For proper sealing the embossment (raised seal) should match the opening of the header, the head port is of secondary concern since it is most often smaller than the header opening. Please see the illustration above. SCE introduced the first embossed copper exhaust gaskets in 1995, and they are still the best way to seal even warped or pitted exhaust manifold or header sealing surfaces. Copper is malleable so the gasket conforms to surface irregularities filling in leak paths, unlike multi layer steel which is too hard for all but the smoothest surfaces. In house design, tooling and manufacture insure superior quality gaskets for the widest array of applications. Whether on your tow vehicle, motor home, hot rod or race car, a properly fitted SCE Pro Copper exhaust gasket will form a permanent trouble free seal.