I recently engaged in a discussion on Bring A Trailer about identifying the originality of Pontiac’s last high-performance 400-ci—the T/A 6.6—in a 1979 Trans Am that was up for auction. That then got me thinking. Many Pontiac enthusiasts are familiar with the T/A 6.6 and its optional availability on 1977-1979 Firebirds (and 1977 Can Am), but some may be uncertain in determining if the numbers-matching engine remains with that car. What makes that difficult, you might ask? In my years documenting such examples, I found a few factors that could create confusion in identifying Pontiac’s last 400s (not just limited to T/A 6.6) and I’d like to share those with you, but let’s cover some basics first.
Developed for the 1977 Trans Am, the T/A 6.6 was Pontiac’s response to Corvette’s L82 engine option. Why the Corvette when the Z-28 was Trans Am’s closest competitor, you might ask? After Chevrolet dropped its Z-28 for 1975, Pontiac took aim at dethroning the Corvette. The high-performance 400-ci was rated at 200 hp in 1977 and 220 hp in 1978-1979. (Photo courtesy of General Motors)
Most are aware that to identify an engine’s original application Pontiac stamped the face of its V-8 blocks with a two- or three-character code. Depending upon the model year, that code could note such specifics as displacement, transmission type, cylinder head variances, camshaft selection, carburetor and distributor settings, etc. For instance, in 1974 the “YY” stamping indicated an L75 455 4-barrel with automatic transmission while “W8” indicated a Super Duty 455 with manual transmission—the components of each vary greatly.
Pontiac typically stamped the face of its V-8 blocks with a two- or three-character engine application code and an Engine Serial Number (or ESN). The location of each can vary by model year and/or era. This image is characteristic of Pontiac blocks from the mid-1960s to the mid-1970s.
Pontiac also stamped onto the face of its V-8 block a 6-or 7-digit (depending upon the model year) numeric sequence. This Engine Serial Number (or ESN), Engine Unit Number (or EUN), or Motor Unit Number (or MUN)—all synonymous terms—is a particular engine’s sequential build number during a given model year. The ESN was stamped at Pontiac’s Engine Assembly Plant (Plant 9) and used to identify specific breakpoints or ranges for such things as assembly issues or engine component changes. The ESN does not have any correlation to the original recipient vehicle’s VIN, however.
Since the mid-1960s, Pontiac positioned its V-8 ESNs above the engine application code. That practice was revised for the 1977 model year, which—like that shown here—otherwise left that area blank.
With the 1977 model year Pontiac no longer stamped an ESN onto its V-8 blocks. Instead, the ESN was printed onto a stick-on label that was placed on the passenger side valve cover. While the sticker was suitable for short term identification, the labels often became illegible, tattered, or simply fell off as miles accumulated and/or time passed. Today, very few labels remain on such Pontiacs and those that do reside on well-preserved vehicles with low mileage. Fortunately, ESNs of this era have little significance to the general hobby, so a missing label (or unknown ESN) is of no real concern.
Remnants of the stick-on label that originally contained a printed ESN is sometimes present on the passenger side valve cover in original, low-mile Pontiac V-8s such as this 1979 301-ci.
Generally, of great concern to Pontiac hobbyists is driveline originality, which can directly reflect value. The term “numbers matching” typically refers to a block’s VIN stamp matching that of the vehicle it resides in. Beginning in 1968, federal law required that automakers permanently stamp the original recipient vehicle’s VIN upon its primary driveline components (engine and transmission) to thwart theft. Pontiac instructed its vehicle assembly plants to apply a nine-character stamping containing the last eight characters of the VIN onto the block face in an area adjacent to the timing cover. We learned over the years, however, that the exact location of this partial VIN could vary by assembly plant.
Per federal requirement for 1968 model year vehicles, Pontiac instructed its assembly plants to stamp each engine with a nine-character code that began with a “2” (signifying Pontiac) followed by the last eight characters of the VIN of the vehicle it was originally installed into. This diagram—commonly found in vintage Pontiac vehicle assembly manuals—illustrates where Pontiac wanted the partial VIN stamp located.
The GM assembly plant in Norwood, Ohio produced second-gen Firebirds for its entire 12 model year run. The GM assembly plant in Van Nuys, California supplemented second-gen Firebird production in 1970 and 1971, and then again from 1978 to 1981. The partial VIN stamp on Pontiac V-8s in Norwood-built Firebirds is generally found in its prescribed location. However, the block’s partial VIN stamp in later Van Nuys-built cars is generally much higher, oftentimes in an area just beneath the cylinder head flange.
Workers at the Norwood, Ohio assembly plant—evident by the “N” as the third character of this sequence—typically located the partial VIN stamp on Pontiac V-8s in its intended location.
By the late-1970s, Pontiac’s V-8 architecture—which was originally introduced in 1955—had become dated. Keeping the larger-cube V-8s emissions complaint with (the seemingly ever-increasing) new standards was a daunting task for Pontiac’s engineers. Meanwhile, to achieve increasing fuel economy standards the industry trend was toward smaller (and lighter weight) vehicles powered by small displacement V-8s. With less demand for larger-cube V-8s, Pontiac couldn’t justify investing the resources required for modernization. It decided to develop the specialized 301-ci and discontinue its 455-inch V-8 after the 1976 model year, its 350-inch V-8 after the 1977 model year, and its 400-inch V-8 after the 1978 model year.
Pontiac planned to celebrate Trans Am’s tenth anniversary in 1979 by producing a limited-edition silver-themed model and it included a traditional 400-inch Pontiac engine under hood. Since the 400 would no longer be in production during the 1979 the model year, Pontiac assembled and stockpiled several thousand T/A 6.6 engines during the 1978 model year for use in 1979 Firebirds. Not all T/A 6.6 engines went into Tenth Anniversary Trans Ams, however. Only 1,817 such examples were built. In total, the high performance 400-ci was installed into 8,693 1979 Firebirds (367 Formulas and 8,326 Trans Ams).
The 1978 model year marked the end of the line for traditional Pontiac V-8 production. Several thousand 1978 T/A 6.6 engines were stockpiled for use in 1979 Firebirds. How could Pontiac not offer a 400-inch V-8 in its highly publicized 1979 Tenth Anniversary Trans Am? (Photo courtesy of General Motors)
To determine if a specific 1978 or 1979 Firebird is equipped with its original 400-inch Pontiac V-8, we must first identify in which plant it was assembled and the VIN’s 7th character denotes it—Norwood-built cars will contain an “N” while Van Nuys-built cars will contain an “L.” Once known, we can then explore the general plant-specific areas on the block’s face where the partial VIN stamp should be located. It may be obscured by a buildup of grime or under layers of paint, but with bright lighting and possibly some elbow grease, a series of 9 characters should appear—and if original to that car, the last eight characters will mirror the vehicle’s VIN!
Firebird volume had grown so significantly by the late-1970s that Norwood couldn’t keep up with demand. The Van Nuys assembly plant began supplementing Firebird production in 1978. Workers at that plant—evident by the “L” as the third character in the sequence—applied the partial VIN stamp on Pontiac V-8s in areas that differ from the practice at Norwood. Sometimes it was just left of the application code as shown here.
It’s worth noting that I have documented a handful of original 1978 and 1979 Firebirds whose T/A 6.6 engine is void of its federally-required partial VIN stamp. We can’t immediately assume the block in such examples is incorrect or a service-replacement unit replaced under warranty. While that’s certainly possible, it’s my opinion that if everything else about the block (such as its XX481988 casting number and its casting date in within the range of the last known casting run) and the other bolt-on equipment (such as the carburetor, intake manifold, and cylinder heads) appears in order, it’s quite likely that the unstamped block is original to that Firebird and might be considered an assembly line anomaly. The burden might then be on a potential naysayer to prove otherwise. I must admit, however, I consider these very rare examples exceptions to the rule.
Other times, Van Nuys workers applied the partial VIN stamp above the engine application code stamping where the ESN formerly was located. I’ve even seen examples where careless workers applied the partial VIN stamp directly over the engine application code greatly obscuring both!
Hopefully, the next time you or someone you know asks how to go about determining if their 1978 or 1979 Firebird retains its original 400-inch Pontiac V-8, the information presented here can save you (or a potential buyer) time and headache. And maybe even from a bad investment!
A reader shared with me this interesting example where the partial VIN on the block of this Van Nuys-built 1979 Trans Am is stamped upside down.
Have you seen any interesting anomalies in your years of documenting Pontiac V-8s?