head gasket

The gasket should be as small as possible, while not letting the fire ring overhang the chamfer on the top of the bore. This cut's down on the dead space between the head and block when the gasket is larger than the bore. (A common problem on 318 and 273 builds). Most small block gaskets are made for the largest overbore possible, plus some chamfer, which means they are about 4.180 bore, but not perfectly round.