Block Identification

 

Pontiac blocks are easy to identify if you know what to look for. It is simple, for example, to visually categorize all 1959-and-later blocks into 389/400 or non-389/400. All displacements other than 389/400 possess a “transfer lug” (found at the rear of the block shaped like a “mountian” or “pyramid”). There are only two exceptions: the 1961-62 421 SD (the same blank casting as the 389) and the 1973 SD-455. All V8 blocks cast prior to 1959 (287, 316, 347, and 370) were “standard” displacement and did not have a transfer lug. In addition, these 1955-58 blocks did not use side-mounted motor mounts as did all blocks from 1959 forward. All blocks through model year 1963 have a production number cast into the passenger side of the block. The casting number for these blocks are as follows:

 

1955 (287 c.i.d.) #518037 1956 (316 c.i.d.) #521560 1957 (347 c.i.d.) #523293 1958 (370 c.i.d.) #528456 1959 (389 c.i.d.) #532000 1960 (389 c.i.d.) #536387 1961 (389 c.i.d.) #538181

1961 (421 SD) #538181 1962 (389 c.i.d.) #538181 1962 (421 SD) #538181 1963 (326 c.i.d.) #548211 1963 (389 c.i.d.) #543680 1963 (421 c.i.d.) #544988

 

Beginning with the 1959 389 c.i.d. blocks, side motor mounts were utilized for the first time. Two motor mount holes appear on each side of the block, a feature that would continue through 1969. Beginning in 1964, all blocks were cast with provisions for block-mounted starters, even though most of the large cars still used the bellhousing-mounted starters. The block casting number location moved from the side to the distributor pad (except for the 421s). All the blocks cast through model year 1964 included cylinder head stud oiling passages. No engines after 1964 utilized the stud-oiled heads, so these passages were eliminated in 1965. All blocks from 1955-66 used two freeze plugs per side. Block casting numbers for the 1964-66 engines are as follows:

1964 (326 c.i.d.) #9773153 1964 (389 c.i.d.) #9773155 1964 (421 c.i.d.) #9773157 1965 (326 c.i.d.) #9778840 1965 (389 c.i.d.) #9778789

1965 (421 c.i.d.) #9778791 1966 (326 c.i.d.) #9778840 1966 (389 c.i.d.) #9778789 1966 (421 c.i.d.) #9778791 early 1966 (421 c.i.d.) #9782611 late

 

All blocks are cast with a date of production code. This code appears on the distributor pad. The code consists of a letter, followed by two or three digits. The letter signifies the month (A = January, etc.). The letter “L” signifies December for all years but calendar 1966 (1967 model) when the letter “M” was used for December. Since “I” was used in all years, it is possible that both “I” and “J” were used to designate September. The reason is not known. The 2nd character in sequence (or 2nd and 3rd if three digits appear) is the day of the month. The last digit designates the year of production (not necessarily the model year). For example:

A #9773155 block with a date code of J23 = October 2, 1963.
A #9782611 block with a date code of F126 = June 12, 1966.

All blocks produced for model year 1967 were recast for three freeze plugs per side. Beginning in mid-1967, the block casting number changed location from the distributor pad to the rear of the block, just behind the #8 cylinder. The foundry line casting can be found in two places, on the front side of the block (GM1, GM2, GM3, etc.) and at the extreme rear end of the block on the distributor pad (1, 2, 3, etc.). In addition, 1968-69 428s received two additional displacement identifiers, a cast “428” on the side, and a “28” cast into the center lifter valley rib. Similar identifiers would be used to identify other displacements (455, 350 in 1970, and 400 in 1971). Casting numbers for the 1967-69 blocks are as follows:

 

1967 (326 c.i.d.) #9786339 1967 (400 c.i.d.) #9786133 1967 (428 c.i.d.) #9786135 1968 (350 c.i.d.) #9790079 1968 (400 c.i.d.) #9790071 1968 (400 RA) #9792506 1968 (428 c.i.d.) #9792968

1969 (350 c.i.d.) #9790079 1969 (400 c.i.d.) #9790071 1969(400 RA IV) #9792506 1969 (428 c.i.d.) #9792968 1969 (303 c.i.d.) #546313 1969 (400 RA V) #9792968 1969 (400 RA V) #545887

 

NOTE: All 1967-68 428s are 4-bolt. All 1969 428s have 4-bolt holes, but low-performance engines with #46 heads have 2-bolt caps. All 1968-69 #9792506 Ram Air 400 blocks have 4-bolt caps.

In 1970, all blocks received three additional motor mount holes for possible mounting in the new Firebird chassis. In some cases, only three holes were tapped, but five pads were machined. Blank block castings for 1970-76 are as follows:

1970 (350 c.i.d.) #9799916 1970 (400 c.i.d.) #9799914 1970 (400 RA III) #9799914 1970 (400 RA IV) #979991(5) 1970 (400 RA V) #481708 1970 (455 c.i.d.) #9799140 1971 (350 c.i.d.) #481990 1971 (400 c.i.d.) #481988 1971 (455 H.O.) #483677 1971 (455 c.i.d./late H.O.) #485428 1972 (350 c.i.d.) #481990 1972 (366 c.i.d.) #(485)212 1972 (400 c.i.d.) #481988 1972 (455 c.i.d.) #485428 1973 (350 c.i.d.) #488986

1973 (400 c.i.d.) #481988 1973 (455 c.i.d.) #485428 1973 (455-SD) #(490)132 1974 (350 c.i.d.) #488986 1974 (400 c.i.d.) #481988 1974 (455 c.i.d.) #485428 1974 (455-SD) #(490)132 1975 (350 c.i.d.) #488986 1975 (400 c.i.d.) #488986 early 1975 (400 c.i.d.) #500557 late 1975 (455 c.i.d.) #500813 1976 (350 c.i.d.) #488986 1976 (400 c.i.d.) #500557 1976 (455 c.i.d.) #500813

 

The block date code is found just to the left of the distributor hole at the back of the block. This can make it difficult to read if the engine is installed in the car. This code (B059) breaks down as February 5, 1969.

The block casting number on mid ‘67-and-later blocks is found just behind the #8 cylinder on the passenger side of the block. This number, 9792968, denotes a 1969 428. The number is located next to the distributor hole on earlier engines.

 

 

Non-389/400 engines featured an identification or transfer lug on the rear passenger side of the block. The exceptions to this were the 1961-62 421 Super Duty, and the 1973 455 Super Duty engines.

 

Many of Pontiac’s 2-bolt main engines, most notably the lower-performance 428s (1969) and 455s (1970-and-later), were drilled and tapped for 4-bolt caps from the factory.

 

Along with the displacements cast into the side of the block, additional identifiers were added to the lifter valley ribs as well. “28” denotes this as a 428, while “55” would reflect a 455 and “00” a 400.

Displacement identifiers for the 350 began in 1970, while all 1971-and-later 400s received the treatment.

Pontiac began casting displacements in the sides of the block (among other places) in the late ‘60s. This practice started with the 428s in 1968. 455s received the identifiers in 1970 when they replaced the 428s.

 

FYI: In 1977, only the 350 and 400 c.i.d. engines remained. A new 301 Pontiac short deck engine joined the line-up along with some other “corporate engines”, such as the Olds 403 and the Chevy 305. The Pontiac 400 block was cast with revised motor mount bosses, and will only mount in late Firebirds or Grand Prixs. The blank casting number for the 1977-79 400 is #568557. The 301 can easily be recognized by the lateral oil filter location. In other words, the 301 oil filter sticks straight out, unlike other Pontiac blocks which are attached to a housing that aims the oil filter downward.

A wide variety of specific engine/trans codes are stamped into the front of production blocks. Trans codes may appear to conflict. Prior to 1965 (the start of the “two letter” system) the two digit engine code, which was the last two digits of the full six or seven digit part number, was stamped followed by the standard trans code. An optional trans code, if installed in the vehicle, appears nearby, often on top of the other characters. Most production blocks, except 1964-66 and most 1967s, received a vehicle identification (V.I.N.) stamp. Prior to 1964, the block V.I.N. was identical to the actual vehicle code. Beginning in late 1967, block V.I.N.s appeared with the digit “2” designating a “Pontiac” engine, followed by the year, a letter identifying the assembly plant, and the vehicle serial number.

A researcher familiar with the various assembly plant code letters can sometimes ascertain whether a block was originally installed in a Firebird or a GTO. Lordstown (U), Norwood (N), and Van Nuys (L) built Firebirds, but not Tempests. A block V.I.N. of 29L123456 would indicate that the block was originally installed in a Firebird built at Van Nuys, CA.