400/350 small blocks

gonner

Member
Jun 12, 2011
55
Gray,Ga
Can someone please show me the differences between the deck of each block. I know the 400 has siamesed cylinders but what does that look like.thanks for the help:bowtie: :bowtie:
 

AJ_72

Veteran Member
Jul 3, 2003
5,129
Chebanse, IL USA
The siamese cylinder bores are just that, siamesed. They're joined together externally, like siamese twins.

Any other SBC has the cylinder walls separated so coolant can pass around them, 360*. The siamesed walls don't allow great circulation, so that's why they put steam holes in the block that go into the head to relieve the build up of air pressure in the crevice between the deck surface and the cylinder walls.

Here's a 350 block, then below it is the 400 block for comparison. You'll see the steam holes (~1/8" IIRC) just below where the two cylinder walls meet.

F20043859.gif


148_0504_how_12_z.jpg
 
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