[AMC-list] Freeze plugs/ Casting plugs

[David Crooks <david.crooks@xxxxxxxxxxxx>]

No matter if die cast, or sand cast, you still need cooling passages inside
the block, which means the cast mold has to keep the casting material
out of those area's.  So any casting mold is not only shaped like the
outside of an engine, but also all the internal water cooling parts as 
well.  and of course, the internal parts need to be aligned with the external
shape, so what the "freeze plug" holes really are is the supports for the
internal structure of the mold (ie the water passages).

The internal bits of the cast will always be expendable,   you have to 
be able to wash them out afterwards.  Die casting, where the outside parts
are heavy steel, allows you to pump the casting material in under 
pressure, instead of letting gravity do the work, but that doesn't change
the need for a removable internal core of sand, or whatever material.

FWIW, an aluminum alloy with 12% silicon is an eutectic alloy!  
One of it's advantages is that it will transition from a liquid to a sold
almost instantaneously, which helps with manufacturing.  All those
Hyper-eutectic pistons you've been reading about, well that means 
they have more than 12% silicon.

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