Which head ?

[Bob Culver]

It is probably all on the Internet somewhere, but the Ricardo squish patent was regarded as the saviour of the s.v head, it continuing in some cars to the 1960s at least (Ford Pop, small Studebaker) In the very early 1920s cr for larger motors was only 4:1 or so, limited by pinging. The Ricardo head generally enabled 5:1 which represented a big gain in economy. The early RR Silver Ghost was 3.2:1! To the 1950s at modest rpm many sv engines approached ohv in output  (A40, Minx 100E Ford, Minors) etc) When cr reaches about 7:1 the breathing of a sv head becomes a major limitation. To not speed combustion too much and/or avoid patents, many sv heads did not adopt a fully flush squish area.