[GRX]

A lot of talk about block thickness but none of how the molds are structured as of yet. The location of the mold parting lines can have a very significant effect on the "skeletal structure" of the overall casting. The way the mold parts are arranged can also have a very significant effect on strength since it effects how the molten metal flows through the mold when it is poured.

As we all know, the core for these blocks consist of many parts. The mold is not just one big unit but must be made in pieces to allow removal of the casting afterwards, and also to allow for location of extraction pins, hot gas escape ports, etc ... etc ... The resulting lines between the core parts are refered to as the "parting lines", and usually result in a less consistant grain structure in the area.

OK ........ on to some images ............

Here we compare my 1967 400 block to the 1975.

1st image = '75 block. Please note the orientation of the parting line maked red.

2nd image = '67 block. Very different orientation wouldn't you say?

The third image is another view of the '75 parting line. There are many images of later castings which cracked right along that vertical line up to the main cap. The '67-'69 arrangement places the parting line much farther away from the main saddles.