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Specific answers:
There will be a slight vacuum in the intake manifold even at WOT. If there was no pressure differential there would be no flow.

Then I assume AEBS engine just has a standard open system venting excess blowby to atmosphere through the two valve cover openings. I assumed since the two openings are threaded that they hooked up to a catch can. If there is no manifold connection, the catch can would only would only be used to catch any excess oil and prevent it from getting on the track. The catch cans on most race cars are only that, catch cans. I don't know of many race systems that have a connection to the intake manifold, so the catch can can't function as a liquid/vapor separator as it does in a street application. A race system plumbed into the exhaust system might use a catch can as a separator.

only in a system that always maintains a crankcase vacuum would the crankcase filters always have air going through them one way. It depends on what type of system is being used. Since there are also different types of race systems,you will have to specify exactly what type of system you are referring to.
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But there IS a pressure differential...the intake valve has opened and closed rapidly. In a closed system you have resonating pressure cycles at the IM. I assume that the air has to go into the combustion chamber at a certain resonance frequency or else how else would it enter?

An opened intake valve with zero pressure across it's opening is going to have a hard time filling a cylinder at the brief interval provided at 8000 rpm or 10,000 rpm in a race motor.

So the PCV valve WILL experience a pressure differential between the crankcase and the IM at high loads. Your assumption of zero pressure differential across it does not make sense to me.


I agree that the function of a PCV is to prevent venting of crankcase vapors into the atmosphere and it is a controlled vacuum leak driven by IM vacuum.

Let's stick to the street car as a discussion focal point for now, so that we can at least pinpoint where we agree and where we differ and the assumptions we make.

If the purpose of the PCV system is to prevent atmospheric venting and the blow by gases exceed the venting crankcase gases, at high engine loads, why not close the system off from above and allow the extra blow-by gases to "push" the crankcase vapors out the PCV valve? The problem would be solved by having a sufficiently large enough orifice in the PCV valve? Why do you need to have a small PCV orifice that generates backing up, build up, and reverse venting out the valve cover? I don't see in any manual, this flow diagram of reverse venting.
 

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..adding another point of view that is intended to be to the point and clear...

The diagram should explain things clearly. You guys are overanalyzing WAY too much.

The breather hose makes fresh air come through the engine (not in the combustion chamber) to ventalate your crank and other engine internals. That's it. Looking at the diagram should explain everything. KISS.

one use of those little air filters are for turbocharged applications. When your force inducted air is coming up the pipe leading into the throttle body, it's quite hot and pressurized. You do not want that air to get shot through the crank. It'll heat up your oil temps and engine temps and on top of that you'll lose precious pressurized air from the turbo. Creating loss in power. By using one of those breather filters - you can retain a closed pipe for the forced inducted intake.

In a sense - it could help you retain horsepower for FI vehicles. The PCV system probably will not be as efficent with the filter since it's not receiving as much air flow from the IM vacuum. But it's not worth tapping into the intake for ventilation purposes IMHO..
 

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I am speaking only of the stock PCV system on my GSR.
Turbo systems are another story.

The main point I want to make is that at WOT the PCV valve connection at the intake manifold and the valve cover connection are at basically the same pressure because the throttle is wide open. The only reason they ever are at different pressures is due to the restriction caused by a closed throttle. only when the throttle is closed is there vacuum on one side. So at WOT, there is no reason for the vapor to prefer one opening over the other because they are at the same pressure. Do you agree?

Here's what I did:
I removed the hose at the valve cover opening and connected a vacuum/pressure gauge directly to it.
If the flow is always one way (into the intake manifold through PCV valve) there will always be a vacuum at this point. Agreed?

Here's what happened:
Most of the time the gauge would read around 5" vacuum. I did several pulls to redline through second and third, starting at slow speed in second. At the very end of the redline pull in second gear the reading would be about zero; it would stay there and only towards the the end of third gear would it start going slightly positive (.5 PSI). I would have liked to have done longer pulls, but I just went to a local back road; getting to the freeway takes a while.

What does this mean?:
The fact that there is positive pressure at the valve cover opening means that under extreme conditions the stock system on my car does indeed experience a flow reversal at the valve cover connection. The pressure at the valve cover opening would always have to be less than atmospheric for the flow to be only one way. The stock system does an excellent job. It maintained a vacuum in the crankcase under all but the most extreme conditions. Of course, if the valve cover opening was open instead of connected to the gauge, then the pressure probably wouldn't have gotten over atmospheric. I tested this way to demonstrate that there is a flow reversal. I would really like to do an extended high speed run - maybe later.
 

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pub on Aug/10/02 said:
..adding another point of view that is intended to be to the point and clear...

The diagram should explain things clearly. You guys are overanalyzing WAY too much.
pub dude who do you think put up the fricking diagram?
(in my Dr. Evil voice, pinky to edge of lip)

I don't think kelly and I have a hard time understanding the diagram. I can speak for myself anyway, because I was the one explaining to everyone else 3 years ago on Superhonda.com...all these newbie ricers would be slapping these $10 k&n breather filters on their valvecover and thinking they were hot sh*t...not knowing what they did or how the PCV system works IN A HoNDA.

Where kelly and I differ in opinion is not the way the diagram flows but whether the flow for the black arrows change when the engine load changes at WOT. he says that there's reverse crankcase flow (black arrows) up through the valvecover breather tube on top of the diagram from below in the crankcase because there is no vacuum in the IM at WOT. I disagree. I suggest that excessive flow goes through the PCV valve in one direction like the diagram and there is still fresh air flow down into the valve cover breather and then down to the crankcase even at WOT.

If someone can clear this up that would be appreciated.
 

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Haha, it's alright. You were the one steering in the right direction. I wasn't reading kelly's posts throughly because his ideas seemed far-fetched.

I still would have to agree with your opinion. I really think with the excessive intake flow the crank would also require excessive ventilation, thus increasing the effectiveness of the PCV as the throttle is increased. That's just my thoughts stepping back from the whole picture. The actual mechanics of the whole thing could prove to be different when actually put to the test. I however think Honda would have reconized this ordeal and made sure everything worked out just fine.
 

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well if kelly's scenario was correct, my oil catch can would be sucking backwards at WOT instead catching oil before it entered the PCV valve into the IM. The second problem he fails to see is that we are not dealing with a 457 chevy with a top mounted filter,TB, and carbs. The TB is upstream parallel to the IM. So when he says the vacuum pressure is zero with the TB plate opening, this would be true in a non- single plenum IM setup but in our Hondas there should be some pressure fluctuation in the IM pulling in fresh air from the intake and crankcase vapors from the PCV valve. The third thing he fails to recognize is that we are dealing with a resonance tuning single plenum IM...the intake pulse reverberates at a certain frequency. There has to be some vacuum in the IM even at WOT.
 

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I checked the PCV valve shortly before the test when I was studying the system. It's fine. I have experimentally verified that the theory is correct, so I'm satisfied. I had never tested a PCV system; I thought it would perform much worse than it did. Honda impresses again. Try some tests of your own and let me know what happens.
 

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I agree there is a slight vacuum in the intake manifold at WOT. I have repeatedely stated this. At WOT both the valve cover opening and the PCV valve connection at the intake manifold will be at EQUAL PRESSURES slightly below atmospheric. Since the crankcase pressure is now higher than the pressure at the other two openings due to the increased blowby, vapor will flow out of both of these openings. The real key is that both openings are at the same pressure at WOT. Just think about only this for a while.
 

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If you are using the PCV valve with this setup and it has the same size orifice as a stock one, then you should still get the same results as I did, because even though your system has two large connections from the block to the tank, when the tank is closed, all the flow still has to go through the tiny PCV orifice, which I assume is hooked up to the IM where the stock one was. The orifice is the limiting factor. If the orifice is bigger or if it doesn't have an orifice, then you might not get any positive pressure or any that's measurable with just a cheap vacuum/pressure gauge like I used. Yours might just go to atmospheric under load because your connection to the IM through the PCV valve flows more than stock and won't be as much of a restriction. But with your increased compression, you might have more blowby. Who knows? once again, the question is whether or not the connection at the valve cover and the connection at the IM are at the same pressure. If they are, then the flow will go out both places. Yours will have to maintain vacuum at the valve cover opening at all times in order for you to say the flow is one way. We won't be comparing apples to apples, but it will be interesting.
Read the catch can description at the Endyn site one more time, please.
 

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Now we are on the same page! If I do that, I will be measuring pressure differential between these two openings which has been what I have been stressing. But this setup won't allow me to tell which side has the higher pressure, and hence the direction of flow. All I will no for sure is that if I get atmospheric pressure at any time, that the pressure is equal at the two openings. That's why I tested the other way. The fact that I got a pressure reading at the valve cover meant that the PCV valve connection was not keeping up with the blowby and that there definitely would be a flow reversal.
Do you want me to tee into the PCV system at both the IM connection right next to the intake manifold and the valve cover breather hose connection right by the intake tube, or did you want me to disconnect the PCV system and connect to the intake manifold and the intake pipe connections directly? Either way, the above argument is still valid. Please explain the logic behind your request. I might be missing something.
 

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I don't understand; be more specific. The way I tested proved that on my car the flow of the PCV system reverses, if the PCV connection to the intake manifold always flowed enough to keep up, I would have never gotten any positive pressure at the valve cover opening. If I test the way you want me to, I won't be able to verify if the flow reverses, I will just get the average pressure between the two openings. For example, if I get a vacuum reading it could be because the PCV valve side has vacuum and the breather side is at atmospheric or the PCV valve side has vacuum and the breather side is above atmospheric or the breather side has vacuum and the PCV valve side has less vacuum. I can't prove direction of flow that way. All I will be able to prove is if the whole system can keep up with the blowby or not.
 

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kelly on Aug/11/02 said:
All I will be able to prove is if the whole system can keep up with the blowby or not.
exactly my point....

your hypothesis assumes the TB plate upstream from the PCV valve when it is open will be fed by fresh air and the vented crankcase gases. But you must replicate a closed system not an open one.

The whole point is that the open nipple supplies inadequate venting down into crankcase at WOT. What happens if the system is closed? In a catch can situation (SC/FI or N/A), the intake breather hose is still attached forming a closed system supplying adequate pressure down to the crankcase from the intake (as shown in the direction of the white arrows in the Honda diagram). By setting up the T-piece, you are merely doing what Honda intended and that is, to have the breather hose attached. Now take a vacuum reading at the breather hose. It should tell you if the venting is back to the intake or forward into the valvecover.
 
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