For the most part weakest point in a block
is in the center of the cyl.. I have cracked
3 blocks(all SB) and they tend to crack near
mid way down the bores.. that is generally
the weakest area in the block... if you do a
1/2 fill you strengthen the block to the middle
of the bores.. in a stock block the thinnest
part of a block is the cyl walls(its about .200
thick if its a decent block) so with a 1/2 fill
you strengthen to that point(about 1/2 way down)
then you have the top of the deck.. they are
thick so if you didnt fill you would have the
total cyl area that can be weaker.. if you fill
you are reducing the weak area and shortening
the area above the fill.. it can add rigidity
to the whole block(depends on design) but most
blocks are fairly solid in the bottom end.. IMO
it wont help correct cracking the bottom
end.. to me that is another issue... this is
just my opinion... I have both filled and not
filled.. if a street car use a oil cooler.. as
said your taking away the heat transfer when
you fill