Looking under the hood at the Humphrey’s controlled compression engine at a stop in San Francisco on a trip, are (left to right) Ira B. Humphrey of Denver, racing driver Freddie Ababashian, A. Black, a Ford dept. manager and Floyd Leopold, also of Denver. The press photo date is Aug. 22, 1952 and Humphrey is seen describing how his variable compression engine works. The 1949 Oldsmobile is fitted with the standard L-head six with a special cylinder head that has been made to house the system.
This system is fully described in a Popular Science article along with great pictures that gives you its principles of operation and much background information. A quick descript-ion is that it uses engine oil pressure over a spring loaded and regulated piston to keep the combustion pressure per square inch constant through the whole range of engine speeds. The Old Motor photo.