valve covers w/ breathers or w/o

v850mustangluvr · Nov 9, 2004

i found a pair of valve covers on ebay that have holes w/ breathers put in them.....what is the advantage or disadvantage to having breathers??

thanks for any help coming my way!!

Stang8URMPRT · Nov 9, 2004

I have read that if you use Carb Valve covers (with breathers) on an EFI, it can cause vacuum leaks. Don't ask me how this happens or why, but almost all adds (from good sellers, aka Jegs, Summit) will state this.

HISSIN50 · Nov 10, 2004

if one uses breathers on an EFI MAF car, there will be unmetered air entering the engine.

PhLoBuS · Nov 10, 2004

I have one and I have no problem at all, you are talking about the oil cap right?

Allforspeed · Nov 10, 2004

as long as the hole where the oil breather usually goes into you should be fine.........right guys??

HISSIN50 · Nov 10, 2004

Allforspeed said:
as long as the hole where the oil breather usually goes into you should be fine.........right guys??

stock EFI stangs dont have any breathers. the PCV re-routes air so as to keep the system 'closed'. an open breather allows unmetered air.
but im not sure im following you guys.

v850mustangluvr · Nov 10, 2004

what size breather fits the oil cap?

HISSIN50 · Nov 10, 2004

v850mustangluvr said:
what size breather fits the oil cap?

they sell ones that screw right into where the oil cap goes.

Boss 351 · Nov 10, 2004

Isn't the closed system for anti-pollution? I got a carb'd 302 right now with two breathers, the thing will have a constant oil mist coming out. In fact the mist pops out of my hood scoop at red lights... I've even tried some more expensive K&N oil breathers and it still mists oil lol.

TT91 · Nov 10, 2004

HISSIN50 said:
if one uses breathers on an EFI MAF car, there will be unmetered air entering the engine.

I sure hope your being sarcastic......

GroverDill · Nov 10, 2004

I agree with Hissin50

Boss 351 · Nov 10, 2004

Positive Crankcase Ventilation, has nothing to do with the MAF...

Anyway check this out: http://www.mustangworks.com/articles/powertrain/StandTall.html

And this: http://www.lapelec.co.uk/PCV.htm

TT91 · Nov 10, 2004

Groverdill, long time no see, please explain why you agree with him.

krahkin · Nov 10, 2004

What do valve covers have to do with air intake? If by some chance air was sucked in to your valve cover through a breather, it would not affect your engine performance. There is no air inlet in your valvetrain that mixes with gasoline and combusts. If there is, it's news to me

crazypete · Nov 10, 2004

Do the PCV gasses affect the mixture at all? Is there enough there to make any difference?

With breathers on my valve covers, they basically steam. Is this combustion gasses or oil vapor?

MustangMuscle86 · Nov 10, 2004

crazypete said:
Do the PCV gasses affect the mixture at all? Is there enough there to make any difference?

With breathers on my valve covers, they basically steam. Is this combustion gasses or oil vapor?

It's more than likley oil vapor...about the only way it's combustion gases is a cracked head or a broken head gasket somewhere odd.

Boss 351 · Nov 10, 2004

crazypete said:
Do the PCV gasses affect the mixture at all? Is there enough there to make any difference?

With breathers on my valve covers, they basically steam. Is this combustion gasses or oil vapor?

oil vapor... You'll also need to clean your valve covers more often - at least that's the case with me. The PVC gasses are sent into your carb/EFI intake to be burned up instead of being set free into the atmosphere.

GroverDill · Nov 10, 2004

Under vacuum conditions, engine vacuum sucks on the crankcase through the pcv valve. It pulls any blowby into the intake manifold. Because you don't want to create a vacuum in the crankcase, there has to be a path to LET METERED AIR INTO the crankcase. That's what the little hose between the throttle body and the valve cover nipple are for. Under high manifold vacuum, metered air travels from the throttle body to the crankcase through the valve cover nipple. Some people who remove the hose and cap off those openings hear squealing sounds under vacuum as air gets pulled into the crankcase past the front or rear seals.

At w.o.t., there is crankcase pressure, and atmospheric pressure in the intake manifold - no vacuum. If the crankcase pressure is greater than the manifold pressure then crankcase venting will occur through the pcv valve/line AND through the valve cover to throttle body line. You can now see that the throttle body to valve cover line is bi-directional. Under some circumstances, air moves from the t/b to the crankcase; under other circumstances air moves from the crankcase through the throttle body. At part load when there is low manifold pressure and low blowby (crankcase pressure) the differential can't overcome the small check valve in the pcv, so venting of the crankcase occurs through the valve cover to throttle body line.

That's what that hose is for. There is absolutely no performance benefit to disconnecting/capping it off - and it may be detrimental. If you have a functioning pcv hooked to manifold vacuum, I'd hook it back up. For breathered valve covers, it's unnecessary.

this is a copy of a post from or own Mr Yount.

crazypete · Nov 10, 2004

So this will probably clog/oil up my carb after a while, wont it? I should inject this under the carb rather than above.

90NotchBack · Nov 10, 2004

Boss 351 said:
Isn't the closed system for anti-pollution? I got a carb'd 302 right now with two breathers, the thing will have a constant oil mist coming out. In fact the mist pops out of my hood scoop at red lights... I've even tried some more expensive K&N oil breathers and it still mists oil lol.

That is called blow by! On most racecar they have vacuum pump to suck out all the moister in the motor Or they run some hose to the header and let the exhuast suck it out. Like this

valve covers w/ breathers or w/o

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