Intake manifold volume

One of the subjects that keeps coming up is which manifold to use for what purpose.

I was surfing, looking for info on another subject when I came across this from Nascar, showing intake manifold volumes.
http://nascarheads.com/chevy_18_sb2.html

We choose heads by intake runner volume, why shouldn't we choose intake manifolds by volume????? Inquiring minds need to know. :HMMM:

I always try to view the intake manifold as an extension of the cylinder heads.
The whole idea again is to have the great flow numbers with the smallest intake volume.