Jim/GA
Well-known member
Roller lifters. They are a newer design, compared to flat lifters. They roll up the cam profile instead of sliding like flat lifters. Hardly any friction, compared to sliding. Having the lifter roll up the cam allows the cam designer to use a very aggressive cam profile, if they want, and not have to worry about cam wear from sliding up that steep ramp.
More importantly, you can use a very strong valve spring and know that the roller lifter can handle the load. The strong spring allows the engine to run at higher RPM and still have the valves close properly (not "float").
Here's an example (not for a Model A):
https://www.crower.com/media/catalo...1e35df139433887a97daa66f/6/6/66292-16_1_7.jpg
TBN is "Total Base Number". Generally speaking, the higher an oil's total base number, the better its ability to neutralize contaminants such as combustion by-products and acidic materials in the oil that would attack metals in the engine, like the babbitt.
Without a PCV system, the Model a has a lot of contaminants in the oil.
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