ZL1 Corvette at Auction Next Month.

[rynoshark]

Over the last few 3-4 years, a trove of significant documents were discovered in GM's Heritage Center on the ZL1 development program and RPO ZL1 production. These completely changed the discussions on 1969 Corvette ZL1 and clarified many things due to new facts being uncovered.

There were only two RPO ZL1s, as confirmed by Corvette records. There MAY have been other Corvettes with a ZL1 engine that escaped the factory somehow, but only two RPO ZL1s (thus sometimes you hear about "more" than 2 ZL1s from the factory...which there may have been, but there were only 2 RPO ZL1s). The first RPO ZL1 was confirmed in Corvette/GM paperwork at the Heritage Center as having been built on December 9, 1968 when parts were first used (ZL1 alu engine, ZL1 console badge). The document timelines appear to indicate the first RPO ZL1 was built with an M40. The second RPO ZL1 (Daytona Yellow) is well documented, so we know exactly the bookend period for the entire RPO ZL1 production. Even more important, we know that any early RPO ZL1s built in 1968 had to be built with closed chamber heads, as per GM documentation.

Important information from other threads on CorvetteForum, Yenko, and Supercar Registry:

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https://www.corvetteforum.com/forums...post1602874168

The great news for us Corvette enthusiasts and historians is that a number of documents related directly to development and production of the L88 and ZL1 have been uncovered within GM's Heritage Center. These were created by Chevrolet executives in 1968 and 1969, with exact dates, and paint a fairly clear picture of the timeline for ZL1 production. Many myths, hearsay and foggy memories have been passed down for decades, much of which is not backed up by actual facts or data (and, in some cases, are at odds with GM records).

Summary of key findings:
* per November 21, 1968 memo the L88 variants (including ZL1) were to be built ONLY with closed-chamber heads, effective November 26, 1968, until the open-chamber head was available (which is also noted on this document as not until late March 1969) [Notice of Production Change C69-299]
* on December 9, 1968 the "427 CUBIC INCHES ZL1” console badge (part 3958746) released and was first available on that date in St Louis for installation in production cars [Notice of Production Change C69-39]
* on December 9, 1968, the M40 automatic transmission parts released and was first available in St Louis on that date for production of the RPO ZL1 option [Notice of Production Change C69-39, Supplement 1]
* on or within days of December 9 1968, the first RPO ZL1 rolled off the St Louis plant assembly line [Notice of Production Change C69-39, Supplement 1]
* on August 1, 1969 the RPO option ZL1 was officially cancelled for the 1970 model year, and the aluminum ZL1 engine would only be offered as a service assembly [Corvette Engineering Center memo]

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https://www.corvetteforum.com/forums...post1602871908

Per annotations on Chevrolet's internal NPC "Notice of Production Change C69-39" documentation, the first date that a ZL1 engine assembly was available for production installation at the St. Louis Corvette assembly plant for a Corvette with option RPO ZL1 was December 9, 1968.

Further, the separate internal Chevrolet document "Notice of Production Change C69-39, Supplement 1" indicates with annotations that the first day parts were available for building a Corvette with a M40 automatic option for RPO ZL1 was also December 9, 1968.

In the absence of any other internal Chevrolet documentation, the data from these NPC documents indicate it appears that on—or within days—of December 9th, 1968 the first Corvette with option "RPO ZL1" was built. Further, based on this documentation, any Corvette built prior to that date which may have had an aluminum ZL1 type engine installed would not have been with the "RPO ZL1" option code. Given the Daytona Yellow ZL1 is well documented to have been built in September 1969, these would be the two bookend RPO ZL1s.

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https://www.yenko.net/forum/showpost...6&postcount=41

The internal GM documents indicated that "12-9-68" was the first "parts availability" date for an RPO ZL1 engine available at St. Louis plant for installation into a production Corvette. From what I understand, GM did not leave rare engines sitting around to be installed sometime well into the future, thus these documents seem to indicate the first RPO ZL1 was built on or slightly after 12/9/1968 given documentation shows that the Daytona Yellow ZL1 was definitely a RPO ZL1 and it was built in September 1969.

An additional important discovery in internal GM documents found at GM Heritage Center was that the type L88-engines were actually built with closed-chamber, despite the original CEC engineering plan for them to be open chamber (which was what appeared in various magazines in period). However, a "Stop Order" was placed on the open-chamber L88/ZL1 engine due to problems with the aluminum cylinder heads, which extended the closed-chamber models (including IT L88) for the 1969 model year way beyond the original engineering timeline. I don't have the data in front of me, but I believe this stop order was lifted sometime in the March 1969 timeframe, likely coinciding with the Camaro ZL1 engines released for "production" COPO 9050 Camaros starting with chassis #3. The first two "red hot" COPO Camaro ZL1s were requested by Pete Estes to ship out by December 31, 1968, for homologation/racing purposes and were not "customer" cars. As this was a production engine reliability issue for the ZL1, the lifting an engine stop order would probably have applied to Corvettes and Camaros at roughly the same time.