Chevy 250 - Breather or Cap

[vince1]

I think the breather may have been originally put on to vent excessive blow by out. Probably the cap came in with better emissions standards whereby they wanted all the blow by to go through the combustion process again.

[geezer#99]

Originally Posted by vince1

I think the breather may have been originally put on to vent excessive blow by out. Probably the cap came in with better emissions standards whereby they wanted all the blow by to go through the combustion process again.

The mid fifties and later motors had breathers to allow air in, even before the pcv was introduced. The old road draft tubes needed air into the motor too work.
Older 235's and the 216's before that had baffle slots in the top of the valve cover to let air in.
And fwiw the tube off the side of some valve covers was so a tube could hook from it to the air cleaner. It wasn't a true emissions thing.
Fresh air in, crap air out.
We'd still be running those old systems if we didn't have the government emissions requirements and if people didn't complain about that smell from their motor.