explain the pcv system to me

[IJ.]

Pete: Unless you have a 0 restriction filter element there's a vaccum

 

[Zumtizzle]

Here is how everything is hooked up now. the isc connects to the tb. i have no idle problems what so ever, car is on maft blow thru mode if that has anything to do with it. no boost leaks

What in the flying fuck.

Are you on drugs?

I've seen some shit that doesn't make sense. Then i saw this..................


Edit: If you're map based you can just have a little filter for the ISC valve.

 

[Facime]

Pete: Unless you have a 0 restriction filter element there's a vaccum

I thought JJ just explained that the vacuum in the accordian hose was next to non-existant? Are you now saying there is enough to provide postitive ventilation without the system plumbed into the TB post butterfly? 'Cause if you are NOW im cornfused lol.

How can so many not understand a simple orifice based PCV system? Heaven help them if they needed to fathom the valve type.

There is no vacuum in the accordion except under boost and even then it's not much. Why would there be? Just look at the induction system. The pressure drop across the air filter and through the AFM is tiny so why would there be a delta P between ambient and the PCV port? Isn't that the reason everyone likes those "free flowing" air filters? Because they want as low a drop as possible? Put a plastic bag over the air filer and sure, you'll get low pressure on the port, but with a clean air filter there's none there. Less than a tenth inch h20. For those who don't buy into this measure it and see

 

[IJ.]

It's still there though and as the crankcase is + pressure it doesn't take much to move the gasses in the right direction. >>>>

This is how mine is plumbed but it requires large bore fittings and hoses to function (-10)

 

[jetjock]

We're talking about tenths of an inch/h20 at rpms where the engine spends most of it's time. It's from 1) the slight pressure drop across the air filter and AFM and 2) flow across the port at right angles. Think blowing across the top of a bottle. IJ is technically right though. And larger plumbing does help but it's still not the way I'd want it...

 

[IJ.]

JJ: What size is the orifice in the stock system?

 

[jetjock]

Offhand it escapes me. Around .187-.200 iirc. Maybe .250

It's less than the port though. Must be why they call it an orifice eh?

 

[Facime]

I see, so it only needs to be positive by any degree to work, and the gases are not in actuality being "vacuumed" out? I happily admit that my understanding of the PCV system, especially when it comes to turbo applications, was deficient. :nono: (never too old to learn.)

 

[IJ.]

Offhand it escapes me. Around .187-.200 iirc. Maybe .250

It's less than the port though. Must be why they call it an orifice eh?

LOL here bastard
(lucky for me I was between mouthfulls of coffee)

I see, so it only needs to be positive by any degree to work, and the gases are not in actuality being "vacuumed" out? I happily admit that my understanding of the PCV system, especially when it comes to turbo applications, was deficient. :nono: (never too old to learn.)

Yep just needs a nudge in the right direction, it WON'T work with the standard size ports and fitting on the Cam Covers though.

 

[jetjock]

Understanding of the PCV system can be gained by visualizing the pressure differences at each end of the piping under both conditions and the resulting flow cause by those differences.

When the manifold is less than ATM flow is into the throttle body port with the accordion providing dilution (fresh) air. When the manifold is above ATM (boost) flow is towards the accordion with the manifold providing dilution, although not as clean. The right angles of the stock valve cover ports to the TB line provide a little help in scavenging and in both conditions crankcase pressure aids flow. The system is a compromise but it works.

Increasing the plumbing volume increases the conductance of the system so that a greater volume of gas can be moved with less of a delta P.

 

[IJ.]

aka: The Big Pipes does work hyuckk hyucckkk

 

[jetjock]

Lol, they do. I made all that up btw...just like the first post