Pontiac Engine Block Identification

Trying to figure out if you have a Pontiac block, which engine size it is, and what it came out of? Pontiac made it easy to identify their engine blocks. The engines were coded with many numbers and letters. The casting code will help determine what the block is. The block code was used to ID what application the engine was to be used for. The date code will show when it was made.

Valley Pan:

If the intake is off, the top of the block should still be covered by a valley pan. All Pontiac engines came with a valley pan. If it’s missing, you’ll need a replacement before bolting an intake back on.


(valley pan being removed)

Even if you buy a remanufactured motor, it should come with the valley pan.



(Note the intake sitting above the valley pan)

Transfer Lug:

The “transfer lug” looks like a small pyramid at the passenger side of the distributor hole. The 389 and 400 blocks will not have this lug. The 326, 350, 421, 428 and 455 blocks will have the transfer lug. This “lug” was used to identify an engine that needed “transferred” to another line for additional machining.

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.


(Pontiac 455 (see the ’55’ in the center of the lifter valley) with the ‘Transfer Lug’)



(Pontiac 400 without the ‘Transfer Lug’)

Freeze Plugs:

There were only (2) freeze plugs in the side of the block from 1955 to 1966. Pontiac began using (3) freeze plugs in the side of the block in 1967.


(Pontiac 455 (‘455’ cast to the left of the first plug) with (3) freeze plugs)


(1961 Pontiac 389 with (2) freeze plugs)

Motor Mounts:

Starting in 1959 with the 389 block, side motor mounts were used with two holes (#2 & #5 below).

In 1964 all blocks had provisions for block mounted starters. Although the full-sized cars still used the bell housing starters.

In 1970, all blocks now had (5) motor mount holes, but not always tapped. The additional holes were done to fit the 2nd generation Firebird/Trans Am frame. The last of the V8’s (1977 to 1979) did not have the rear motor mount holes at all. Making it very difficult to install in to a GTO/Tempest.


1959-1969 Blocks have only (2) motor mount holes on each side of the block (see #2 & #5). These blocks will fit any 1964-1974 Pontiac A-body except cars originally equipped with a 455, which used a 3-bolt style mount. Later cars with 3-bolt motor mounts can be adapted to fit this block using a Butler Performance WRP-MM6 or Ames  Performance N24CCA adapter kit.

1970-1976 Blocks have all (5) bolts holes (see above) but were not always tapped. The additional holes were done to fit the 2nd generation Firebird/Trans Am frame.  These blocks are very interchangeable and will fit any 1959-1979 Pontiac V8 motor mounts.

1977-1979 Blocks have only (3) motor mount holes (see #1, 3 & 4), but can be adapted to fit earlier cars that originally used a 3-bolt mount by using the Butler Performance WRP-MM5 or Ames  Performance N24CC adapter kit.

Date Code:

The date code is cast on the distributor pad. It is a 3 or 4 digit code. The first digit will be a letter:

J=October (September for 1967 model year)
L=December (All years except 1966 (67 model) when the letter M was used)
M=December (1966 Only, for 1967 model year)

Followed by a 1 or 2 digit number for the day of the month. The last digit will be the last digit of the year it was manufactured. 5 could be 1965 or 1975.


(The ‘B205’ indicates that the block was cast on February 20, 1965)

Just in case you’re wondering, The ‘N’ and ‘D’ represents day or night shift. Both of these blocks were made during the day.


(The ‘L42’ indicates that the block was cast on December 4, 1972)

Starting around 1969, Pontiac cast a 2 digit year number next to the distributor also.


(Additional Year Code added starting 1969)


(Block was cast E214 = May 21, 1974)

Casting Code:

All engine blocks have a casting code. This code will tell you the year it was to be used and the displacement. However, these codes were used for more than one year and could have different machining or even different main caps.

  • Casting codes for 1955 to 1963 are found on the passengers side of the block.
  • Casting codes for 1964 to 1967 are found on the distributor pad, except the 421’s.
  • Casting codes from March 1967 to 1981 are found on a ledge just rearward of the number 8 cylinder.


(Casting Code – On passenger side 1955-1963)


(Casting Code – On distributor pad 1964-1966)


(Casting Code – 1967 to end of production)

Check out our Searchable Pontiac V8 Engine Codes Page to see a list of casting numbers and applications, or to search a number you’ve found.

Block Code:

Pontiac engines have a block code. This code doesn’t always match up to a specific year, model, or engine. But if you have the casting date and casting code off of the block, you can generally find what vehicle had all of these codes in common.

Starting in 1965, Pontiac began using a 2 digit letter code. Above the 2 digit code will be the motor unit number, which is either 6 or 7 digits. It is important to note that it is not related to the VIN number. As a general rule, “W” coded blocks are manual transmission and “Y” coded blocks are automatics. And most of the “Z” coded blocks are also auto. The “X” coded blocks are a little of both.

Check out our Searchable Pontiac V8 Engine Codes Page to see a list of Block Codes and applications, or to search a Block Code that you’ve found.



The blocks Unit Number is the sequential production number for the engine. Often referred to in service bulletins to identify production changes or service issues.

Block VIN (Vehicle Identification Number):

From 1955 through early 1967, the block serial number and the VIN were the same. In late 1967 the block VIN was revised. It started out with a 2 (for Pontiac), the last digit of the year and a letter for the assembly plant followed by the last 6 digits of the vehicle VIN. It was located on the front of the block, on the passengers side, at the bottom near the timing cover.

Common assembly plant letters are:

A = Alanta,
B = Baltimore,
C (or S) = Califorina/Southgate,
E = Linden, NJ,
G = Framingham, MA,
K = Kansas City, MO,
L = Van Nuys,
R = Arlington, TX,
X = Kansas City, KN,
Z = Fremont, CA,
1 = Oshawa, Ont.


(This Block VIN indicates 2 = Pontiac /  9 = ’69 or ’79 / G = Framingham, MA / last 6 of cars VIN)

Displacement Identification:

Displacement ID’s were cast in the side of the block starting with the 1968 428. A 428 was cast on the driver’s side near the center between the freeze plugs, and ’28’ was cast in to the lifter valley.

In 1970, the 350 and 455 had their size cast into the block on the driver’s side near the front freeze plug, and a ’50’ or ’55’ cast in to the lifter valley. [you should also look on the opposite side too]

In 1971 and going forward, the 400 also has ‘400’ cast into the block on the driver’s side near the front freeze plug, ’00’ cast in to the lifter valley. [you should also look on the opposite side too]

421 – no 421 numbers located anywhere; look for a square machined area on front passenger side deck where the block meets the head.

389 – no 389 numbers cast any where on the block; look for notch on passenger side deck where the block meets the head.

Block Displacement Numbers in The Lifter Valley:

Often these numbers are missing, especially on 4 bolt main and other performance blocks.

  • 5 / 0 = 350 block
  • 0 / 0 = 400 block
  • 2 / 8 = 428 block
  • 5 / 5 = 455 block
  • X / X = 78-79 blocks


(Pontiac 455 displacement cast on the block)


(’55’ 455 displacement cast in the lifter valley)


(Pontiac 400 casting on the block – Note the ‘XX’ before the ‘400’ – see information below)


(Pontiac 428 casting between the freeze plugs)

The 1978-1979 XX Engine Blocks:

It has been said that the only good block after 1974 was used in the 1978-1979 Trans Am’s with the W72 special performance option. These blocks have ‘XX” cast in to the lifter valley (which otherwise commonly contained the last two digits of engine displacement), next to the block casting code, and on the side of the block.

Pontiac improved on the durability of the 6.6 engine by reviving the 481988 block casting, which was beefier than the 500557 used elsewhere. The large ‘XX’ castings help quickly identify these blocks. The XX-481988 blocks are as durable as any earlier block, and can be considered an excellent choice for performance use.

All of the ‘XX’ blocks appear to have a casting date of 1977. None have been found with a date after November 1977.


(This lifter valley has ‘XX’ cast in to it identifying this as the beefier W72 engine block)


(The ‘XX’ cast above the block casting number identifies this as the beefier W72 engine block)


(‘XX’ cast in the side of the block next to the ‘400’ displacement casting)


(Note the 1974 casting year, but the 1977 casting date and the ‘XX’)

The block above is interesting. Remember that the 481988 casting was brought back, and the last year it was cast was 1974. It appears that they reused that casting, but added the ‘XX’ and changed the dates it was actually cast. This then is actually a 1977 block, not a 1974 block.

What 400 Block Should I Search For?

These are the best Pontiac 400 blocks to build:

9799914 1970 (Ram Air III)
9799915 1970 (Ram Air IV)
481988 1971-1974
481988 XX 1978-1979 (1974 recast in 1977)

Starting in 1975, the Pontiac 400 500557 casting was thinner in certain areas to reduce weight, and roll pins were used in place of dowels for main cap retention.

What 455 Block Should I Search For?

The 1973-1974 455 SD blocks (490132 casting) are no doubt the best 455’s ever made- they have 4-bolt main caps, reinforced lifter valley and main cap saddles. Good luck finding one cheap though- they are highly desirable and sought out by collectors to build service replacement (SR) 455 SD engines for 73-74 SD T/As and Formulas.

The 1970 455 block (9799140 casting) has 4-bolt caps, and is more common, and the 1971 455 HO (483677 casting) also has 4-bolt main caps- both are worth sleeving if you find one that needs repairs or is already bored over .060.

The 1971-1974 455 (485428 casting) is the most common production block- it typically is equipped w/ 2-bolt main caps, but this isn’t a problem, since Pontiac V-8s use good quality, large main cap bolts. Add ARP main cap studs and the 2-bolt main caps can easily handle 600+ hp.