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Discussion Starter #1
Does any one know what the purpose of the valve cover breather really is? some people have the hose that goes from the valve cover to the intake, and other s have the breather on the valve cover and they seal off the hose on the intake. Whats the difference.?
 

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Its not about getting air faster out the valve cover.
Not everything that has a hose on it means if you put a air filter on it it will make your car faster. The Air Valve cover filter is one of them. The air needs to recycle itself. Air breathers dont get to recycle vapours that the engine needs to get back. Just dont get an Air breather, if your thinking about getting one really do your homework about it carefully because theres more to it then you may think. Key thing to remember dont follow the crowd, 98% of then where not informed like you. Just because it looks good dont mean it operates good.
 

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The breather helps ventilate the crankcase. It surprises me how many people mistakenly think the air blows out into the intake so they think removing it will give them more power. Talk about misinformed. Mike D posted a good write up on this before:


Here's the stock PCV diagram from the Helms manual. on the left is a cutaway view of the engine. on the right is a cutaway view of the stock intake. In the middle are the separate breather circuit and the PCV valve circuit:



all you have to learn is how the fresh air cicuit flows (follow the open white arrow) and how the crankcase vapor (with oil vapors in it ) circuit flows (follow the black arrows). Notice which circuit flows to the valve cover (on top of the engine on the left)....it's NOT the crankcase vapors. When you add a breather, you remove the line from the intake to the valve cover.


The honda crankcase breather is a POSITIVE pressure ventilation system.The air from the intake blows into the valve cover. It is NOT a negative pressure ventilation system...it does NOT suck air from the valvecover to the intake.

Breathers remove the source of positive ventilation that repressurizes the POSTIVE CRANKCASE VENTILATIoN (PCV) valve.

There is less pressure in the crank when you add a breather at the valve cover. The consequence of this is you get more positive blow-by from the combustion chamber past the piston rings and into the crankcase. More blow-by means less cylinder pressure...less cylinder pressure means the burn is slower and less complete...the result is more emissions and less power.

If you want to do this right and remove oil vapor from the circulating crankcase before it goes into the intake valve then, get an oilcatch can and put a breather on the catch can. Then place the catch can in between the valve cover breather and the PCV valve.

Disconnecting the breather tube, which blows fresh intake air into the valve cover, and placing a breather on the valve cover just creates more blow-by and emissions. Eventually you have so much blow-by, you lose power.
 

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With a breather in place you are going to lose PCV (Positive crankcase ventilation). There used to be a great thread explaining why this is bad, but it's gone now. I did manage to find a decent explanation on the site:
http://www.hastingsfilter.com/engineering/tsb_94-2r.html

Here is a portion of what it had to say.

"A neglected PCV system will soon fail to function and the result can be expensive as well as troublesome for the car owner. If the crankcase is not adequately ventilated, the motor oil will quickly become contaminated and heavy sludge accumulations will begin to form. Internal parts, not protected by the motor oil, will begin to rust and/or corrode due to the water and acids that will become trapped within the crankcase. If the PCV system is not functioning properly, the flow of crankcase vapor into the intake manifold will not be properly metered. This, in turn, will upset the fuel/air mixture for combustion and cause rough idling or even stalling of the engine. Furthermore, intake and exhaust valves, in addition to spark plugs, may well be burned and rendered useless, prematurely affecting performance and requiring expensive repairs. To assure trouble-free performance of the PCV system and, in turn, the engine and vehicle, routine maintenance of the PCV system is absolutely recommended and required."

Hope that helps you out.

EDIT: Geez I'm slow.
Anyhow that was the post I was thinking of.
 

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i have a slight kink in the rubber tube from the valve cover to the intake tube, is it okay?
 

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Discussion Starter #6
So why do they even sell that piece of crap breather, Im about to go home and launch that breather into the hudson river!! I'll stick to the hose from now on.
 

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I honestly don't know what the whole reason behind the breather filters are. Without the intake helping to create the possitive pressure the engine won't suck in any fresh air and the crankcase will not be ventilated correctly. But seeing them at an autoparts store in a little bucket labeled $3.99 was a good sign to me that they were useless.

I think Endyn's breather kit (with oil catch can) has some sort of configuration for turbo setups, I'm not sure.
 

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Under low load/low speed situations when there is little blowby and high manifold vacuum, fresh air will be drawn through the opening in the valve cover, down to the crankcase, through the PCV valve and into the intake manifold. Under high load/high speed situations when there is high blowby and very little manifold vacuum the pressure in the crankcase due to the increased blowby will result in crankase vapor flowing into the intake manifold AND out of the opening in the valve cover. The PCV system can only "pull air" at low speeds/loads. At higher speeds/loads both openings turn into vents because the crankcase pressure due to blowby flow has become so much greater. Whether the valve cover opening is connected back to the intake tube or has a filter doesn't really make much difference. Although from a flow standpoint, it is slightly better to have the valve cover opening connected to the intake because even at full throttle the pressure in the intake will be slightly below atmospheric. The reason newer cars have the valve cover opening routed back to the intake is so that the vapor that escapes through this route under high crankcase pressures does not escape directly to the atmosphere, it too is burned. More here. Stock PCV systems are designed more to reduce emissions than for horsepower. Check out drag cars, many have the crankcase vapors routed to check valves in the exhaust pipes. This system actually pulls crankcase vapors from the crankcase at high load/high speed by using the low pressure generated due to the exhaust flow. The vapors are not recycled and burned. This is the way it should be for increased horsepower. This system doesn't pull air at low speeds because the exhaust gas velocity isn't high enough to pull a vacuum, hence check valves. NASCAR engines use their dry sump oil systems to pull a vacuum in the crankcase. Two problems: oil separation and insufficient venting.here
 

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I used the slash-cut tube method MD posted. I went and check the factory pipe and breather tube and realize that the breather tube actually sticks out inside the pipe. Meaning it does not flush with the inside wall of the pipe.

I hope that made sense.
 

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you have to remember that oil vapor into the IM cannot be helping your cause. The oil vapor occupies space or volume. That means less air/fuel mix going in wuth one gulp of the intake valve opening.

The thought behind the breather is that you are supposed to get more fresh air flow down into the crankcase from the valve cover. This increases the cycle of oil vapor flow out of the crankcase. The added fresh air displaces the oil vapors in the crankcase with the assistance from the IM vacuum sucking it out. You evacuate the crankcase more effectively...or so the thought behind it goes. Remember you have converted a closed system into an opeb PCV system when you add one of those breathers.

We have a PCV system designed as a closed system though. When attached to the intake, the breather hose actually generates more pressure gradient to push fresh air down into the crankcase via the valve cover breather from the intake at higher engine speeds! When you use only 1 breather in an open system, not enough fresh air coming through the breather filter gets down to the crankcase.

The crankcase has less pressure inside. This opens the door for more blow-by. Without the positive pressure in the crankcase to offer some resistance to blow-by past the piston ring, you get crap going down. The other problem with less fresh air entering is, as was said before, the circulation flow out to the PCV valve is decreased. So more crap stays in the crankcase. It becomes a vicious cycle.

If you insist on using an open PCV system then drill a second hole and mount a second breather tube in the valvecover. Using 2 breather filters will deliver enough fresh air down to the crankcase. This is what the AEBS boys did with their race B18C1 that ran in the 10's all motor:





Now the other smart move would be to use an oil catch can that is baffled so that it captures or intercepts the oil in the vapor leaving the crankcase before it reached the PCV valve and enters the IM. Now you have more fresh air entering the IM instead of oil vapor.

If you plan to use an open system, add more breathers. If you use a closed system or an open system, use an oil catch can.

The good oil catch cans have baffles and drain the captured oil back to the oil pan without you having to empty them periodically.

cheers
 

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I disagree with your statement that the breather attached to the intake generates positive pressure to force air into the intake. I have other disagreements but will stay on this one for now. The pressure inside the intake tube will always be less than atmospheric with the car running. If it wasn't there would be no airflow.
If you look at the way the factory tube is slash cut you will see the slash is on the downstream side creating a low pressure area due to the increased air velocity. I just looked at my stock tube and it has no slash cut - my CRX did. So the slash cut is irrelevant, and it would be the only possible way to get any positive pressure there. The intake velocity would have to be impossibly high to make any difference. I'm going to have to hit the books - haven't studied fluid dynamics in quite a while.
 

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I have no problem with peole disagreeing with me. But you should look at that diagram from the Helms manual I posted up 3 years ago on SHO's tech archive which SurferX has kindly put up.

the flow of air is not into the intake from valve cover via the breather hose. The flow is from the intake TO the valve cover. (refer to the white arrows strating on the far right as it enters the intake)

yes the air is being drawn into the intake (less pressure) and down to the valve cover.

please refer to the Honda PCV flow diagram.

The other point is you don't want the reverse direction of flow. If you breather filter is getting oil on it, something is drastically wrong (if you look at Honda's flow diagram for the PCV). In addition, those filters don't work very well if oil is on them?

This has nothing to do with fluid dynamics. But I look forward to your input.
 

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That diagram is indeed correct for low load/low speed operation. At high load/high speed both sides of the PCV system are at slightly less than atmospheric pressure. There is no pressure differential between them unlike at low load/low speed when the intake manifold where the PCV connects has high vacuum and the connection for the valve cover has slightly less than atmospheric. When the throttle valve is wide open there is no pressure differential between the two openings because the throttle plate was the separation between the two openings. So there is no reason for air to flow either way because there is no pressure differential. When at high load/high speed there is a lot of blowby volume which will go out both openings because they are at the same pressure. Check out the links I posted again; both verify that at high load/high speed things change.
 

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here's a clearer view of the honda pcv diagram:




here is the pic of the pcv valve at different engine loads:



the flow is in the same direction at higher loads, it's just that the valve opens more to allow more flow from the crankcase. the direction of flow and flow paths do NOT change. In fact if your explanantion were true then there would be no reason for AEBS to drill the second valve breather tube when they "opened" the PCV system.
 

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I agree, the connection to the intake manifold will always flow that way. The flow in the valve cover connection is what reverses. I imagine the AEBS engine has only those two vents. There is no need to hook up anything to the intake manifold since under drag race conditions there is almost no vacuum present. Also, as we agree, running any oil vapor back into the intake manifold hurts power. The vents are either just hooked only to a catch can or to the collector. Are they running a dry sump? If they are, these are just 2 intakes as the pumps are pulling the blowby out. If I go back to look at picture I will lose all I have written. Imagine a #3" PVC pipe with a butterfly valve in the middle. on one side of the valve is the PCV hose connection on the other side is the valve cover connection. The two hoses are teed together with another hose. This other hose that is teed in represents the crankcase.If you were to suck on the side where the PCV valve is connected with the valve closed, air would flow through both of the other hoses. This would be low load condition. If you now open the valve and suck, most of the air will just come from the other end of the PVC tube. A little air would come through both the PCV connection and the intake manifold connection thru the crankcase connection at the T. Now do the same (valve open senario) but with someone blowing in the crankcase hose. Now air is being pulled ever so slighly thru both hoses thru the crankcase tee, in addition to being blown out by the other person. This is high load condition. Did you read my links? once the blowby flow into the crankcase becomes more than flow out of the crankcase due to intake manifold vacuum the crankcase becomes pressurized and vapor will flow out of both vents. This will always happen with this type of system because at WOT the pressure at both the manifold and the PCV conection becomes equalized at close to atmospheric but the crankcase pressure rises due to the increased blowby. If the connection to the PCV valve is much larger than the connection at the valve cover, then most of the flow would be through the PCV connection, but a little would also blow out of the intake manifold connection. If both connections are big enough then there really would never be any flow at all because there would never be a pressure difference. I'm taking a break. Look forward to continuing discussion later.
 

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kelly on Aug/09/02 said:
I imagine the AEBS engine has only those two vents. There is no need to hook up anything to the intake manifold since under drag race conditions there is almost no vacuum present.


The IM on the AEBS is a little trick one with twin humungus BK TB's hooked up to a trick plenum with very short straight runners with velocity stacks and no there is no breather hose venting connection to the IM.

I haven't datalogged a race only drag engine but I find it very difficult to believe that there is no vacuum at the IM.


The vents are either just hooked only to a catch can or to the collector.

No the vents are open.


Are they running a dry sump? If they are, these are just 2 intakes as the pumps are pulling the blowby out.

No they are using a standard wet sump system.

Imagine a #3" PVC pipe with a butterfly valve in the middle. on one side of the valve is the PCV hose connection on the other side is the valve cover connection. The two hoses are teed together with another hose. This other hose that is teed in represents the crankcase.If you were to suck on the side where the PCV valve is connected with the valve closed, air would flow through both of the other hoses. This would be low load condition. If you now open the valve and suck, most of the air will just come from the other end of the PVC tube. A little air would come through both the PCV connection and the intake manifold connection thru the crankcase connection at the T. Now do the same (valve open senario) but with someone blowing in the crankcase hose. Now air is being pulled ever so slighly thru both hoses thru the crankcase tee, in addition to being blown out by the other person. This is high load condition.

This is not the scenario in a Honda. In a Toyota or Mitsubishi or Ford perhaps but not in the Honda PCV system. The flow is in one direction regardless of loading...a unidirectional loop.


once the blowby flow into the crankcase becomes more than flow out of the crankcase due to intake manifold vacuum the crankcase becomes pressurized and vapor will flow out of both vents. This will always happen with this type of system because at WOT the pressure at both the manifold and the PCV conection becomes equalized at close to atmospheric but the crankcase pressure rises due to the increased blowby. If the connection to the PCV valve is much larger than the connection at the valve cover, then most of the flow would be through the PCV connection, but a little would also blow out of the intake manifold connection. If both connections are big enough then there really would never be any flow at all because there would never be a pressure difference.

If there was excess blow-by exiting via reverse flow up away from the PCV valve and up to the valve cover from underneath and the oil vapors vent out the valve cover breather tube, you would have no pressure venting the crankcase vapor to the PCV valve and then to the IM.

Secondly, this is not what those little valve cover breather filters were meant for. They filter the incoming air. They do not filter outgoing, oil saturated crankcase vapors or excessive blow-by. Why would they? you're not trying to pass emissions in a race engine. They do not handle oil vapors very well. You saturate them with oil and they do not filter. Hence, under your scenario at low loads, when the flow supposedly returns back to the intended direction down to the crankcase, you would have crap going down to the crankcase as well, sludging up the oil. It just doesn't wash.

Sorry but your reverse flow under high load hypothesis and T tube analogy is not the setup here. It is a unidirectional loop and a more appropriate analogy would be a staight tube with a spring loaded valve in the middle dependent on the degrre of suck. on one end is the IM on the other is the crankase. In series before the crankcase is a pump with a side siphen to this tube. The degree of siphening off the pump (intake fresh air) is dependent upon how much the valve opens at the opposite end downstream.

A failed "siphening" from the pump has more negative pressure in the crankcase allowing more and more blow-by.

The system can fail from inadequate fresh air flowing down to the crankcase or inadequate PCV valve opening for the given engine load.

cheers
 

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why do you think race engines run vacuums in the crankcase? it's not to vent gases back up and out thru the top at the valvecover....that's for sure. It's to pull more fresh air down to the crankcase which then leaves either through the vacuum or through the PCV valve. You can just as easily vent crankcase gases out the PCV valve into the atmosphere rather than back into the IM. You don't need it to spew backwards up to the valvecover and then out the valvecover breather tube as you describe in your scenario ....

cheers
 

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A race system and a street system are optimized for different purposes. A street system is optimized to reduce emissions at normal street loads, while a race system is designed to increase power under all, or at least, race conditions. A street system can never be allowed to vent the oil vapors to the atmosphere, that is the only reason it is a closed system. Being forced to be a closed system is what really limits it's effectiveness. It fails to maintain a crankcase vacuum under high blowby conditions.

The following applies to the stock Honda closed PCV system:
The Honda PCV system is a metered vacuum leak. It can only flow a limited volume of air, and it's highest flow potential is when the intake manifold vacuum is highest. Under normal street conditions there is a small volume of blowby and the intake manifold vacuum is high. The volume of air coming in through the valve cover opening and going out through the PCV to the intake valve is sufficient to keep up with volume of blowby. The crankcase is kept under a slight vacuum. If you look at the stock PCV valve you will see that it is not a variable orifice valve; it is a check valve with a fixed orifice. This design means that the PCV system's flow rate is governed strictly by the difference in pressure across the valve.
Under heavy load/high RPM conditions the PCV system has it's lowest flow potential because the intake manifold vacuum is very low and equivalent to the pressure at the valve cover inlet because the throttle is wide open and both sides of the system are connected. There is no pressure difference across the system and hence no flow. At the same time that the PCV system flow has stopped the blowby volume has increased. So now the blowby flow volume exceeds the PCV flow volume (which is zero). The crankcase becomes pressurized and the pressure escapes through the two routes it has available (through the PCV valve into intake the manifold and through the valve cover opening). More vapor will flow out of the valve cover opening because the PCV valve has the fixed orifice in it which is much smaller than the diameter of the hose. The question now is if the drawback to having most of the blowby sucked back in by the engine causes more power loss than does the elevated crankcase pressure. If the system were open, we wouldn't have this dilemma.
The ideal conditions are a slight vacuum in the crankcase at all times with no blowby vapors returned to the engine. A good system will accomplish this. Many race systems don't even do this; they merely keep the crankcase pressure no higher than atmospheric. An over scavenged dry sump system is probably the only system that maintains constant crankcase vacuum. Most other systems either maintain a vacuum only under high load (collector system) or just keep the crankcase pressure at atmospheric (standard open system). Since the street system has to be closed, it is a major compromise as far as power is concerned.
Hook up a vacuum/pressure gauge to the stock PCV system valve cover connection and see what happens. I haven't done this myself - am going to.
 
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