Virtual, Let's talk about the evolution of the oil filter. Since they were introduced in the 1920's (on Packard I believe), they started as a BYPASS filter. The first application as a FULL FLOW filter on a passinger car was on the 1946 CHRYSLER as a result of the Chrysler 6 cyl. engine having been used in tandum in a WWII tank. From that point, new engine designs almost always included a FULL FLOW filter. The exception is the Small block Chevy of 1955 which had a BYPASS filter on the new 265 cu. in. engine for one year only. You can tell a '55 Chevy at a car show has the original engine if the filter is sitting up on top. By 1956-57 FULL FLOW filters were pretty much the standard. Remember, 1950 was when the first API Standards, ML-MM-MS and DG-DM-DS were issued governing the standards of motor oils. Later, circa 1960, API changed to the SA- SB----to-- SM that we now know. The compression ignition engine oils follow a similar succesion. Don't forget that in the 1940's the 1k OCI was the norm. I believe Kendall was the first refiner to promote "KENDALL: THE 2000 MILE OIL". Engine designs required tighter tolerances, higher speeds and longer service life. The progression of filters and oils followed through R&D and here we are today with engines going 250+ k with few problems. Air filtration is a story for another time. FWIW--Oldtommy
