OK, so a 400 isn't a progression of a 350, but a 350 is a progression from the small journal SBCs? I mean, weren't they a good 70-80cid smaller?

 

From the 1955 265 cube SBC thru the LT1, the engine architecture is basically the same. Sure the LT1 has reverse cooling, Opti and a few other changes, but the basic block and head design are the same.

Every time the bore changed the internal cores for the water passages were changed; a 3.75 OEM bore has about the same cylinder wall thickness as a 4.00 OEM bore, and also the 4.125 bore of the 400. While you can retrofit many SBC internals into a 265 ('55-'56) engine, boring it to 4.00 would not work, just like boring a 4.00 OEM bore SBC to 4.125 won't work.

IMO, Ed Cole and the guys that designed the original SBC in the early 50s never envisioned it being stretched to 400 cubes. However, doing this in production was relatively cheap. New internal cores for the larger cylinders with siamezed walls, and larger main bearing bores. A crank is a crank in OEM. Tooling is adjusted for different bearing sizes and stroke. No huge expenses here. Same thing for shorter (400) rods.

The 400 is not just a progression of the 350, it's a progression of the original 265. Not until the LS1 was there a major architecture change.

My $.02

 

That's what I was trying to say

 

"400 is a progression of the 350 and 289 "? yes

"400 is a bored and stroked 350"? naw.

BTW, if anyone really wants to dig into the differences of the small-journal, 350, and 400 SBC engines, John Lingenfelter did a nice little write-up in his book "How to Hot Rod and SBC". Good reading for us young'ins that weren't around when GM was fiddling with block variations.