Valve Cover / Breather Configuration

[David Fulford]

I have been told several different stories about how many/what kind etc breathers I should have on my valve covers. I was looking for some advice or different opinions. Right now I have one breather with a hose from the valve cover to the large vacuum port on the back of the intake manifold (this one has an in-line PCV valve because it wouldn't pass inspection a while back without one ????) and one breather with a hose from the other valve cover to the air cleaner. Do I even need either one of these; any help would be appreciated

The motor is a iron head crate motor, Weiand intake, Holley carb, MSD,
standard bells and whistles.

Thanks.

[bmxmon]

I run two pcv valves, one in each of my valve covers running to my carb. Not sure if its "correct", but works for me.

[David Fulford]

I'm not sure what exactly is correct either. My car runs great but has always ran rich, no matter what carb (Holley 600) adjustments I make. Someone told me that if I did away with the breathers, it would force the motor to suck more air through the carb and maybe help the richness problem. It sounds good in theory to me but I really don't know and am afraid to start tinkering with it because it does run good as is. But it runs so rich that it burns your eyes after being started anywhere near the garage. I think I am going to try a new carb in the near future and hopefully help the richness problem.

Thanks man.

David Fulford

[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.