Stock gaskets, eh? That 400 came from the factory with NO gasket between head and exhaust manifold. Two machined surfaces seal well enough. Probably saved $2.00 per engine.

But the gaskets that come in rebuild kits are probably what you mean. IF the header has a flange to bolt against, it won't matter if the gasket overhangs the port. What may give problems is if the header flange only overlaps the exhaust port by 1/8". You could be experiencing this.

It may be possible to move the header around a little bit to center it and have more even overlap of the gasketing surfaces.


R.