C3 '68 TriPower intake casting code stamped

[Ted S.]

I just picked up a '68 TriPower intake 3919850 and the casting code is stamped on a raised block where the normal casting code is. At first I thought maybe it was an early run of the intakes but there is one on ebay that has an earlier casting date on the bottom than mine and it has the numbers cast in. What causes GM to stamp the casting number verses the normal process of the raised casting code?

Here's the one off of ebay and mine has a raised block where the 3919850 is and has the numbers stamped. It even looks like it was stamped ground and re-stamped since there is still a ghost of a couple of the numbers. The ebay one is dated 9.8.67 and mine is dated 12.1?.67 (I can't make out the second day number).

[Joe L.]

Re: C3 '68 TriPower intake casting code stamped

Ted-----

I can't tell you, for sure, why it was done, but I can tell you that the "stamped" casting numbers are seen from time-to-time on original intake manifold castings, especially the aluminum variety.

As you may be aware, there were 2 different L-68 manifolds used for the 1968 model year. These castings were extremely similar and differed in only a few, subtle ways. It may be that by December, 1967 Winters Foundry was already casting the later manifold. However, for some unknown reason, the Tonawanda engine plant may have machined some of these to the earlier design features and, consequently, ground off the later number and stamped on the earlier. More often, what's seen is a case of an earlier number ground off and a later number stamped on. But, it can go either way.

Keep in mind that these numbers were, primarily, placed on the manifold for INTERNAL identification purposes. They were NEVER intended for the purpose of "authenticity" or "counterfeit protection". What was important to GM was that there were certain numbers on the piece for certain reasons. Whether they were cast on or stamped on didn't make a lot of difference (except that it was more labor intensive to stamp them on and that was generally to be avoided).

[Ted S.]

Re: C3 '68 TriPower intake casting code stamped

Thanks Joe, That makes sense. The interesting part on this manifold is the area is a raised pad in the same place and about the same height/length of the casting numbers. So rather than an early version of the 3919850 this is probably a late version of it. My understanding from Colvin's book is the difference between the 3919850 and the 3937795 is the depth of the coil mount boss threading. In this case maybe since a change over was coming, and it was machining change only, they put the raised pad on the mold and then stamped the the "identification" number at the time of machining. Or possibly they had a couple of lines doing the machining and they hadn't completed the switch over. Thanks again for the insight.