Back in September I wrote about how documentation was the must-have option when buying a classic Corvette. That article focused on mostly the paper trail: dealer invoices, build sheets and tank stickers. Today the focus is on the engine and the clues available for verifying authenticity. While the term “Matching Numbers” in its simplist form is various serial numbers and codes located on key parts and their relationship to a particular year of Corvette, it’s the engine block that is the most important part of the matching numbers equation. Unfortunately, as Corvette values rise, so do your chances of buying a Corvette with altered numbers being passed off as an original. As my favorite mantra goes when purchasing a Corvette, knowledge is power, and the more you can learn about documenting a Corvette prior to purchase, the less likely you will get burned with buying a Corvette of questionable lineage.
A series of codes and stamps are located on the engine block that will allow you to identify it as being manufactured specifically for a Corvette. There are dates of manufacture and the engine’s original application if you just know where to look. As the year’s progressed and engine options increased, the numbering and casting system obviously changed and became more specific. For the examples provided, I will be referring to the 327 ci 300 hp small block V8 in my 1966 Corvette.
The casting number is a sequence consisting of raised numbers that was cast into the engine block when it was made. What’s a bit tricky here is that casting numbers on Corvette blocks can also be found on other engine blocks made by GM. Casting Numbers are important to the engine documentation process because certain numbers were used for Corvettes and some were not. Also, the numbers are specific to the size of engine in the Corvette. 283′s, 327′s and 427′s all had their own casting numbers specific to individual years, so for the process of documenting a Corvette engine, the casting number will be used to confirm that that block was used in a Corvette and that it was available during the same year the Corvette was manufactured, and finally, it was unique to a specific engine size. The casting number on Chevy V8′s is located on the drivers side of the engine where the block is connected to the bellhousing. It can be a bit hard to see with the ignition shielding in place but the numbers are fairly large. The casting number on my 1966 is 3858174 which is identified as a 327 ci V8 block. That block casting number was also used in 1964-67 passenger cars including the Chevelle and Camaro as well as Chevrolet trucks.
The cast date symbolizes the date of manufacture of the block. Dates are coded beginning with a letter representing the month. Letters began with “A” for January through “L” for December. The next section of digits represents the day of the month and is either 1 or 2 digits in length. The final single digit represents the year. Corvette casting dates only show the single digit for the year. If the block contains two digits for the year, then it was a block manufactured at the Tonawanda engine plant and therefore is not a Corvette block (Corvette engines were almost exclusively built in Flint, Michigan). Cast dates on small block V8′s can be found on the passenger side of flange where the block is connected to the bellhousing. I found this number difficult to locate. On 1965-67 big blocks, the cast date is located on the passenger side of the block where the starter is attached. The cast date on the block in my 1966 is “E 5 6″, which decoded stands for May 5, 1966. If you are trying to document an engine, the casting number would confirm the size of the engine and its intended recipient, and the date code would confirm that the block was used in Corvettes.
Engine stampings evolved in the early years of the Chevrolet V8 engine. In 1955-56, it was simply a continuous serial number, but one that didn’t match the serial number of the Corvette. It was then followed with F for Flint, where the Corvette engine was manufactured and then the year (F55 or F56). The final two letters indicated the original application of the engine. Application Codes usually indicated engine size, type of fuel delivery (Injection or carburetion) and transmission. As engine options grew, so did the number of application suffix codes. In 1957, the serial number was dropped and instead the stamp contained the letter F for Flint, a three to four number sequence for month and day of assembly and then the two letter engine suffix code. Beginning in 1960 the stamp included the serial number of the car it was installed in. The 327 engine in my Corvette contains the following number sequences: 6122891 F0518HE. Decoded, the first sequence is 6 for the year (66) and then the VIN sequence of 122891. The second stamp decodes F for the Flint Plant, May 18 is the engine assembly date and the HE suffix code stands for a 327 ci 300 hp with a manual transmission.
So there you have the basics of decoding engine numbers for the purpose of documentation. Please note that there are some exceptions to the information contained above. In 1965 it is said that there was a shortage of 327 blocks from the Flint plant, so Chevrolet used some engine blocks from Tonawanda. Those engines would have a T instead of F on the stamp, as well as the full year in the cast date. There are several publications that contain a breakdown of engine codes and sequences. The NCRS also provides a publication that details how engines were stamped and therefore, may help you identify restamped engines.