I've been reading up on the way that the factory intake is designed to have a slash cut tube connecting the breather on the valve cover to the intake arm...from what i understand, this is to draw air INTO the crankcase and force the blow off gases to exit through the PCV system.

well upon inspecting my aftermarket intake, i noticed that there is no slash cut...but rather just a flush fitting and low and behold...a trail of oil leading to the throttle body. so obviously oil/vapors are being sucked into the intake manifold because the crank case is being put under vacuum. now i can imagine that this would contribute to oil consumption and poor combustion.

i'm just wondering why aftermarket manufacturers dont take this into account when they design their intakes. it seems like a pretty critical component in making sure the PCV system is working properly...


the slash should be like this....

_________________________

air =======>========> throttle body
___________/|____________

Modified by JOHN WAYNE at 2:23 PM 7/25/2005


Modified by JOHN WAYNE at 2:00 PM 7/27/2005


Modified by JOHN WAYNE at 2:03 PM 7/27/2005

 

no thoughts on this?

 

i believe its to pull excess vapors, thats why turbo setups and such put the slash cut tube in the ehxust from the valve cover. to increase the pulling effect not pushing.
sean

 

after looking over the PCV diagram in the helms it is definitely clear that the air is supposed to move from the intake arm INTO the cylinder head through the breather passage. this forces the crankcase vapors out through the black box on the rear of the block...

this is achieved through the slash cut design of the intake arm. there is just a SLIGHT tip that you can feel on the inside of a stock GSR/ITR intake arm where the breather enters the arm. without the slash cut you do not get this desired effect and you will be working against the PCV system.

 

the pcv valve has vacuum from the intake manifold sucking it open, so if you're saying that you'd rather see your crank case having air forced into it rather than 2 places where pressure can exit, be my guest.

 

ok clearly the fresh air flow comes from the intake INTO the head...then helps PUSH (positive pressure) the vapors out of the block...

the only way to make this happen is to have a slash cut with the slash facing the flow of incoming air...as air gets sucked into the intake manifold, some of it will get routed into the head.

case closed.




Modified by JOHN WAYNE at 10:09 AM 7/27/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 91civicDXdude &raquo;</TD></TR><TR><TD CLASS="quote">the pcv valve has vacuum from the intake manifold sucking it open, so if you're saying that you'd rather see your crank case having air forced into it rather than 2 places where pressure can exit, be my guest.</TD></TR></TABLE>

i'm not talking about the valve...the valve is what allows the vapors that have been pushed out of the crankcase to be recycled through the intake manifold...i'm talking about the breather passage that runs to the intake ARM.

 

You've got it backwards.

Its supposed to draw air OUT of the block and INTO the intake to be burned and exhausted. As far as the oil, that is normal.. You can invest in a catch can for the oil. Greddy makes a good one, although expensive. I personally believe that it is unnecessary, or the car would come with one.

As far as the slash cut tube, I'm sure it aids suction. But it also gets into your air flow and causes turbulence. As long as the fumes are being vented from the block, I see no problem.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by phyregod &raquo;</TD></TR><TR><TD CLASS="quote">You've got it backwards.

Its supposed to draw air OUT of the block and INTO the intake to be burned and exhausted. As far as the oil, that is normal.. You can invest in a catch can for the oil. Greddy makes a good one, although expensive. I personally believe that it is unnecessary, or the car would come with one.

As far as the slash cut tube, I'm sure it aids suction. But it also gets into your air flow and causes turbulence. As long as the fumes are being vented from the block, I see no problem.


</TD></TR></TABLE>

no...i dont have it backwards...cant you understand the diagram above??

<FONT COLOR="blue">FRESH AIR</FONT> comes into the ENGINE HEAD from the INTAKE ARM...not the intake manifold

this <FONT COLOR="blue">incoming air</FONT> puts pressure (this is why its called positive crankcase ventilation) on the crankcase and the <FONT COLOR="red">BLOW BY VAPORS</FONT> exit through the back of the block into the INTAKE MANIFOLD and are combusted and yadda yadda....

without a SLASH CUT design, the vacuum from the intake manifold will pull vapors and oil OUT OF THE HEAD...working against the design of the system.

why is this so hard to understand??

 

JOHN WAYNE your right about the design standpoint your discussing.

So you would invert the slash cut so the angle would be pointing towards the incomming air? if so i dont think it would work.
not only aftermarket intakes, but stock intake arms dont have slash cuts either, because as you say you want positive pressure on the valve cover went , not negative.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller &raquo;</TD></TR><TR><TD CLASS="quote">JOHN WAYNE your right about the design standpoint your discussing.

So you would invert the slash cut so the angle would be pointing towards the incomming air? if so i dont think it would work.
not only aftermarket intakes, but stock intake arms dont have slash cuts either, because as you say you want positive pressure on the valve cover went , not negative.</TD></TR></TABLE>

thank you, someone finally understands.

however, if you feel inside the factory intake arm...youll notice that there is a VERY slight "lip" where the hole is for the breather pipe to connect. it almost feels like an imperfection in the molding of the intake...like a leftover flap of rubber that didnt get trimmed off. but yes, the actual metal pipe isnt slash cut, but the rubber is molded on the inside of the intake arm so that it is essence a slash cut. the problem is that the rubber lip is very flexible and flimsy so at high vacuum levels it probably doesnt acheive the desired effect on the incoming air. what i have done is made my own slash cut piping that reinforces the rubber lip on the inside of the intake arm. hopefully it will work a little bit more efficently.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JOHN WAYNE &raquo;</TD></TR><TR><TD CLASS="quote">thank you, someone finally understands.

however, if you feel inside the factory intake arm...youll notice that there is a VERY slight "lip" where the hole is for the breather pipe to connect. it almost feels like an imperfection in the molding of the intake...like a leftover flap of rubber that didnt get trimmed off. but yes, the actual metal pipe isnt slash cut, but the rubber is molded on the inside of the intake arm so that it is essence a slash cut. the problem is that the rubber lip is very flexible and flimsy so at high vacuum levels it probably doesnt acheive the desired effect on the incoming air. what i have done is made my own slash cut piping that reinforces the rubber lip on the inside of the intake arm. hopefully it will work a little bit more efficently.</TD></TR></TABLE>


Since i have never seen what your talking about in a stock intake arm, i went and looked at 5 different intake arms; none have any kind of slash cut not even trying.
One of them have a little pretuding imperfection, but thats all it is and imperfection.

Main reason behind that is because you cant get the vaccum effect that a slash cut will give when trying to get positive pressure.

 

you will also notice that the inlet to the intake arm is at an angle....it doesnt make a perfect "T" with the intake arm. even if the little flap is an imperfection (i havent looked at any other intakes...) the angled inlet provides the slash cut effect.

if we can at least agree that a slash cut will move air INTO the head and not draw air OUT of it, then we're on the same page.

"positive" and "negative" pressure are relative terms depending on which side of the table youre on, so its hard to use these terms without explicitly saying from which viewpoint youre basing it on.

 

Wow, I just looked at several diagrams, I'm full of ****.

I've always thought it flowed into the intake. Sorry, I'm a tard.

So that does raise the question, why are we all sucking oil out of the head?? Why do we need a catch can?

my only theory now is that it is very slow moving air, and the cam is splashing oil up into the hose.. Sorry I doubted you man.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by phyregod &raquo;</TD></TR><TR><TD CLASS="quote">Wow, I just looked at several diagrams, I'm full of ****.

I've always thought it flowed into the intake. Sorry, I'm a tard.

So that does raise the question, why are we all sucking oil out of the head?? Why do we need a catch can?

my only theory now is that it is very slow moving air, and the cam is splashing oil up into the hose.. Sorry I doubted you man.</TD></TR></TABLE>

haha no worries...i think that mmuller is right about the intakes not having the slash cut. i just checked a GSR intake tube and it didnt have the "lip" inside...however, my ITR one definitely has a lip...could be an imperfection though.

regardless...according to the laws of fluid dynamics, you want a slash cut facing the incoming air to promote airflow into the head.

 

you do not want to try to ram the air in because it can build up in the crankcase and cause gasket failures and oil leaks, you engine will pull the oil and gas vapours out at the absence of pressure, vacuum.

Only thing you have to think about it how about if you are running a big cam and have little vacuum, now you not pulling the oil and gas vapour out quick enough.

One thing I can think of is that, a pcv system is a controlled vacuum leak.
One reason why you should always keep a pcv valve designed for a specific vehicle.
But I wonder if some testing can be done with different pcv valves and see which allow more flow. This could help draw out more vapours out of the crankcase. by causing a bigger vacuum leak.

Possibly fitting like a v6 pcv on a 4 cylinder. Obviously the 6 cylinder has more crankcase oils and vapour then a 4 cylinder but the same vacuum.

 

First discuss the oil residue in the intake which is prefectly normal for Hondas.

Basics: At idle when there is vacuum in the intake manifold and the PCV side is pulling vapor from the crankcase and the breather side (at atmospheric pressure) is feeding fresh air into the manifold. Just like in the diagram.


At wide open throttle the manifold goes to nearly atmospheric pressure while the breather is at atmospheric. In an ideal case the airflow would still be in the same direction (since there is still a slight pressure differential) however with the high pistons speeds and blowby we build pressure in the crankcase that the PCV valve side can't keep up with. The only other way to relieve crankcase pressure is the breather side hence the oil residue in the intake.

This is how it is designed from Honda... just a weak PCV system IMHO.

The slash cut will help 'push' air into the head since laminar (smooth) air flow in a pipe will move fastest in a tube in the center and be stationary near the wall. Use of a slash cut allows you to 'pickup' air in the middle where it's fastest moving and the highest pressure.... can't remember the formula but generally as velocity increases so does pressure.

But pressure in the crankcase is a bad thing for performance, extra pumping losses and what superdupervtec metioned.

Just put a clear hose on the breather and monitor the amount of oil going to the intake arm, should be only alittle bit ... if you get too much then you have a problem.

 

It is true that it is a recirculation system. At high vacuum (low rpm) the air goes through the pcv valve and is recirculated and burned in the intake manifold--while the valve cover sucks in fresh air from the intake, but at low vacuum (high rpm-open throttle) the pcv valve is pretty much useless but the crankcase gas has to go somewhere so it actually is PUSHED OUT of the valve cover and into the intake tube to be burned. I know in the service manual it only shows the first situation I described--but both situations are how the stock pcv system operates. Sometimes fresh air is entering the valve cover--and other times blow-by gas is venting through the valve cover--this has been discussed many times and this is what is happening. (the factory service manual only shows what is happening at low rpm, small throttle angles, high manifold vacuum in the diagram--they don't show what happens in a high rpm-open throttle situation--that is why people are always confused about this and debating it) Jay

 

i'm currently using the endyn breather kit instead of the stock PCV system. i really dont know how muh more efficient it is though.

with the endyn kit you can either let it use atmospheric pressure or use the vacuum from the intake manifold and a pcv valve (for emissions reasons).

would atmospheric pressure be more efficient than using vacuum?

 

The endyn kit is much better then oem, remember that oem is made for emissions.

The thing is when your doing high hp and are excluding emissions you do not care about our environment and care about your motor.

When your at wide open throttle, your pcv is closed because there is no vacuum to draw out the air and you do not want to push the intake charge into your block becuase it already has enough pressure created by your pistons, so the filter in the valve cover now becomes your exit and the gas exit's through there, what the endyn kit does is add an extra breather to help this get out, cause the higher you rev and more compression, and so on is going to cause more blow by, therefore you don't care for a slash cut cause the endyn just lets it out into the air.

The only time you would relly need a better pcv valve is if you have low vacuum and don't want blow by to stay in the crank case at low load, but it's the opposite when your racing at wot, just get it out, and the slash cut does nothing there.