Re-metered air and the valve cover breather

[FordFociSHO]

I don't have the stock setup in place but for those that do, this is for you.

What is the sense of metering air and them metering it again? Normally that would create a slight lean condition. Being the volume of air in the crank case is pretty much a fixed volume and any blow by gasses would already have gone through the mass air meter and been accounted for, why then would Ford put the breather before the mass air meter?
Doesn't make too much sense does it.
Granted there is not a huge flow of air coming through there, but there still is flow.

The flow of air through the intake tube can create a greater pressure differential than in the air box, in turn making the valve cover breather work better (properly). But you can not use a simple nipple to the tube, flush'ish with the inside wall of the tube. A design like a syringe needle is optimal, angled cut and opening. Think of it like sticking your hand out the window at 60mph, palm flat to the oncoming air. Your palm is the high pressure side and the back of you hand there is a low pressure area. This effectively creates a vacuum because the faster moving air will pull the slower moving air.

IIRC the AEM tubes and some of the ebay ones have a nipple for the VC breather. If someone could verify that they are just a flush cut nipple would be great.


The other reason I bring this up is because the fact that most of us always have oil in our intake manifolds. Vacuum can not move a fluid. It's impossible. Pressure is what moves oil up the tubes and into the intake.



This will probably just be considered one of my many rants about how piss poor these cars are though out and engineered, but there it is. Food for though.

[RallyRacer]

Remove PCV valve, install a hose barb routed to a catch can on the firewall. Block te PCV manifold inlet with a large vacuum cap. Works great for me, and no oil in my manifold.

[G-forces]

Originally Posted by FordFociSHO

A design like a syringe needle is optimal, angled cut and opening. Think of it like sticking your hand out the window at 60mph, palm flat to the oncoming air. Your palm is the high pressure side and the back of you hand there is a low pressure area. This effectively creates a vacuum because the faster moving air will pull the slower moving air.

There is a hack like this for Honda's I've seen (I posted it up once). It apparently works well for lowering pressure in the crackcase. I think it would work really well if you pared that up with the check-valve thingies you posted about last year. That way you should always get a vacuum in your crackcase at any throttle opening (N/A, of course, and stock, non-SVT, manifold), especially if you did both things.

[myfafp3]

a friend of mine gave me an "AEM" ram air ( i know it isnt cuz there isnt a carb sticker and the logo is a random sticker he put on it. it is for the focus cuz the rubber neck that connect to the throttle body is angled the same as the factory plastic intake.) and it doesnt have the nipple for the tube your talking about. what air is flowing thru there? i was just thinking about it cuz now there is a smell in my car when im stopped. i put my finger on the valvecover port and it started sucking my finger pretty hard then i heard a squeeling noise so i took it off. is it supposed to be pulling vacuum or blowing air out(thats what its doing now)?

[G-forces]

Originally Posted by myfafp3

a friend of mine gave me an "AEM" ram air ( i know it isnt cuz there isnt a carb sticker and the logo is a random sticker he put on it. it is for the focus cuz the rubber neck that connect to the throttle body is angled the same as the factory plastic intake.) and it doesnt have the nipple for the tube your talking about. what air is flowing thru there? i was just thinking about it cuz now there is a smell in my car when im stopped. i put my finger on the valvecover port and it started sucking my finger pretty hard then i heard a squeeling noise so i took it off. is it supposed to be pulling vacuum or blowing air out(thats what its doing now)?

For N/A motors :
At idle the crankcase vent will be sucking air in if you leave it open to the air. The PCV line goes into the intake plenum under the TB, so when the engine is running and the TB is closed (only the small IAC port is open) there is allot of vacuum in the plenum and the crackcase. So, any opening down-line from the TB will suck air at idle. When the tube is attached to the airbox there is a tug-of-war between the intake tube and the crank vent tube so a little vacuum (less than if it was blocked off) is felt inside the crackcase AT IDLE.

When you run with an open TB (especially at WOT) the vacuum inside the plenum is less, or equal to ambient air pressure, and the PCV stops doing much. The crankcase air (blow-by) is scavenged by the vent tube into the intake tube (or airbox if stock). You should feel a little pressure from it while running and a little vacuum from it at idle.

[chewbacca]

it doesn't matter that the air coming from the valve cover vent is already metered because it has already been burnt before entering the crank case then the head, so it really doesn't count as reburnable air, most likely it is just excess emissions like CO2 and CO and other bad gasses.

[FordFociSHO]

Start your own damn thread.

[G-forces]

Originally Posted by FordFociSHO

The other reason I bring this up is because the fact that most of us always have oil in our intake manifolds. Vacuum can not move a fluid. It's impossible. Pressure is what moves oil up the tubes and into the intake.

I just reread this and started thinking (ouch), vacuum does move things, because it creates a pressure difference. Compresed air moves things in it's path when released because there is a difference in pressure between the air in the tank and the outside air, so air rushes from high to low pressure, moving things in the path of flow. When you create a vacuum there is a difference in pressure between the vacuum chamber and the outside air (so that the outside air is like the pressurized air in a tank relative to the vacuum), when you let air into the vacuum area it rushes in and moves things as well.

Technically, it is the pressure difference that moves the air and the moving air carries whatever liquid or aerosol-ed oil with it, until the air slows down, cools, and drops the liquid (oil). While your right, it's not the vacuum that directly moved the oil, never-the-less, it is the creation of the vacuum that set the conditions for the pressure difference that allowed the higher pressure air to move the oil. So, a short-cut way of thinking about it is that the vacuum "draws" the oil into the manifold, even if that's not an accurate description of how it happens.

[myfafp3]

ok this makes sense now it didnt affect my idle or anything. no change in performance at all. thanks for the info