Breathers are not emission legal and the engine does need to breath to compensate for pumping motion in the engine. Be sensitive not to overfill the engine oil.
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I had the terminology wrong, as
Blown7 noted I should have said "
air/oil separator" - can you guys re-comment on the necessity/advantages/disadvantages of adding an oil separator.
A seperator should not be required. Race cars want the best conditioned air to make power an use seperators in their dry sump systems.