Exh manifolds in an Early A...
The 273 and 318 have smaller ports. Attached you can see a 318 gasket (blue one) behind a 360 magnum/340 gasket. You can clearly see daylight around the corner edges. But some FABO members have managed to get the 318 gasket to seal on a magnum/340 manifold. I swapped out my '69 318 heads for some swirl port heads to make sure that I got a good seal and to get the flow that comes with the magnum heads/ports.
The 273 and 318 have smaller ports. Attached you can see a 318 gasket (blue one) behind a 360 magnum/340 gasket. You can clearly see daylight around the corner edges. But some FABO members have managed to get the 318 gasket to seal on a magnum/340 manifold. I swapped out my '69 318 heads for some swirl port heads to make sure that I got a good seal and to get the flow that comes with the magnum heads/ports.