[LMSRACER]

This Measurement is made across the Main Webbing at the Base of the Cylinder Bore. This area is just past the Cylinder Bore and is actually machined larger than the cylinder bore.



Results:
1) 1967 400 = 0.222"
2) 1971 400 = 0.185"
3) 1972 455 = 0.145"

Clear Winner = 1967 400
NOTE:
This Block also has some of the Thickest Cylinder Walls of ANY Pontiac Block that I have ever Sonic Tested.

This is where the 1967 400 Shines in My Mind.

Also, keep in mind that the Casting Lines in these 400 Blocks do not run up into the Dowel Pin Area of the Block the way that the 455 does.

So, along those lines of thinking, the 1967 400 is Probably the "Least Likely" 400 Block to Bust the Main Webbing out of the Block. (Through the Dowel Pin Area) Although, I don't see any reason to believe that it wouldn't be just as prone to Cracking down the Center (Up Through the Cam Bearing Oil Hole) as the 1971 400 Cast #481988 that I checked.

In Fact the Oil Hole that's Drilled from the Main Bearing Saddle to the Cam Tunnel to Supply Oil to the Cam Bearings is also Different between these two 400 Blocks.

Both Blocks have an 11/32" Oil Supply Hole that Steps down to a 5/16" Hole before the Passage Reaches the Cam Tunnel/Bearing. What's Different is that the 1967 has an 11/32" Hole with a Depth of 2.125" while the 1971 has the same 11/32" Hole, but it only has a "Drilled Depth" of 1.425" before it Transitions to the 5/16" Hole/Passage.

All that means is that there is a little more meat in that particular area on the 1971 Block Casting.

Next I'll point out what I meant when I said "Undercut" as it pertains to the 400 Castings.

Larry S.