Ok, so I am not an expert on this. But my understanding - which may be right or wrong -

Fact: the Chevy V8 was designed in the early 1950s. First was the 4.4 liter version in 1955.

Guess: It was probably designed for about 5,000 rpm tops.

To spin faster with later versions, say as with the 5.0 liter of 1967 that revved to (supposedly) over 6,000 rpm, they added 4-bolt mains to keep the flex of the crankshaft under control.

In no way does this mean the original design was "bad", only that it was not designed for high-rpm usage. Previous to the 4-bolt mains Chevy smallblocks put out more torque but didn't use 4-bolt main.

So I think torque is not the factor, it is RPM.

Wikipedia also states it is related to flex at high RPM: wikipedia: 4-bolt main


Now the Nissan VG v6 was designed from the ground up as a "high" rpm engine (6,000 being high back in the 1980s). So it doesn't need "upgrades" to spin up. NO FAIR to compare 1950's designs to 1980's designs.