Durango_Boy

Okay, I got to thinking today. I have seen engines with no PCV valve and no breather, and I have seen engines with a PCV valve and a breather...but I have never seen an engine with a PCV valve and NO breather.

With just a PCV valve and no breather, would the valve do anything? Would it cause problems, or would it act as though there were no valve at all?

yellow 72

Positive Crankcase Ventilation
In order to ventilate you need to replace the removed contaminated crankcase gases via a filtered fresh air intake AKA a breather.

stev5ko

I dont have a pcv either on my 68 with nom 350. It seems to weep oil from both breathers. My prob could also be valve seals but I think I need pcv.

Durango_Boy

Exactly, so what I was wondering, is since there is no vent to allow fresh air in, does the PCV valve actually remove contaminated gasses at all and is the PCV valve rendered useless without the breather?

wrc69v

PCV valve is needed to resurculate the gas fumes that collect in the crankcase system and reintroduce them into the engine where they are burned and disposed of. If you don't run a PCV you will probably smell a lot of gas ata red light.
A breather is needed for reasons mentioned above, to evacuate high pressure from the crankcase oiling system. I highly recomend both. If you are getting a lot of oil splatter look into a breather that screws onto or locks onto the valve cover, you can also run a closed breather that has a hose fitting to dump excess oil into a catch can.
Good Luck!

Durango_Boy

Yeah I understand it's important to have both. I have a functioning PCV and breather, and I run PCV systems on all of my projects. I fully understand the benefits of the PCV system.

The reason I brought this all up is because this weekend I saw an engine with only a PCV valve, but a sealed engine oil fill cap on the opposite valve cover instead of a breather.

This to me seemed wrong. Why have a PCV valve with no way to introduce fresh air into the system. That's why I asked is the PCV valve was rendered useless without the breather.

fauxrs2

I would say effectivly - yes

lars

The breather actually operates in 2 modes:

1. When the engine is operating under light load and manifold vacuum is high, the PCV pulls crankcase vapors out of the crankcase while the breather allows fresh air to enter the crankcase. This is the whole pupose of the ventilation system. It also keeps a slighty lower-than-atmospheric pressure on the crankcase which aids in ring sealing, leak prevention, and power production.
2. When the engine is at WOT, there is no manifold vacuum, and ring blowby is at its highest. Under this condition, excessive crankcase pressure and vapor is allowed to reverse its flow, and it vents out through the breather rather than air being pulled in through the breather. This prevents over-pressurization of the crankcase, since the PCV will not flow enough volume in reverse to handle ring blowby at WOT.

Bottom line is that the breather is required for the PCV to operate properly and to prevent pressurization of the crankcase at WOT.

Lars

Durango_Boy

Thanks Lars. That's what I thought.

mrvette

INteresting topic in that I have been playing with smog pumps and smaller pulleys, using one from a Ford with a Caddy 5" pulley on my '88 vette serp drive setup, getting one hose from each valve cover, into the suck side, and just venting the ouput to under the car....noisey critter, but the crankcase runs at between 5-10" of vacuum....
slightly higher when cold....still running tests and maybe need a oil separator with drain down to the pan...another project....

it's a new Kludge setup right now...but it works....

supposed to be worth some THRITY FIVE HP on a dyno....that is a LOT....IF I save say 15 hp at 2500 rpm cruise, out of the 60 or so needed to drive the car, that's about 15-20% less throttle I need....

wrc69v

Im glad we are all on the same page!
I feel bad for the guy with no breather when he turn 5 grand and blows a gasket.....

stev5ko

Hey Matt,

Not trying to jack your thread but how do I install a pcv system?
Do I plum both vavle covers and where do I route the pcv hose to?

Thanks!

zwede

Lars got it right (as usual). One additional thing:

The PCV air circulation also removes condensation from inside the engine. If you only have a PCV valve and no breather there is very little circulation so condensation builds up inside the engine. Not good.

agent kronus

is it ok to have just breathers on both rocker covers, and no pvc??

cheers

dave

Durango_Boy

Not hijacking at all. It's a good subject that everyone should read to educate themselves...including me for sure.

Yeah the PCV system is easy. It's probably easier to find a set of valve covers that have the holes, instead of making them. The driver's side gets the PCV valve and the passenger side gets the breather. The vacuum line to the PCV valve comes from the carb.

ja1724

It's ok, but always best to run a PCV system. Unless its a drag car.

lars

Not if you want the best performance possible out of your engine. Even race cars use a positive crankcase evacuation system: Drag cars typically use a header collector extractor system, and road cars use engine driven vacuum pumps to evacuate the crankcase and keep a negative pressure below the pistons. By running just the breathers, you are allowing the crankcase to build up positive pressure which is detrimental to performance. It also allows the build-up of condensation in the crankcase and other corrosive gasses. There is no reason not to run a PCV system on a street car, and a lot of benefits from doing so.

agent kronus

does this still apply to a supercharged engine, with low compression?

Ive heard the pcv cant remove the gases quick enough, and lead to oil leaks etc.

Kid Vette

Are you sure he didn't have a breather in the air cleaner like in the pic?

mrvette

LARS, what is your comment on my using the airpump above which when the crankcase reaches an estimated 200f, runs only 2 lbs at idle, not the 5 on startup, and runs about 8-9 when 2500 or so is reached....

another additon to my list of comments is, that pump puts out some awful skankey smells.....got a whiff or 2 just now on a trip to HD and back....jeebus...drop a mountain Lion at 5 miles....