Valve Cover / Breather Configuration

[Gearhead999]

The crankcase needs to breath. If you think about the piston movement, it displaces just as much air on the down stroke as it does during exhaust and compression. This air has to go somewhere. So you end up with a positive pressure in the crankcase. You also, depending on age/wear, have some blowby, pressure getting by the rings, mixed in there too.

The PCV should be put in the vacumn hose going to the intake/carb port. Then you still need an intake so the system balances and has a good flow through the crankcase at all times. That is usually done with a hose going to the air cleaner assy.

The PCV is there incase of a backfire. It will shut off the flame from igniting the fumes in the oil pan. It also meters, by the orfice size, the amount of scavanging the vacumn is providing.

Don't see how PCV will effect engine running rich. But, if you seal the motor up, no PCV and no breather caps you usually end up blowing out a valve cover or intake end gaskets.

I run filler cap with hose to air cleaner and right valve cover with PCV to vacumn. I have also ran the filler cap vented without hose, but then when engine is run hard you'll get oil misting out of the breather cap onto valve cover. Without the PCV and just caps you'll also get some oil fumes/odor at times, which offends somepeople.

You can also run, two or four breather caps one or two on each valve cover. These will mist though because many performance valve covers don't have baffles or they've been removed to clear valve train. Some run them on extensions that will cut down on misting. Some add baffles to the extensions which cuts down misting further.