Here's some basic dimensions on the manifold primary runners and merge collector.
Surface area of primary at the head -
3.062" DMP Manifold
2.759" 1 7/8" tube header

Surface area of primary at collector
2.785" DMP manifold 4 ports collectively 11.14" area
8.9416" I.D. Tube header with a 3.5" I.D. pipe 4" O.D.
11.787" I.D. Tube header with a 4" I.D. pipe 4.5" O.D.

Normal tube header runner length is 15.5"
DMP exhaust have a 27" long runner length
Our primaries carry through the riser flange

We can manufacture the riser completely dry or partially dry, which ever you prefer.

As far as ordering, if it's standard exhaust stuff, the website will gain you free ground shipping on orders over 150.00. If it's anything complicated, I'd do it by phone. We're always available to answer technical questions or process orders.

We offer a hard anodize finish for salt water applications. You can order black or silver powdercoat on top of a hard anodized manifold at no additional charge. If you want a candy color finish add $150.00.

Are you making your exhaust system for the "LS2-LS7' motors?? CHEERS AW