Yup, that was then, this is now.

Chevrolet gave the rights to Yenko to purchase ZL-1 blocks from the Winters Foundry in Canton Ohio. (with some restrictions).

The part number listed is 3952318

The letter is dated June 7 , 1974

signed by F. A. Duco , Director, Manufacturing Sales

Chevrolet produced other, different; aluminum big block castings that were not part of the ZL-1 program. Some were never sold to the public, provided to Chaparral and McLaren for their race cars. As of early 1968, they began development of an 'aluminum block L-88' that later became Corvette RPO ZL-1 for the 1969 MY. Due to poor sales, the ZL-1 program ended July 1969.

Chevrolet continued to develop aluminum big block castings for racing without liners or provision for a mechanical fuel pump. These were sold as bare blocks only, never used in production. Those and Yenko blocks are not considered ZL-1s.

The only true ZL-1 castings are 3946052 and 3946053, as used in 2 production Corvettes and 69 Camaros.

looking at the Yenko documents it looks like they bought about 200 of the ZL-1 blocks from the Winters Foundry after 1974.

These were required by SCCA for the Corvettes that ran the ZL-1 engine.

The other Yenko aluminum blocks were not legal to race in the SCCA Corvettes at that time.

Zora and Vince Piggins were involved with getting the blocks made.

The part number 3946052 is listed as the "cylinder and case rough "

The part number 3952318 is for the "cylinder and case assembly "

The 3952318 assembly has a parts list of about 20 parts including bearing caps and bolts, plugs, dowel pins , cam plate, and other small parts.

These Yenko documents are in the Mark Gillespie 2nd Yenko Era book. Includes a hand written note from Vince Piggins.

Do you know if those had YENKO cast into them?

Seen a few like that, one did not have coolant passages.

The Yenko ZL-1 blocks did not have the Yenko name on them.

On the Winters invoice the ZL-1 blocks have a note - (no trade name)

The Yenko blocks have a note - (with Yenko name plate)

There are photos of two blocks , one has the Winters snowflake and the other block has the letters "YENKO" in the same place where the snow flake is on the other block.

Did the 1969 ZL-1 blocks have a date code like an iron block?
The ZL-1 blocks that Yenko had made would be after 1974 but not sure if they had a date code on them.

There are letters back and forth with Bill Porterfield with an agreement to use and promote the Yenko block. dated Dec 1978 . I know Bill had a company called Mid Engineering and built a mid engine 1978 Olds 442 and a Kelmart GT using Olds engines but may have also used the Yenko block.

Yes, near the motor mount on the left side. ZL-1 blocks have a casting sequence number, a machining sequence number.

I have a small log of data on blocks that abruptly stops as of July 1969. Have not seen a later casting. They did a pilot run of ZL-1 blocks in the late '80s but used a different, darker alloy. A few of these blocks were machined and built. Somewhere I have a pic of unmachined blocks on a pallet.

Too bad, the entire ZL-1 story may never be told.

Yenko and Greenwood and others were still using the ZL-1 block in the 1970s for SCCA racing.

I remember an article on Greenwood showing about 15 blocks he had bought from Chevy. There must not have been many new blocks left by the mid 1970s.

Reason to believe Winters cast just under 600 blocks. Engine production eventually totaled 182: 80 "ME", 14 "MG", 54 "ML", and 34 "MM". I have heard there was a high scrap rate but no hard numbers. No matter, plenty of unused blocks around.

Another observation: have never seen and do not know of a CE ZL-1 short or fitted block. The ZL-1 Camaros I know of that had warranty engine failures were either repaired or had complete engine replacement with a converted ME code engine.

At this time, I do not know of a production ZL-1 Camaro built with a Holley #4296 carb. Some of Gibb's 50 were retrofitted; original owner history on one of the last cars built stated it was delivered with the L72/L78 #4346.