Big block Chevy (BBC) ports are large, the primaries hanging off them are large, and the leverage all of that puts on a flange is why BBC headers crack at the flange weld more than any other platform. A 3/8" plate doesn’t have the section to resist it. This one is 7/16" across the face and 3/4" through the stub, pocket-milled so the mass sits where the load is instead of spread evenly across a part that doesn’t load evenly. Fits conventional BBC heads on 4.84" bore spacing.
Machined From
7/16" flange face — mill-certified 304 stainless billet
3/4" overall thickness at the tube joint, including integrated stub
1/8" deep counterbored tube land on every port
Machining & Finish
Precision CNC machined in-house from solid billet
Pocket-milled profile — material removed where it does no work, kept where it does
Perimeter fillets on all outside corners
100% edge break — every port, every bolt hole, every edge
Precision-skimmed sealing face for flatness across the full gasket plane
Straight from the machine to the box. No secondary deburring, because none is needed.
Options
1/8" NPT EGT bung
O-ring groove for a gasketless seal
Port size and shape — select above
Why it stays flat
A thin flange doesn’t stay flat. Weld heat pulls it, heat cycles keep pulling it, and it cups away from the head until it leaks at the gasket — usually after the header is built, coated, and installed. We machine ours from 7/16" 304 billet with a pocket-milled profile and perimeter fillets so the sealing plane resists distortion from weld heat and repeated heat cycling. It goes on flat and stays flat.
Why the counterbore matters
Every port is counterbored 1/8" deep for a tube land. Your primary drops in, squares itself, and sits at a consistent depth without fixturing or eyeballing. Most shops sell that as a custom-order option. We machine it on every flange we make.
Why every edge is broken
Every port, every bolt hole, every outside corner. Not because it changes how it seals, but because it’s how the part should leave the machine.
Made in-house. Mill-certified material. Short lead times.