My guide to sourcing the correct exhaust gaskets for a classic engine, because the wrong gasket creates a leak that eventually becomes an exhaust valve problem.

The gasket must match the port shape. A round gasket on a D-port head seals the center and leaks at the corners. A D-port gasket on a round-port head seals the perimeter and flows poorly in the center. Both situations create exhaust leaks under load.

For high-performance applications with headers, the connection at the head is the most critical. A steel exhaust gasket used with header flanges that are not perfectly flat will leak. The correct approach: resurface the header flange, use a quality exhaust gasket, torque properly, and re-torque after the first heat cycle.