That’s what I was thinking.

I did a bunch of testing on that stuff 8-10 years ago.
As Russ said, the stock intake is really a cork.

Stock 906 head @.500 lift = 226cfm
Bolt on stock intake manifold = 189cfm
Mild clean up stock intake = 195cfm
Mild clean up 6bbl intake = 217cfm

Mild ported 346 head @.500 lift = 259cfm
With stock intake = 202cfm
Mild clean up stock intake = 212cfm
Mild clean up 6bbl intake = 242cfm
Gasket matched RB M1 single plane = 255cfm

The stock head with the cleaned up 6bbl intake outflows the ported head with the cleaned up 4bbl intake.