Ported X head 340 header size?

1 5/8 circle area = 2.07 sq in
x 4 = 8.28 sq. in. (One side)
3 in circle = 7.08 sq. in ( one collector)
1 5/8 headers already have more volume than the collectors and your still going to
squash it in to 2 1/2" exhaust pipes on the street.
...but if your racing it would be different through open headers, and who knows what
happens when the exhaust hits atmospheric air pressure after 35 inches?