big block intake manifold

[tim sargent]

I have a big block aluminum square port, open plenum, dual plane manifold. The casting number is 3919851, I do not find this casting number in my reference material. It was cast 6 21 67. It appears to be an L-88 type manifold with the cut down plenum. Does anyone know the OEM application for this manifold?
Thank you Tim

[Joe L.]

Re: big block intake manifold

Tim-----

There is no original application that's ever been verified for this manifold. It's very possible that it was used only in SERVICE. However, it's also possible that it was used on some 1968 Corvette L-88's. I don't know if any 1968 with L-88 has ever been found which had one of these on it, though. Of course, given the fact that it's not considered correct for such applications it may be that even if one found such a manifold on a 1968 L-88, they'd remove it in favor of a "correct" manifold casting number. So, we may never know.

Generally, for 1968 L-88's it's considered that either the 3885069 or the 3933198 manifolds were used. However, there may have been another and, if so, the "another" would be the GM #3919851.

Does the "cut down" plenum on this manifold appear to be a feature of the manifold CASTING or does it appear that it's a feature of the manifold MACHINING or FIELD MODIFICATION?

[tim sargent]

Re: big block intake manifold

Joe

Thank you for your response, interestingly I have a 1968 L-88 "IT" engine and it has te "3933163" intake manifold, which is also considered wrong as it was apparently also a service only item or COPO Camaro item.
The "3919851" manifold plenum appears to be machined to open it up not "as cast".The casting number is cast differently from the "163" and "069". If you are interested I can send you pictures if you E-Mail me direct TAS@Directcon.net.

[Jay G.]

Re: big block intake manifold

The 3933163 retangular port intakes were OEM on 396/375 HP L-78 solid lifter cars such as Camaros and Novas. Mostly big block apps not sure if used on Z cars as well.

[Steve Antonucci]

Re: big block intake manifold

Tim,

The 3933163 was not only a COPO engine intake. It was used in all production
L/78 & L/72 engines in 1969. It was also used in 1968 production for the same
engines. However, I'm not sure if it was used throughout the entire '68 year.

There have been a couple of documented ZL-1's that used the '163 intake with a
modified plenum. Some had the last three digits ( 163 ) ground off and "198"
digits stamped in their places.

As far as I can tell, the plenum was essentially the only differnce between
the two intakes.

Steve

[Steve Antonucci]

Re: big block intake manifold

Here's essentially the exact intake I was referring to ( see the link ).

Steve

http://cgi.ebay.com/ebaymotors/1969-CAMARO-ZL-1-L-88-INTAKE-MANIFOLD_W0QQitemZ260027778458QQihZ016QQcategoryZ36474QQrdZ1QQcmdZViewItem

[Joe L.]

Re: big block intake manifold

Tim----

Yes, I'm very interested; I'll e-mail you right away.

[Joe L.]

Re: big block intake manifold

Steve-----

Yes, as far as I know the intake plenum center divider height is the only difference between the GM #3933163 and the GM #3933198. With the 3933198 the lower center divider height was a CASTING FEATURE of the manifold, although finish machining may have "obscured" that.

A 3933198 could, therefore, be created from a 3933163 casting by machining down the center divider as part of the FINISH MACHINING operation. When this was done, the last 2 digits of the 3933163 casting number were ground off and replaced by a "98" stamping.

Actually, I'm surprised that the 3933198 casting was ever created. For the small number of these manifolds ever required for PRODUCTION and SERVICE, it would seem like just reducing the height of the center divider through a machining operation to the 3933163 casting would have been the most efficient thing to do. And, we know that it was done this way in many cases because there are so many of these "modified casting number" manifolds around.

[Steve Antonucci]

Re: big block intake manifold

Joe,

Only concern I have is that as of late, I have seen more and more of these
"modified" '163 intakes on eBay. I don't think there were ever that many
to start with. Colvin states this in his "by the Numbers" book as well.
As you must know, it is just too easy to mill the plenum down, grind off the
end digits, stamp in a "98" and VIOLA! An early production, super-rare ZL-1
or L-88 intake. Buy It Now for $850.00

And yes, I am equally surprised that GM ever made the '198 intake. As you
so verified, only the center plenum was different and this change could have
easily been accomplished with a supplimental machining operation. But as you
also know, GM wasted tons of money on short production run parts.

Steve

[Joe L.]

Addendum

Tim-----

Something I forgot to ask. Does your 3933163 manifold have the lower height plenum divider? It's very possible that some 3933198 manifolds were "created" via machining without the re-stamping of the last 2 digits being performed.

[tim sargent]

Re: Addendum

Joe

The 163 intake on late 68 "IT" L-88 engine does not have the cut down plenum.
I have also seen "198" intakes that do not have the cut down plenum.
Is there any flow data to indicate amoung the 069, 198, 163 and 851 intakes
which one flows the best? I suppose actual performance results would depend upon the cam,header,and carb profiles, it just seems the actual runners are very similar in all four cases.
Tim

[Steve Antonucci]

Re: Addendum

Joe & Tim,

I was just thinking about something. I seem to remember reading a post here
early this year ( possibly ) that seemed to indicate that the '198 intake
actually flowed better than the rest. Based on our discussion, this would
not seem to make sense. But, I do remember the post. Whether or not this
supposed better flow has anything to do with the center plenum devider being
cut down is anybody's guess.

I've never seen a '198 with the full height plenum devider as that was cast
in. '163's were full height, '198's were lowered.

Steve

[Joe L.]

Re: Addendum

Tim------

I've never seen a GM #3933198 that didn't have a reduced height plenum divider. In fact, the specification foir the manifold included a reduced height divider. However, the reduced height divider that was a feature of the casting was really only slightly lower than the divider on the 3933163. Most, but perhaps not all, of the 3933198 castings had the divider further reduced in height by machining.

During the 68-69 period, the aluminum big block intake manifolds went through a bunch of what I regard as miniscule changes that did result in casting number changes. Most notable, there were THREE different castings used for 68-69 L-36 Corvette engines. You'd be hard-pressed to discern any difference between these manifolds except for the casting number.

The 3919851 and 3919878 are among the "mystery manifolds" of the rectangular port, square flange configuration. Whether or not they were actually used in PRODUCTION, no one seems to know, for sure. My guess is that they were used for early 1968 applications, although mostly for non-Corvette engines (the only possible Corvette application would have been early 1968 L-88 and since there was only a total of 80 of these made for the ENTIRE model year, it's not too likley that very many, if any, of these manifold castings were ever installed on a Corvette).

I do not know the runner volumes (and, consequent flow potential) for these various manifold castings.

[Joe L.]

Re: Addendum

Steve-----

As far as I know, the only difference between the 3933163 and the 3933198 was the plenum center divider. If there had been some difference with respect to runner volume, then I don't think that GM would have approved the "re-numbering" of the 3933163 manifolds when the divider was machined down. There would be no way to convert a 3933163 to a 3933198 if there was a difference in runner configuration.

I expect that the information regarding the increase in runner volume for the 3933198 comes from folks speculating this based on their belief that the "L-88/ZL-1 just must have had a higher flowing, higher performance manifold". I don't believe that's the case, at all, though.

There is one other difference which may exist between the 3933163 and 3933198 CASTINGS, though. I believe that the 3933163 uses a pressed-in bypass fitting on the front of the manifold whereas the 3933198 uses a threaded type fitting.

[Mark #28455]

198 manifold divider is machined

I have 2 of the 198 manifold with original 1968-69 date codes. In both cases, the center divider is machined out. In addition, I have a 163 manifold with a machined out divider that was likely dealer installed on my L89 as part of an L88 conversion (also date coded early 1969) and the center divider casting appears to have been identical to the 198 intake - the cast septum separating the 2 sides of the plenum is cast just a shade lower than the rest of the carb mounting surface. I have yet been able to identify any difference at all in the casting prior to machining.

Mark