Abstract: A cast cylinder head for a reciprocating-piston i.c. engine is formed with helical inlet ports at least 50% of the internal surface area of each of which is afforded by a machined surface or surfaces. Each such port may be formed in two machining operations, in one of which the inlet duct is machined and in the other of which the bowl is formed with a cylindrical lower portion and a hemispherical upper portion. A recess may be machined in a third operation in one side of the bowl. The inlet duct may be lined by a liner sleeve at least over its inner end portion, the inner end of the sleeve protruding into the bowl as a swirl barrier. Alternatively the port may be formed asymmetrically by numerically-controlled machining, a barrier lip being formed as a part of the machining operation.