66 L72 convertible

[Allen Murray]

Can someone explain the relationship between the engine block/heads/intake casting date in relation to the engine assembly date, in relation to the body assembly date.

Obviously the engine parts were cast first, then the engine assembled and front pad stamped, then insalled in a assembled body. I would like to know how much time generally passed between each step, and what would be generally considered "correct".

Thanks

[Joe L.]

Re: 66 L72 convertible

Allen------

Under NCRS and NCCB judging rules, 6 months from the various engine cast components casting dates to vehicle assembly date are allowed.

For small blocks, the TYPICAL period between engine component casting dates and engine assembly date was usually in the range of about 2 to 20 days. A TYPICAL span between engine assembly date and vehicle assembly date was about 21-45 days.

For big blocks, there is more variation, especially in the cast dates to engine assembly dates. I've never figured out why. For Tonawanda at the time, the foundry and engine plant were co-located. So, the transit time between foundry and engine plant was, theoretically, nil. Nevertheless, one often sees fairly lengthy spans between component casting and engine assembly. This may have had to do with some sort of "batch build" protocol on the part of the foundry and/or the engine plant. Big blocks were always manufactured in MUCH smaller numbers than small blocks, so there may have been some efficiency in "batch build".

The time for engine build to vehicle assembly was ABOUT the same as for small blocks and perhaps a little longer.

The biggest factor in variance for both big blocks and small blocks was the time that the engine remained in the engine storage bay at St. Louis. Typically, the engine plants shipped the engines out to the vehicle assembly plants just about as fast as they were built. There was not a lot of "warehousing" of engines at the engine plants. However, once they got to St. Louis, they were stored in the appropriate engine bay. IT WAS NOT A FIRST-IN, FIRST-OUT sort of system; the stock was not rotated. So, an engine might sit in the rear of the engine bay for quite awhile and later-received (and dated) engines pulled out for use on the assembly line.

[Allen Murray]

Re: 66 L72 convertible

Joe,

Thank you for the very informative response. I have a '66 L72 engine missing intake. As a look for a replacement how close should the casting dates be to the heads and block? Also,the front of engine pad is stamped T0608XX (June , I have not found the casting dates on the block and heads yet (engine is at a friends house, doesn't know where to look)but could I assume that it will be betwee 2 and 20 days prior to June 8? Is it possible that this engine could have came in an early '67 assuming it sat around for a few months (August?) and used in the '67?

Allen

[Joe L.]

Re: 66 L72 convertible

Allen-----

The L-72 aluminum manifold was not cast at Tonawanda but rather at an outside supplier, Winters Foundry of Canton, OH. Dates on this manifold are usually a moot point since the dates are usually found on the underside of the manifold where they will never be seen.

If the block is a 3869942 casting dated as you say, it is theoretically possible that it could have been used on an early 1967. I doubt it, but it's possible. Of course, if that did happen, the engine suffix code should be that for a 1967 and not a 1966.

[Allen Murray]

Re: 66 L72 convertible

Thanks Joe (The Guru), it is a 3869942 block, not sure of the suffix, I'll have to check. Which brings me to my final question...I have an intake #3933163 which according to my book is '68-69 L78 or '68-69 L72 COPO. I cannot find a casting date on it anywhere, top or underneath, and it doesn't have the snowflake cast on it like other manifolds I've seen. Whats the deal with that?

Allen

[Joe L.]

Re: 66 L72 convertible

Allen-----

The GM #3933163 manifold was manufactured for MANY years. In fact, it was manufactured from 1968 until just a few years ago. In the last several years of its manufacture, beginning about 1995, or so, and continuing until it was discontinued a few years ago, the vendor supplying the castings and, possibly, also performing the final machining, was changed from Winters to some other. At this time, the Winters "snowflake" disappeared. Some other minor features of the manifold changed, too, with the change in manufacturer. So, I expect that what you're looking at is a post-1995 version of the manifold.

From a FUNCTIONAL perspective, the 3933163 manifold will work perfectly in place of the 1966 L-72 manifold. In fact, it replaced the L-72 manifold for SERVICE.

[Allen Murray]

Re: 66 L72 convertible

Thanks again Joe, I suspected it might be a later service replacement. I might run it, but since its not quite correct, I may run just my LS6 manifold which I understand is one of the best performing BB manifolds GM made. Thanks for the help.

Allen

[Joe L.]

Re: 66 L72 convertible

Allen-----

The LS-6 manifold may not perform quite as well as the 3933163. The LS-6 manifold is a very low rise design and was primarily intended to clear low hood profiles (alhough it was also used on many 1970-71 Chevelles and Camaros that didn't really need this low of a hood.