Block identification other

September 6, 2013 BlockEngine

Welcome to the Pontiac Heaven Parts guide page

  I’m just getting started here, we will start with identifying blocks.  Trying to id something by numbers can be accurate but, it time consuming.  Get to know some of the basic differences between Pontiac parts to become more fluent.


The below pic on the left show an early (1955-60) block on the left, and a 1963 -70 block on the right.  Note-  some ’63 and most 64 blocks had a starter provision even though they did not use it ( except in ’64 Tempest Lemans 326 and ’64 GTO).  By 1965 all Pontiac V-8s used a block mounted starter. 

2nd pic below is of the same blocks but, shows the side view.  You can see that the block on the left has no motor mount holes which makes it a 1955-58 block as 1959 was the first year for side motor mounts.  Note-  early blocks have the strengthening rib that runs the length of the block shown below.  Pontiac discontinued this feature during the 1960 year with exception of some of the high performance blocks.  Also, the oil filter boss was moved further away from the crank centerline.  This is important to know if you want to build a dragster, funny car or altered as this gives more clearance.   

There are always exceptions to any rule and Pontiac blocks are no exception.   However, this information is accurate for engines installed in chassis during assembly.  Over the counter replacement blocks have been known to have addition features like mount bosses, etc.  Most replacement or over the counter blocks will not have vin number and related stampings.  Many will have ‘sr’ stamped on them marking them as service replacement.  Others have no markings or stampings at all.   The block on the right is a 1963-5 and shows the 2 hole motor mount holes.  These motor mount holes were used on all sizes from 1959 through 1969.



Starting in 1970 ( see lower left picture) , Pontiac went to a 5 motor mount hole configuration.  This lasted until sometime in the 1976 model year.  The 3 extra holes were added, the 2 earlier ones were retained making 1970-76 blocks the easiest to swap into other chassis. The lower right picture shows the later 1976-81 3 mount hole pattern.  these blocks are more difficult to install into pre-1970 chassis ( and some ’71-’74 chassis) as they do not have the earlier mount holes.  Some blocks, as the block in the center shows, does retain at least one of the casting bosses for the holes and, thus, could be drilled and tapped but, many blocks do not have this feature.  Fortunately, there are adaptors available for this swap if needed.  Also, the displacement is clearly cast into the side of the block by 1970 and later.  Some earlier blocks also have the displacement cast but, not many.  The far right pic shows a 301 or 265.  Easily recognized by a single freeze plug and horizontal oil filter mount. Further, 265s have ‘265’ cast on the block in several places.