personally seen '163 intakes with January 1968 casting dates. I
would assume these were on production cars. However, all of them were date
verified as loose items, not on cars.

Steve

[Steve Antonucci]

Re: 3886092/3947083

Mike,

Do you remember seeing a thread here that seemed to indicate that the '198
intake flowed better than the '163? Joe may be right however in that it is
more BB SHP folk-lore.

Steve

[Michael H.]

Re: 3886092/3947083

Steve,

I don't remember reading that. I think most of the changes that were made on these BB manifolds were for other reasons. The basic structure and layout of the runners was pretty much the same if I remember correctly.

[Steve Antonucci]

Re: 3886092/3947083

OK - Now you have me scratching my head......