breather questions

ok.............. you have a lot of routes here.....................let me get this outta the way first....a breather is not emissions legal......with that being said it is up to you the route you go.............on a fox the pcv valve is supose to be on the back of the intake.............and a hose ran into you EGR and sent through the system to be "reburnt" again.............a breather vents the gases I.E. oil and gas vapor into the atmosphere.....hence it is illegal....but it does vent the crank case pressure FASTER. alot of people use them i am going to.....i have also been told by my freind building my motor with me that runing a tube from the valve covers into the header will work wonders. but i havnt decided yet for my combo.i dont know what you mean by oil leak but i do know a clogged or none working pcv valve will cause oil to be spit back up through the intake system and work its way into the air flow box.

p.s.if you have any more ?'s just holla.............

88stangmangt said:

.............and a hose ran into you EGR and sent through the system to be "reburnt" again.............

Click to expand...

PCV, as far as i know, has nothing to do with 'burnt' gasses - that is EGR.

i think some blower guys run with a check valve in something somewhere - Rick is really good about posting info on that stuff. (i cant remember if it is PCV related or vacuum related - brakes, etc).

if there is excessive crankcase pressure, it will try to find a way out (i.e. seals).

i haven't seen ya in awhile, Zeus. take care and good luck.

On the stock pcv system the pcv valve is nothing more than a check valve to keep air from flowing from the manifold to the crankcase. When the intake manifold is under vacuum (idle, throttle closed when slowing down, etc.), vacuum pulls on the crankcase 'ventilating' the crankcase blowby into the intake. That way any oil-laden/exhaust vapors aren't vented into the atmosphere. EPA regs mandated PCV systems years ago. Since the manifold is 'sucking' on the crankcase, air must be allowed to enter the crankcase so that vacuum doesn't build up there. That make-up air enters the crankase through the hose that runs from the throttle body to the nipple on the valve cover oil fill neck. Air from that source has already been metered by the maf; so all air entering the engine for combustion, even that which comes through the pcv valve has been metered.

Two things happen when you add boost. First, cylinder pressures increase which means that there's more crankcase blowby (some exhaust gets past the rings) and more crankcase pressure. So your pcv system has to be capable of venting that pressure into the manifold. However, the manifold is now under boost pressure - so the crankcase pressure may not be able to overcome the boost pressure. If it can't vent into the manifold, it will vent where it can. Without a valve cover breather of some sort - crankcase pressure will take the path of least resistance -- which is usually out the front and rear seals - taking oil with it. Perhaps that's why your rear main is leaking.

Second - the little hose connecting the throttle body to the valve cover will be under boost pressure. That's why those connecctions are usually capped off on a supercharged application - so you don't apply boost pressure to the crankcase. When that gets capped off - if there's no valve cover breather - air can't get into the engine when vacuum is pulling on the crankcase (non-boost situations). This often results in air being pulled in past the crank seals - some people actually hear 'whistling' as air gets sucked in past the thin seals.

For those reasons, breathers on valve covers often show up on supercharged cars - they let the crankcase vent when the engine's under boost; they let air into the crankcase when there's vacuum in the manifold - albeit unmetered air.

Make sense?

If you want an emissions-legal venting system, something has to be engineered that let's crankcase pressure be vented into the suction side of the supercharger -- and some type of trap/catch can is usually used so you don't have oily vapors entering the system there -- especially if the maf is on the downstream side of the charger where the oily vapors can foul the maf's hot wire sensor.

HISSIN50 said:

PCV, as far as i know, has nothing to do with 'burnt' gasses - that is EGR.

i think some blower guys run with a check valve in something somewhere - Rick is really good about posting info on that stuff. (i cant remember if it is PCV related or vacuum related - brakes, etc).

if there is excessive crankcase pressure, it will try to find a way out (i.e. seals).

i haven't seen ya in awhile, Zeus. take care and good luck.

Click to expand...

actually the gases from the crank case oil and gas fumes are sent back into the intake.......to be reburnt......that is the standard set-up for a "legal" Pcv system in cars today. the reason a breather isnt legal is because it is just vented into the air....and is as bad as exhaust emissions.

Can't help you with the breathers; I'd only plumb mine up so that those vapors were going back into the engine - others will be able to help you source that. Just know that most of them make a pretty good mess - you'll have an oily mist that will leave oil deposited all around the general vicinity of the breather. Go to your local Ford dealer - get a new pcv valve, grommet and screen for them for less than $20. All 3 pieces are important. The most overlooked is the grommet. The grommet hardens over time and fails to provide an air-tight seal for the pcv valve causing vacuum leaks.