There has been some discussion lately about oil bath vs. paper air filters and also of the merits of full flow oil filtering. I have been researching what was being published in the 50s and 60s regarding these topics. One of the more relevent papers was "Engine wear as affected by air and oil filters" by W.S. James and B.G Brown published in 1950 in the SAE Journal.
To paraphrase some of the conclusions:
1) The causes of engine wear can be quantified.
2) Some oil wetted air cleaners provide almost no protection against airborne dust.
3) An oil bath air cleaner will reduce ring and bore wear to 1/10 that of some oil wetted type.
4) Although the oil bath air cleaner exhibits the same flow efficiency as the 'disposable cartridge', the 'disposable cartridge' type showed a marked reduction in engine wear of the rings (1/4 to 1/5) and cylinder bore (1/2). There was also a reduction in the loss of weight of the bearings. This is with oil filter.
5) The 'pull-over' of an oil bath air cleaner may reduce engine life by several times. Pull-over being when the accumulation of dirt raises the air cleaner oil level such that dirty oil is drawn into the engine. See here for a definition of pull-over:
http://www.hastingsmfg.com/ServiceTips/air_intake_filters.htm 6) Using an oil filter will reduce bearing wear by 50% or more.
7) Chrome plated top rings double the time that an engine can be operated before excessive blow by occurs and will reduce bore wear by ~75%.
5) Changine from metal mesh to filtered crankcase breather will not materially affect ring/ bore wear but will decrease bearing clearance increase by better than a third. This is without an oil filter.
It would seem that Chevrolet's oil wetted metal mesh air filters, lack of oil filter, and no crankcase air filtering was about as far from good engineering practices as you could get.
