I know catch cans have been covered a thousand times but I had some ideas about one. I've seen the posts where people replace the black breather box on the back of the block with a plug and use those fittings for the 2 freeze plug holes.

But, I'm building a mild 1.8 build. Nothing extraordinary. 185-190hp to the wheels is all I'm looking for. At this point I'm undecided as to what I want to do for a catchcan. I don't want to run a catchcan/breather because I want to keep my system closed loop and for now I want to keep that black breather box. If I was running a 2.0L NA or turbo I would for sure run the Endyn style cathcan/breather and tap into the plugs on the back of the block and ditch the black oil seperator box.

But, there are problems with the stock PCV system that I want to address.

During low/medium load the system works just like it's supposed to. The PCV valve going to the IM is closed or only open a very little to create vacuum. The breather on the valve cover is pulling in fresh air into the crankcase via the vacuum that is created with the PCV closed. Show below: (please excuse my pics)



Then under high load/WOT bad stuff starts to happen. There is almost no vacuum present, the PCV valve is completely open to the IM to allow all the pressure that's building up to escape the crankcase. Under acceleration and high load situations blowby is extremely high and consequently the PCV valve/purge hose cannot supply enough vacuum to remove all the gasses needed. This is when the flow reverses from the valve cover to the intake. Their is so much blowby present that both the PCV valve/purge hose and the Valve cover breather/hose have to both vent excess pressures created. The PCV is working at its best but can't keep up with the demanding pressures created. This is bad because now we have oil vapors from the valve cover going INTO the intake stream as well as some oil that's present going into the IM from the PCV. The black box is supposed to seperate it but I don't know how good a job it does. This is what causes all that gunk inside the throttle body. See below:



So, I thought about this and wasn't sure what to do. Well, I know I want a catchcan setup and I want to keep the stock black breather box. So here is how I would setup my catchcan system. Basically, the catchcan would be inline between the black oil breather box and the IM. The PCV valve would be moved to the catchcan. The breather from the intake tube to the valve cover would remain there. So, this is my catchcan setup and is showing what's happening under low load:



Now, we still have the same problems we did before under high load/WOT situations. The PCV valve is fully open and cannot handle all the pressure building up in the crankcase. So now the breather tube from the valve cover to the intake tube reverts and is venting out pressure into the TB. So, we've seperated the oil out of the stream of air going from PCV to the IM, but now the valve cover has reverted and is putting oil/air mixture right into the TB. This is effectively lowering the octane of our gas mixture now that oil is present not to mention making a mess of the TB and IM. See below:



So, in light of that this is what I'd like to do. I don't want to use the plugs on the back of the block and I want to keep my black oil seperator box in place. I don't want a breather setup because I want to keep it closed loop. Keep all that in mind when looking at this. Now, what I want to be able to do is under high load be able to have an extra place for the crankcase pressure to escape. But I don't want just a dumptube somewhere because at low load I want the engine to be able to create vacuum like honda had intended it. So, I would tap another line into the valve cover and route it to the catchcan, but I would put a check valve on it so it's only open under high load. I would tap another spot on the IM to add another tube to enter the IM from the catchcan and that would also have a check valve on it so it only opens under high load. The only thing I am not sure of is exactly how check valves work. Are they normally closed and then under high pressure they only allow air to pass 1 way? Or are the always open but only allow air to pass 1 way? What I want is something that is normally closed and only opens under high pressure and only lets air flow 1 way. Maybe PCV valves would be better there. I have to look into check valves more.

See below of what I'm talking about:



I know it looks hokey but I think it would work quite well and I had a lot of criteria that I had to meet and I think this fits all of it. Also, you could put another 1 way valve on the valve cover breather to the intake tube so only air is allowed to enter the valve cover. When it's under high load the excess pressure can go out thru the other hose that's tapped into the valve cover.

Thoughts? Suggestions? I am going to try some variation of this. I'm just not sure what yet.

s

 

just subscribing.

 

My suggestion would be to use a different vacuum source (ie: electric vacuum pump or exhaust evacuation) and dump the vapor contents into a catch can, or out the exhaust.

This way you can get negative pressure throughout the crankcase system all the time.


Modified by IN VTEC at 3:10 PM 1/30/2004

 

The below illustration is also a bit untrue.

With no open path to the intake manifold, there is no vacuum. There is, however, a bit of positive crankcase pressure pushing the vapor into catch can, but with none or insufficient volume to displace, it'll eventually back up. Same scenario as with the stock PCV valve placement.



You need one more one-way check valve for the tube coming from the intake pipe to the valve cover to more completely isolate the crankcase system from the intake system.

 

Larry from Endyn's simple sollution is to use a slashcut tube in the intake to route air into the valvecover even under high load. The difference in pressure between the crankcase and the vaccum line on the PCV valve should cause the valve to open and bleed off the excess pressure.

The problem with the last drawing is the flow can still revert (as I think you said). But putting a one way check valve is just going to prevent any positive ventilation at WOT. (It is called positive crankcase ventilation for a reason )

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">The below illustration is also a bit untrue.

You need one more one-way check valve for the tube coming from the intake pipe to the valve cover to more completely isolate the crankcase system from the intake system.
</TD></TR></TABLE>

yup, read it all. i covered that.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">The below illustration is also a bit untrue.

With no open path to the intake manifold, there is no vacuum. There is, however, a bit of positive crankcase pressure pushing the vapor into catch can, but with none or insufficient volume to displace, it'll eventually back up. Same scenario as with the stock PCV valve placement.
</TD></TR></TABLE>

hmmm, you sure? why isn't there vacuum? pressure is building up in the crankcase but the PCV is closed because it's not enough to open it.

s

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StyleTEG &raquo;</TD></TR><TR><TD CLASS="quote">Larry from Endyn's simple sollution is to use a slashcut tube in the intake to route air into the valvecover even under high load. The difference in pressure between the crankcase and the vaccum line on the PCV valve should cause the valve to open and bleed off the excess pressure.

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

yeah, but at WOT there's enough pressure that it's still getting pushed out that tube anyways.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by StyleTEG &raquo;</TD></TR><TR><TD CLASS="quote">
The problem with the last drawing is the flow can still revert (as I think you said). But putting a one way check valve is just going to prevent any positive ventilation at WOT. (It is called positive crankcase ventilation for a reason )</TD></TR></TABLE>

it's not designed to flow out the valve cover. at least you don't want it to anyways. That's what the hose from the block to the PCV to the IM is for. That's the postive ventilation.

s


Modified by stevel at 7:05 PM 1/30/2004

 

The intake manifold is your source of vacuum. If there's no open path to the manifold, then there's no vacuum draw.

If the PCV valve is closed, then so is the path to the intake manifold.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">The intake manifold is your source of vacuum. If there's no open path to the manifold, then there's no vacuum draw.

If the PCV valve is closed, then so is the path to the intake manifold.</TD></TR></TABLE>

so at idle is the PCV normally open or closed?

s

 

At idle, it's open. 520 to 540mmHg ~ 20" to 21"Hg of vacuum in the manifold at around 800rpm.

A PCV valve is just teh same as a one-way check valve. It only allows flow in one direction...towards the manifold.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">At idle, it's open. 520 to 540mmHg ~ 20" to 21"Hg of vacuum in the manifold at around 800rpm.

A PCV valve is just teh same as a one-way check valve. It only allows flow in one direction...towards the manifold.</TD></TR></TABLE>

ok, now i'm confused. so is it still open at WOT? when does it close?

how is the PCV valve open during idle/low load? don't you need vacuum in the crankcase to pull the valve shut?

s


Modified by stevel at 6:53 PM 1/30/2004

 

Crankcase vapor increases as a function of load, so you'll need PCV more when you're driving hard. At idle, theoretically, you don't need as much PCV.

The Honda PCV is a downward facing plunger with a check spring behind/on top of it.

The two ways the PCV valve works is that positive crankcase pressure will push the PCV valve open, and high vacuum will pull the PCV open.

At high load conditions:
-The crankcase pressure will hold the valve open off the bottom seat even if the vacuum from the manifold is insufficient, but there's almost always gonna be some vacuum from the manifold in a NA engine.

At atmospheric pressure:
-The plunger doesn't appear to seat against anything, so even under high load (close to atmospheric), crankcase vapor is still allowed to push its way towards the manifold.

No load, really high vacuum:
-The plunger is pulled by manifold vacuum closer to the upper seat. The upper seat doesn't completely seal b/c it's not a full-faced seat (it has chunks missing out of it), so even under high vacuum conditions, some crankcase vapor still makes its way to the manifold...just not as much.

The only time the PCV valve is completely shut is if the manifold sees enough positive presure to force the plunger down against a fully-sealing seat. Positive pressure in the manifold from supercharging or backfires in the manifold will cause the valve to shut.

----------
A flaw I can see with the PCV valve is that if there's too much positive crankcase pressure, it'll push the plunger all the way up into the upper seat, which will partially restrict the flow and only push it even harder into the upper seat and hold it there.


I can post pics of the PCV valve I thrashed if you wanna see the plunger and upper/lower seats.

 

cool. thanks for the info.

so does my system seem pretty good? what changes would you make?

also, I'm not sure what you mean by what is below? The way I have the catchcan rigged up is pretty much the same as stock. I have just moved the PCV valve. Do you agree? I don't know what you mean by saying it'll backup from no open path to the IM.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">The below illustration is also a bit untrue.

With no open path to the intake manifold, there is no vacuum. There is, however, a bit of positive crankcase pressure pushing the vapor into catch can, but with none or insufficient volume to displace, it'll eventually back up. Same scenario as with the stock PCV valve placement.
</TD></TR></TABLE>

I'm not doubting what you're saying I just don't know and am confused.

s

 

I have two questions.

Please explain why you say you don’t want to run a catch can/breather because you want to keep your system in closed loop.

Also what if you ran a hose from the valve cover and the black breather box to the same catch can and this catch can had a breather filter on top of it? Is this an incorrect way to setup a catch can?? Now you would not be pulling in any vapors into the intake manifold. I’m just wondering if you would end up pulling vapors into the valve cover from the black breather box or would you just be pulling in air threw the breather filter on top of the catch can??

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MadtownSi &raquo;</TD></TR><TR><TD CLASS="quote">

Please explain why you say you don't want to run a catch can/breather because you want to keep your system in closed loop.

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

When you put a breather the oil vapors are venting out the breather to atmosphere. Now it's open loop.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MadtownSi &raquo;</TD></TR><TR><TD CLASS="quote">
Also what if you ran a hose from the valve cover and the black breather box to the same catch can and this catch can had a breather filter on top of it? Is this an incorrect way to setup a catch can??
</TD></TR></TABLE>

that's a breather/cathcan setup. It's more than a catchcan.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MadtownSi &raquo;</TD></TR><TR><TD CLASS="quote"> I'm just wondering if you would end up pulling vapors into the valve cover from the black breather box or would you just be pulling in air threw the breather filter on top of the catch can??
</TD></TR></TABLE>

i don't know either.

s

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">VACUUM PULLS OIL VAPOR IN WHICH GETS SEPARATED BUT PCV VALVE STAYS CLOSED.

NO AIR COMING IN BECAUSE PCV VALVE IS CLOSED</TD></TR></TABLE>
The two statements contradict themselves. The illustration is fine, but the captions are not.

Edit: I'm sorry, only the first contradicts itself...the second is redundant in my point.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">
The two statements contradict themselves. The illustration is fine, but the captions are not.</TD></TR></TABLE>

cool. thanks.

s

 

IN VTEC,

I would like to see the pictures of the PCV valve. I have wanted to dissect one, but the stock ones are rather expensive, and I couldn't find one in the junk yard last time I went.


stevel,

Exactly what are you trying to accomplish?

The stock system does reverse flow and some vapor flows out the intake tube connection at high load & rpm. The two vents (the IM and intake tube) are enough to relieve this pressure, so another vent is not necessary. I am speaking about a stock to basically stock motor. The PCV valve connection alone will not flow quite enough by itself under high load/high rpm.

Are you just wanting to use one separator for both lines? Your system with or without a check valve in the stock connection to the intake tube is just like running without a PCV valve - major vacuum leak. If you run the intake tube connection through (and it would have to be through not TO, as the PCV itself does not flow enough), then at high load you would have the benefit of increased separation, but at lower load and high vacuum, the crankcase would not be kept as clean because the fresh air flow through it would be less.

The stock system sucks dirty air out from the bottom and clean air in through the top except under high load & rpm when both connections become simply vents, there is no fresh air flow. Running both connections to the catch can would change this flow up.

The best way to keep it closed and maintain proper clean air flow which helps keep the oil clean and is important in a street car (most discussions leave this function of the PCV system out) is to run two catch cans. I think this might be overkill for the street as only very seldom does any flow go out the intake tube connection. Most of the time it is only through the PCV valve connection, and this is where the separator will be most effective.

I am going to test and see if restricting the size of the intake tube line will allow for vacuum to be built up in the crankcase instead of atmospheric pressure most of the time and will still allow enough flow out under high load and rpm to prevent pressure build up. If the intake tube connection flow is reduced, the PCV valve side should pull more air and create a slight vacuum under most conditions. This might not work however, as this connection is needed to vent under high load & rpm conditions. Yes, I have tested this.

Yes, this will also decrease fresh air flow, but will still allow for some. The flow rate in will just be somewhat less than the flow rate out. Well, that's the theory anyway. I have got to test it.


Modified by kelly at 9:43 PM 2/17/2004

 

Oops. I already tossed it. I'll doodle you one.

 

expensive? they're only like $5 or so at autozone.

just to keep the TB and IM clean from oil going in and from leaning out the effective octane of the gas.

exactly. the one to the IM is made to go in both directions but the valve cover to intake gets everything really dirty when it reverses flow and goes out of the valve cover instead of into it.

yes, just one catchcan

why is this a major vacuum leak? it's a source for it to pull vacuum and that's how it was designed as stock and that's the way i'm leaving it. but i want a check valve there so it only goes into the valve cover and doesn't revert. I want it to revert out a different tube that goes thru the seperator.

yes, it does revert back out under high load. But it's not really designed that way and that's exactly what I don't want because that air is not seperated and has oil in it also which gets everything dirty inside and lowers the octane of the gas mixture.

i don't see how this will be any benefit. I don't see any problems in the engine building up vacuum under low load. And it will just cause more high pressure in the crankcase at high load. I think it might make matters worse.

this doesn't make any sense to me. In the most common ways catchcans are mounted (basically inline between the pcv valve and IM) it's just an extra oil seperator and the lines still come from and go to the exact same place in end.

i want to address the valve cover to intake tube reverting and make it so it only goes 1 way and when it tries to revert I will provide it with another outlet for the pressure that does go thru the oil seperator.

s

 

IN VTEC,

Thank you.

stevel,

I wanted to see what the Honda valve looks like. The aftermarket ones might not be the same, and I don't trust that they are.


I do understand what you are trying to do. I have had many discussions about the PCV system and know that it is very difficult to discuss because there are so many variables, so I am going to stay with one point for now.


Your system runs a connection to the intake manifold with a check valve parallel to the PCV valve connection. This connection effectively bypasses the PCV valve. The check valve will open when it sees a pressure differential across it which will be practically all of the time. I will simply stick to idle conditions for now. The check valve will see atmospheric on the crankcase side and high manifold vacuum on the other and will be wide open. However, unlike the PCV valve, it has no metering valve, so it will just be a wide open vacuum leak.

 

Learn alot from this post

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kelly &raquo;</TD></TR><TR><TD CLASS="quote">

Your system runs a connection to the intake manifold with a check valve parallel to the PCV valve connection. This connection effectively bypasses the PCV valve. The check valve will open when it sees a pressure differential across it which will be practically all of the time. I will simply stick to idle conditions for now. The check valve will see atmospheric on the crankcase side and high manifold vacuum on the other and will be wide open. However, unlike the PCV valve, it has no metering valve, so it will just be a wide open vacuum leak.</TD></TR></TABLE>

ahhh, i see what you're saying. so what would be a solution? use PCV valves instead of check valves?

s

 

You added another line to your system because the stock system can't flow quite enough through the PCV valve connection under high load & rpm conditions and forcing the valve cover outlet to also go through the separator would mean that unless another outlet was added, all the flow would have to go through the PCV valve, correct?

The problem is that now this connection needs a metering valve also. So now you are back to the factory set up but with two PCV valves instead of one and more complication. The two PCV valves would have to be changed and would end up with the same flow potential of the one stock valve.

Get a vacuum/pressure gauge and connect it directly to the valve cover outlet and drive the car around. You will see that the factory system is very good. You might get 1/2 psi after a full throttle pull to redline from 1st through 3rd gear. So this means there is very little reversion (this does not take into account the slight vacuum produced in the intake tube - this is more of a test of the flow rate of the PCV valve side of the system). Mine will pull about 6 inches of vacuum the rest of the time. At 6 inches something starts leaking. It sounds like the front main seal. The engine will maintain this level and will dip lower, but last time I did this (yesterday) I could not get the pressure to go positive. After you do this, connect the gauge directly to the intake tube side and see what happens. Then if you want, you can connect the gauge with the system fully functional. Now you will have a better idea of exactly how good or bad the system is.

There are other problems with your setup. The best/simplest way is two separators, although the second separator is pretty much overkill which you should see when you test. Your vehicle could well be different. All my tests were on my '99 GS-R with the factory PCV system and 57,000 miles on the well maintained engine. I have I/H/E/C/TB/ITR intake cam, nothing major.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kelly &raquo;</TD></TR><TR><TD CLASS="quote">You added another line to your system because the stock system can't flow quite enough through the PCV valve connection under high load & rpm conditions and forcing the valve cover outlet to also go through the separator would mean that unless another outlet was added, all the flow would have to go through the PCV valve, correct? .</TD></TR></TABLE>

right. another outlet was added to the valve cover to aid in relieving the extra pressure that's built up under high load and similarly another inlet into the IM to complement the extra out.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kelly &raquo;</TD></TR><TR><TD CLASS="quote">

The problem is that now this connection needs a metering valve also. So now you are back to the factory set up but with two PCV valves instead of one and more complication. The two PCV valves would have to be changed and would end up with the same flow potential of the one stock valve.

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

you got me confused here. I would add another line out of the valve cover to the seperator that I mentioned above but I would also add another line out of the catchcan to the IM. I don't see how we're at the same flow potential of 1 valve.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kelly &raquo;</TD></TR><TR><TD CLASS="quote"> You will see that the factory system is very good. You might get 1/2 psi after a full throttle pull to redline from 1st through 3rd gear. So this means there is very little reversion (this does not take into account the slight vacuum produced in the intake tube - this is more of a test of the flow rate of the PCV valve side of the system).
</TD></TR></TABLE>

The stock system is pretty good until a high load situation. Reversion in the pcv valve? I agree there's probably little to none there. It's trying to vent the crankcase but is overwhelmed at WOT. But the valve cover intake tube definitely reverts. You ever look in your throttle body? All that black junk is from the valve cover intake tube reverting.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kelly &raquo;</TD></TR><TR><TD CLASS="quote"> Now you will have a better idea of exactly how good or bad the system is.

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

I had a stock GSR also and from looking into my TB after just 15,000 miles I was convinced it needs some modification.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kelly &raquo;</TD></TR><TR><TD CLASS="quote">There are other problems with your setup. </TD></TR></TABLE>

like what? I'm not doubting you, I just want a solid design. I want to keep the stock oil seperator, add a catchcan, keep the valve cover to intake tube and still be able to solve the reversion problem under high load and provide another out for the high crankcase pressure. Help!!

hmmm, maybe i'll just do a second catchcan for the valve cover but that will be a breather.

s