Abstract: A cylinder head for an internal combustion engine includes a helical inlet port with a sharp edge swirl lip on a generally cylindrical valve stem recess. The helical inlet port has an inlet passage, a bowl-shaped chamber which has a rim that terminates in an annular valve seat and which encompasses an annular space about a generally cylindrical valve stem guide for a poppet valve stem. One surface of the bowl meets one wall of the inlet passage along a swirl edge, which has a radius of less than about 0.5 mm, and preferably a sharp edge with a radius of less than about 0.1 mm. Such swirl edges may be formed by casting the inlet port with excess material, which is then machined away only within the bowl along a cylindrical cutting line.

Abstract: A cylinder head for an internal combustion engine of the reciprocating piston type includes a helical inlet port with a flat wall portion in a section of the port upstream of a bowl-shaped recess about a valve stem guide. The flat walled section meets a generally cylindrical portion of the recess adjacent a cusp-shaped swirl edge. The orientation of the flat portion with respect to a reference feature, such as the axis of the valve stem guide, may then be used as a measure of the accuracy of casting of the inlet port, and may also be altered if so desired to vary the swirl characteristics of the inlet port.