How to identify Pontiac engine blocks

Pontiac blocks are interesting power plants that are often misunderstood and improperly identified by sellers and buyers alike. The blocks of all Pontiac V-8s from the 287 to the 455 are the same size and very close to the same weight, which can make it more difficult to identify the 11 different engine displacements produced from 1955–79. Adding to the confusion, multiple block codes were used, and date codes can overlap up to three decades.

The truth is, however, Pontiac V-8s are relatively easy to identify if you know some of the outward clues. So as we get ready to work on our next Redline Rebuild engine time-lapse with a mid-1960s Pontiac 389 V-8, I dove into these power mills and their ground-pounding torque, which made them top contenders of the ’60s and ’70s muscle car wars.

Motor out of a 1965 Pontiac GTO Tri Power
Motor out of a 1965 Pontiac GTO Tri Power Reggie Horning
1970 Pontiac 400 V8 with #13 Ram Air Heads and Firebird Ram Air Exhaust Manifolds
1970 Pontiac 400 V8 with #13 Ram Air Heads and Firebird Ram Air Exhaust Manifolds Reggie Horning

Whether the engine is sitting in a car, on a stand, or on the floor, at first glance you will note that all Pontiac blocks have a hydraulic lifter valley pan. That simply means that the intake is not sealed to the lifter valley, allowing you to remove the intake while the engine remains sealed. The distributor is located at the rear of the motor and can remain installed when the intake is removed. This is where you will find your first clue of the engine’s age: If the valley pan has the PCV port at the rear, the block is from 1966 or older, and if the port is at the front, it is 1967 and newer. Of course, the valley can be easily changed or missing, so you’ll need to pry further.

All Pontiac blocks from 1964 and up have the same provisions for mounting the transmission, starter, and engine. Prior blocks had the starter mounted to the transmission bellhousing, and large-body cars, like Bonnevilles and Catalinas, continued to have the starter mounted in the transmission bellhousing until 1965 (despite having the provision for starters on the block in 1964).

Further inspection of the block and freeze plugs will yield more clues to the block’s age. Pontiac blocks have two different freeze-plug configurations. Blocks cast from 1955–66 have two freeze plugs while the 1967–78 blocks have three freeze plugs. Once done there, go ahead and inspect the driver’s side of the block.

As you look there you may find a pretty simple clue that will end your engine identifying search. On 1968–69 428 blocks you will find “428” stamped between the freeze plugs. On blocks produced in 1970 and after, you will find 350, 400, or 455 stamped towards the left side of the front of the block. There is no displacement stamp for 421, 389 or 326 blocks.

Pontiac Date Code on the Cylinder head
Pontiac Date Code on the Cylinder head Reggie Horning
Pontiac Engine Casting Number
Engine Casting Number Reggie Horning

To further identify the year and application, move to the top and rear of the block, where the distributor is mounted. Here you will find the date code and block casting number. The date code is a three- or four-digit code that always starts with a letter, which represents the month the block was cast (A = January, B = February, C = March, and so on through L = December). It should be noted that for the 1967 model year, Pontiac used M for December.

The month is then followed by one or two digits, which represent the day the block was cast, followed by one more digit, which represents the year. For example, a block stamped “J129” was cast October 12, 1959, 1969, or 1979. Armed with the previous clues, you can pin the year down. If the block is stamped with a 350, 400, or 455, it was likely cast in 1969, because GM (as discussed) started stamping the displacement on the block for the 1970 model year. Also, all blocks cast in 1969 and later have the last two digits of the year here as well. So if you see “70” stamped in this area, the block is a 1970. If not, we can look for further clues to fully identify the block and application. If you are trying to confirm a numbers-matching block for your car, we will need to go a little further regardless.

Example of 400 cast in block
Example of 400 cast in block Reggie Horning

Casting codes can shed more light on identifying the block, matching codes to identify the displacement and year used. It is important to note, however, that casting codes were often used for more than one year and could have different main caps or machining depending on the year. On 1955–63 blocks, the casting code is on the passenger side of the block. For 1964–67, they are found on the distributor pad. Casting codes for 1968–81 appear on the ledge at the rear of the block behind cylinder eight. Once you locate the casting code, you can find your block through a number of searchable databases. We’ve found the Wallace Racing website to be particularly helpful and accurate.

At this point we can move forward to the front of the block where the codes are stamped, just under the passenger-side cylinder head. Pontiac started using these two-digit codes beginning in 1955. It’s important to note that Pontiac re-used the codes for different years and applications, so you need to know the year of your block to correctly identify the code. Again, you can visit any number of searchable databases online or refer to a Vintage Chilton’s Manual for year, make, and model, which will also list the codes. As a rule, “W” code blocks match with manual transmissions, and “Y” and “Z” code blocks are automatics. The “X” code blocks are a mix of both.

Above the code is the block unit number, and the common line of thought is that this number matches the last six digits of the VIN, as with other GM applications. However, when it comes to Pontiac, this is simply the engine sequential number, generally referred to in service bulletins for updates in production. (The VIN is located on the passenger’s side front of the block, down where the timing cover and the oil pan meet.) From 1955 until early 1967, the block unit number represented the last digits of the VIN of the vehicle that the motor was originally installed in. Late in 1967, the number 2 was added at the beginning to represent Pontiac, followed by a digit that indicated the last number of the model year (such as “9” for 1969) and a letter that represented the originating assembly plant. These digits were followed by the last 6 digits of the VIN.

Photo of VIN on the front of the block
Photo of VIN on the front of the block Reggie Horning

Also consider the casting codes on the heads. These are cast into the center exhaust ports, which you can again reference on several sites. The date code is cast to the right of the cylinder head code, just below the valve cover.

Cylinder head casting on Cylinder head
Cylinder head casting on Cylinder head Reggie Horning

We could go into a lot detail about other components and various casting numbers for intakes, exhaust manifolds, and more. However, these are all searchable online or can be found in Mark Allen’s booklet, Pontiac V8 Engines Factory Casting Number and Code Guide 1955–81, which is available on Amazon or eBay.

If you are out shopping for an engine or checking out a car and want to identify the motor as correct or complete, keep in mind that the engine and major component casting dates should be within a day or two. The date codes should also pre-date the vehicle build date by a few days to several months, depending on the assembly plant location. For example, if your car was built at Pontiac, the component casting dates are likely to be very close to the vehicle build date, but a Fremont-built car will likely have a bigger gap (typically several weeks) between the component casting dates and the vehicle assembly date. This is because all Pontiac V-8s were assembled at Plant 9 in Pontiac, Michigan, and then shipped to the assembly plants.

As with any purchase, be sure to do your homework before you buy. It’s a good idea to come armed not only with your phone to search the internet, but with reference books, too, in case you can’t get a signal. Don’t be afraid to bring a knowledgeable friend along, as well as a few cans of brake cleaner, an old toothbrush, and some rags to help you clean and positively identify those numbers. Happy hunting!

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    Thank you for the information. Did Pontiac have the 428ci. available to the 1966 GTO? If so, what would the code(s) look like? My 66 GTO has a 350ci in it. I bought it that way as a kid. I want to replace it with a 1966 GTO engine; the 389 or the possible 428. Thoughts? Thank you again

    No they weren’t due to the top brass keeping the reins on Delorian but you could order a dealer installed 428 if you knew how. I do restoration and any Firebird or GTO i do gets either a 428 or 421 one depending on the year and if it has an original engine, that goes with it on an engine stand.

    Neighbour’s found a wrecked car in the woods. It is apparently from the 30’s its a flathead straight 6 .the engine is extremely solid, looks rebuildable. I have a casting #498686(?) On the head. The pontiac Indian head symbol is visible on the side of the block . I have pictures, but I don’t know how to post them to my comment. Any information would be appreciated. Thanks

    Yes it will! Contact Ames Performance Engineering, they have a kit to facilitate the engine swap.

    1969 canadian Pontiac 427
    block T0205LE
    Heads 3931063
    how many were made also what is the value of that motor not touch 90,000 miles with turbo 400 transmission

    It will if it had the Pontiac 400 engine to begin with. If not you will need motor mounts to fit the engine your installing (3 bolt) mount. Be sure to get your headers in there before you bolt her down. Better to install transmission on. It will have so much power you won’t even need the accelerator pedal. Except for the freeway.

    I have a Pontiac block stamped GME where the displacement code normally goes. It has a 4 bolt main and a Steel crank. The heads that where next to it when I found it are 670s, but I don’t know if they are the originals. I believe the block is a 428 but I am not positive. Any thought appreciated.

    Im trying to identify my block it has a date code of B241 and has an engine size of 400 stamped on the drivers side toward the front, from this I think it is a 71′ 400. but on the passenger side it is stamped with GM1. did GM make the blocks in 71?

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