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Distinguishing a Pontiac Engine Block
Here's some helpful information on how to identify that block you're examining.

All Pontiac blocks have a hydraulic lifter valley pan. The distributor hole is located on the rear deck of the block which allows for the easy intake removal without disturbing the distributor. While most Pontiac motors were painted blue, metallic blue or robin's egg blue, color is only one of many clues and not one that can be relied upon to determine the Pontiac line. You have to do more looking and verifying to be certain.

Freeze plugs provide more clues

Some Pontiac blocks have 2 large freeze plugs and some have 3 on each side of the block. Early blocks, those from inception through 1966 had 2. Pontiac engine blocks cast in 1967 through the last casting in 1978 have 3 freeze plugs on each side.

Motor mount holes

Ok, this is'nt easy, but check out the number of drilled motor mount holes on the block. Pontiac blocks with only 2 bolts holes per side were cast before 1970. 1964 to 1969 Pontiacs engines were all 2-hole blocks. Blocks cast in 1970 to the last of the run had 5 holes per side, at least in theory. Some blocks, like this 400 that's in a 79 TA 6.6, is different (below left). It is a 3-holer with two blank pads (no holes). These pads can be drilled and tapped if necessary to accommodate a different engine mount. The other earlier block (to the right) is a 5-hole block. These are all drilled and tapped.

Block displacement

350/400/455---displacement numbers cast into block on driver's side near the front freeze plug [you should also look on the opposite side too--check photo]

428---located on driver's side near the center between the freeze plugs

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.

Year of the block

At the rear of the engine at the top near the distributor hole can be found the important casting numbers that reveal the year of manufacture. The fourth digit indicates the year of the casting. So, if you have examined the rest of the block, you can easily ascertain the year the block was manufactured. The other info in the string may be helpful, but is not usually too relevant. The first letter, could be A through L, signifies the month. A=Jan, B=Feb, and so on. After the letter are two digits; 01=1, 25=25. Remember the last digit is the year (0-9).

Locating the engine code

There's really no way you can accurately determine the year of the engine by merely knowing the engine code. You have to put all the information together to be certain. Pontiac used two-letter engine codes in different years in various cars. In later years, Pontiac added a corresponding VIN number to the block. Whatever the case, you need to examine the front passenger side of the motor. If the VINs match, that determines the engine option from the factory. Look to see what's there. Pontiac engines began including VINs on blocks as early as late 1967. The first digit identifies the GM division. The number 2 = Pontiac. The second digit represents the year of the block. The third digit represents the assembly plant...the last digits match the sequence number of the car's VIN.

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