Tests on the PCV system - How Honda intended it -

[dasher]

Over the years i have read much controversy over the stock PCV system and placing breather filters on the valve over. I have always wanted to test a stock Integra to get the facts straight and I finally got the opportunity to test this on a friends car. Here is a picture from the helms manual so you can see the how the stock PCV system is supposed to work - As you can see the airflow flows from the intake to the valve cover to supply fresh air. While the intake manifold supplies a source of vacuum to help evacuate the crankcase. When designing a PCV system on cars their is 3 considerations which are taken in 1) Performance 2) Emissions standards 3) Reliability Performance It is well known that performance gains can be had if the crankcase is under a slight source of vacumm which helps reduce crankcase windage losses. Many domestic users have seen decent gains by using either an electric or mechanical pump to help evacuate the pressure generated in the crankcase and even generate a vacuum present. Regaining lost power through the introduction of vacuum pressure evacuating the crankcase will not be as noticable on a small displacement 4 cylinder as compared to a larger displacement 8cyl domestic. Despite this, it should still be of importance to explore the various configurations and attempt to "free-up" any power hidden in our engines which can easily be tested on a dyno. Emmisions Standards and Reliabilty In order to comply with US emission standards honda had to use a closed PCV sytem which eliminated oil vapor from escaping into the atmosphere either from the valve cover or the crankcase breather. Oil vapors being introduced into our cylinders hurts performance and increases the probability of detonation occuring. The stock PCV system allows for the introduction of oil vapors into our intake manifold which hurts performance and reliabilty(a stock intake manifold is usually caked with collected oil and soot over the years). Is the stock PCV system designed with reliabilty in mind or merely to meet emission standards? Can we make our cars more reliable when we ignore emission standards and neglect the environment? Many attempt to trap some of the oil vapors being introduced into the engine by using either a catch can inline between the crankcase and intake manifold, a catch can inline between the valve cover breather and the intake, or both. I sometimes find it odd how people on the web will go on for years argueing and theorizing about the way in which the stock PCV functions and the intentions Honda engineers had when designing it. Knowledge and progress can only be obtained through keen observation and constant empirical tests... anything else is just wastefull. All these tests were conducted to measure the pressure differentiation between the valve cover and the stock air intake. It is already very well know the directional flow of from the "Crankcase-Crankcase breather-PCV valve- Intake manifold" path. The PCV valve acts as a check valve only allowing air to flow out of the crankcase and not in reverse. In a Naturally aspirated car the intake manifold provides a constant source of vacumm to pull air out of the crankcase. What we still need to tests is the pressure differentiation between the intake and the valve cover and how it behaves as a part in the system. Here we go with the tests: Car: 3 gen obd1 integra Engine: B18C1 Modifications: DC4-1 header, exhaust, (Stock Air intake!) The car was in great working order with good compression test + leakdown test #s. Testing tools: Calibrated Dewyer Magnehelic Pressure Gauge 0-5 psi range // Accuracy +-2% /// **************** Test 1 *********************** Tests were conducted in the driveway with the car in a nuetral gear with little to no load placed on the car. Testing methodology: The Magnehelic guage has a high and low pressure port to allow one to test pressure differences between two locations in real time. In the first test the low pressure port was connected to the Valve cover breather and the other port was connected directly to a stock intake as normally. In the second test I connected the low pressure port to the valve cover and the second port to a valve cover breather filter. In the tests data was recorded when the car was warming up and also recored at various different rpm levels when driving. The length of the hose was kept to a minimum to and from the guage. The length of the hose has no effect on the accuracy of the pressure readings and only effects the response quickness of the measurement. Results: The results for both trials were identical so the data will be shown together. idle warm up: 0.9 psi drawn into the valve cover idle operating temp: 0.8 psi drawn into the valve cover 2000 rpm: 0.75 psi drawn into the valve cover 5000 rpm: 0.70 psi drawn into the valve cover 8000 rpm: 0.65 psi drawn into the valve cover Analysis of the results: -At no load, you can see that the helms manual diagram is correct and their is a constant source of vacuum being drawn into the valve cover. -The pressure being drawn into the valve cover tends to drop slightly at WOT and higher rev ranges. -Using a valve cover breather did not impeed the breathing ability of the valve cover or change the results. -The stock Intake does not have a slash cut tube inside the intake for assistance of pulling air into the valve cover. It sits flush. Because it sits flush, the bernoulli effect attempts to pull air out of the valve cover, yet the vacuum source in the Valve cover overcomes this and still draws the air into the valvecover. Now for the more important test --- Load presented in a real life driving example and pressure datalogged. ************ Test 2******************* Testing conditions: Car was warmed up to normal operating temperature. Vacuum tubes were thread through the firewall hole into the cabin where i could monitor the pressure difference while driving between the valve cover and intake. Idle - 2K rpm... .75 to .8 psi vacuum into the valve cover. whenever I place any amount of load on my car the vacuum pressure dropped down quickly. 2nd gear pull to 4K rpm the vacuum pressure quickly dropped to .5 psi vacuum drawn into the valve cover. In 4th or 5th gear at 3-4K rpms I would quickly remove all vacuum present and noticed my needle went past 0 psi. Out of curiousity I then reversed the vacuum ports to read any pressure comming out of the Valve cover under load. Tests indicate that under load the pressure would shoot up to a maximum of .45 to .5 psi being pushed out of the valve cover. Even at half throttle at 3500 rpm in 4th gear the flow reverses blowing air out of the valve cover into the intake... this is not just an issue at WOT or high speeds... This is an issue when any fair amount of load is placed on the sytem. I conducted these tests over 30 minutes of driving in all gears. Unfortnately for safety reasons I was unable to rev past 5.5K rpm in any of the tests. /////////////////////////////////////////////////////////////////////////////////// Conclusions: - Engine Load effects the pressures in the PCV system. - The diagram in the helms manual is correct only at idle and low load conditions. - Load placed on the engine forces air to flow both out of the valve cover and out of the crankcase into the intake manifold. Thus the flow reverses from vacuum being drawn into the intake manifold to pressure forced out. Before I give my opinion on the implications of the results on: 1) Valve cover breather Filter- helpful or harmful? 2) Stock Honda PCV system- designed for reliabilty, emmisions, or performance? 3) In terms of reliability and performance how should a NA PCV system be setup? 4) In terms of reliability and performance how should a FI PCV system be setup? I welcome everyone else to first share their thoughts on these matters before I give my opinions. I welcome any discussion or critism of my tests but please criticize the testing methodology or my analysis of data in a logical manner since I carefully spent the time to gather these results. PS- stay tuned! when I have time I'm going to run several tests on the advantages/disadvantages of various different PCV systems on a Turbo car and test the results with the Dewyer gauge and test any performace gains which can be obtained(tested on a dyno). Modified by dasher at 12:03 AM 12/6/2003

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[Johnyquest]

I've said it from day one. The only reason the thing is hooked to the intake is to

A) Draw fresh FILTERED air in when the valve cover is @ vacuum.

B) Push crankcase vapors BACK into the motor to AVOID POLLUTING.

From this, and your test, I conclude, as I always have:

Replacing the 'hose' with a filter doesn't effect anything besides stops the feeding of blowby gas into your intake again... Which, as stated, can cause detonation and other problems.

[dasher]

I'm going to hold off on my personal opinions at this moment to allow a more hospitable environment for free discussion.... but here are some things to think about in the mean time.

Some of the differences between using a breather filter and plumbing a tube from the valve cover to a source of vacuum like and intake are -

1) A breather Filter will not assist or resist(neglecting the minimal frictional losses through the filter) the flow going into or out of the valve cover.

2) The bernoulli effect of the flush opening in the intake tract resists the vacuum drawn into the valve cover at low load situations and when load is introduced the intake will assist to draw air out of the valve cover.

How does this effect our cars?

[Muckman]

My only question about thise system is whether a vaccuum source has a positive or neutral effect on the system. Will the PCV work as well as stock without a vaccum and being vented to the atmosphere?

[Ri5e]

Excellent research!

Here is what I think:

On a boosted Honda, the PCV Valve system is pointless when there is no vacuum in the manifold or positive pressure.

1. The valve cover breather filter is harmful in a boosted Honda because all that pressure in the crankcase is trying to force itself out of the little hole in the valve cover. This may cause cam seals or such to blow out quick. The best way to overcome this is to drill two more holes in the front of the valve cover and add fittings/hoses to let this pressure escape faster. Or on the back of the block, there are two plugs that you can undo and put in a brass barbed fitting and run hoses to a catchcan. (Either run it open or close loop)

2. The stock PCV system allows for both reliability (less wear on the seals) and serves as an emissions purposes (Lets the blow by gases flow back into the system so the air doesn't get polluted). As for performance, at WOT the stock PCV doesn't do anything put spit out blow by gases

[dasher]

or wether the pressure drawn created by the bernoulli effect is so small that it is negligable is another thing to consider.

[dasher]

Turbocharged cars do tend to have more blowby... so opening up several other openings in the front of the valve cover does look promising... I have seen it done on Larrys car at endyn, AEBS race car, and my own to name a few.

At WOT the PCV valve is closed... is this a good thing?

[Ri5e]

Also on the OBD2 Integra valve covers, the breather AND the PCV valve is located on the valve cover whereas on the OBD1 Integra engine, the PCV valve is behind the block and the valve breather is on the valve cover. I wonder why Honda did this??

[highmilehatch]

This is really good stuff. I commend you for doing such research. I've personally come to the conclusion that the best pcv setup on a FI Honda engine is no pcv setup. Does anyone know where to get those brass plugs that will thread into the back of Honda blocks?


Modified by highmilehatch at 10:33 AM 12/5/2003

[hooohaa2]

Great research. I would also like to know about these plugs.

[Adi Radoncic]

First I wanna thank dasher for bringing up this topic and doing research on it so we all get a better understanding of what really happens with the pcv system and its gasses..

With that said I just wanted to ask a qestion.

From the write up you did I got the basic understanding that for a pcv system to work properly and to suck out as much harmfull gas out it has to have vacum to pull it out. So why not just take a catch can drill an extra hole into it on the top somewhere, filter that hole than drill another hole into the intake pipe on your turbo and connect the vacum line from there to the catch can.

Than just hook the catch can back up as normal. By doing that I'm thinking that with the extra vacum pull you can suck in way more crap coming out of the motor than by just hookin up two lines to a can.

This is just a shot in the dark and I'm open for any suggestions, creative comments.

Again, thanks for the write up..

Adi

[xenocron]

Gotta love the TECH in Honda-Tech here.

One question...on an NA honda engine, whether idle or at any RPM level...is the intake pipe ever under vacuum? Could you hook up a Vac/Boost guage to the hole where the valve cover breather connects and see a reading other than 0? Load/No load?

Interesting that it "switches" under load. Any indication at what RPM/load that point is where it switches? Does it change?

I think the PCV system was designed for lower load, non high RPM driving (which is what most mainstream purchasers and users of factory vehicles are doing)

Also, is there any implications of VTEC vs. NON-VTEC when it comes to the high RPMs/load and switching of the low to high profile cams?

They have iVTEC, next is iPCV!

[dasher]

The easiest and most trouble free setup would be to slap a filter on the valve cover and a filter on the crankcase and vent to open atmosphere on a Forced Induction car .. no doubts in that .. But is this really the best setup?

From a performance standpoint and an emisions standpoint ... no.

[T4sol]

Originally Posted by dasher

From a performance standpoint and an emisions standpoint ... no.

Why no on a performance standpoint? Crankcase pressure is reduced.... Is vacuum more desireable?

[highmilehatch]

I've been thinking about what you mentioned on the performance aspect. I'm curious if there is a significant amount of power loss due to the absence of vacuum in an atmosphere-ventilated crankcase. Lets say you have a 2.0 liter 4 cylinder FI engine that would lose maybe 5 hp max if there is no vacuum to help the gases out, and would regain that power by using vacuum. I would definitely trade that 5hp for a properly ventilated FI engine, granted there were no other negative effects. If it were 20 or so hp, I would then put some thought into coming up with a way to get vacuum on the crankcase. However, my other concern is piston ring wear. I'm curious if there is any concrete evidence of faster ring wear on an engine that has an open atmosphere setup with no vacuum, as compared to one with. Hmmm. This is good stuff. Keep it coming guys.

[dasher]

creating vacuum present in the crankcase has proven to reduce power robbing windage ... domestics have shown noticable gains in power with a properly setup PCV system evacuating the crancase (by either mechanically or electric vacuum pump) -- the gains would not be as much with a smaller displacement 4 cylinder engine but I am going to enventually test this on a dyno.

As far a reliability concerned ... I would assume that a properly setup PCV system will allow rings to seat better... this needs to be tested however...

[b18cx]

This might sound dumb, but I thought I would through it in the mix. I think some of the Domestic's have done this but not for sure.

Why not use the exhaust as the source of vacume??? Take a small tube, weld it in at a 45 degree angle pointing in the driection of the exhaust. Would this not help creat a rpm dependat vacume??




Modified by b18cx at 11:57 PM 12/5/2003

[dasher]

That is one setup which I'm going to actually test using a slashcust tube welded in the downpipe to provide a source of vacuum.... some experimentation is going to be needed to get the correct size port so it draws the right amount of vacuum. Don't forget to place a checkvalve inline on the line also.

There are some problems with this ... you can foul your o2 sensor or cat if too much oil vapor is drawn through ...

[SlowTeg]

Just a question regarding your setup..

For the extra ports you have on your valve cover, do you simply just have little breather filters on them or do you run them all to a catch can as well?

Have you tested different breather "setups" to compare if there's actually reduced pressure in the crankcase under load? I'm just curious if you've messed w/ say a car w/ the stock pcv in place and a valve cover breather versus say the endyn setup where the plugs are removed and used to vent more, or a valve cover w/ more vents.. Thanks. Great research!

-Mike

[tommyten]

When I was looking at Norris P. (not sure how to spell his last name) All motor race car, I noticed he had a tube running from the valve cover port to his exhuast. Maybe he knows something we dont

[XDEep]

did you not test the pressure on the crankcase hose w/o the pcv?

i didnt like how theres no vacuum and the crankcase vent is closed, so what i was going to do was leave the pcv system in place, however tap the crankcase-to-pcv line with a one way check valve. this way, the pcv would still provide vacuum, but when in boost and the pcv shut, the one way check valve would allow vapors to escape.

also, if you could test the pressure after the pcv valve, this will tell us if the crankcase pressure is enough to blow past the valve w/o the intake's vacuum. if so, we know the pcv valve was designed to not fully close shut at WOT. each pcv for each car is designed with a specific weight on the plunger to allow vapors to vent at a specific rate.
and also if there is venting at WOT, you could just use a 2nd pcv valve instead of a check valve to simulate an NA motor when in WOT and boosted.

btw, it should be noted that not only can air be blown up through the pcv valve with enough pressure, but if you are to mount it somewhere else its imperative it remains as vertical as possible. at i think a 30* angle or more, boost can make its way past the plunger.

[LiLOtaku]

Originally Posted by b18cx

This might sound dumb, but I thought I would through it in the mix. I think some of the Domestic's have done this but not for sure.

Why not use the exhaust as the source of vacume??? Take a small tube, weld it in at a 45 degree angle pointing in the driection of the exhaust. Would this not help creat a rpm dependat vacume??





Modified by b18cx at 11:57 PM 12/5/2003

If you need a constant source of vacuum, why not just tap right back into the intake on a turbo compressor(for FI'ed cars). I'll be having my setup look very similar to this excpet my vacuum line will be tapped into the intake fliter tube on the turbo.

[SlowTeg]

Ya it seems like a good idea, but I guess the big problem would be pulling the oil vapors into the intake for the turbo and then having them go back into the combustion chamber. If you use the exhaust as your vacuum source, the vapors will just get dumped w/ the exhaust.

-Mike

[HXMan]

Bump, good post!

[dasher]

Ok guys lets go through some basics.

Purpose of the PCV system
During each compression stroke a small amount of gas seeps past the piston rings. These gasses comprise of an unburnt fuel/air mixture which contaiminates your engine oil and corrodes your internal parts. The purpose of the PCV system is to remove these gasses while maintaining emissions standards.

The PCV valve tested is known as a variable-flow PCV valve. This valve allows the crankcase to evacuate gasses into the intake manifold even at high load conditions.

The problem Honda engineers had was the following:
They needed to find a vacuum source which provides a variable vacuum with less draw at idle and more vacuum pressure pulling gasses out at high load (WOT) conditions. The dilemma is that at Idle and low load conditions the vacuum present inside the Intake manifold is the greatest and at WOT the vacuum in the intake manifold is the lowest(almost none). This is the exact opposite of what is needed because their is more blowby gasses needed to evacuate at WOT (high load) then at Idle!

So they designed a special spring loaded pintle valve(PCV valve) which does the following:

Idle, Low load--- high vacuum pressures fully retract the pintle causing only a small vacuum draw on the crankcase.

Mild load conditions--- vacuum present in the intake manifold is not as strong so the pintle sits in the middle of the pcv valve allowing more vacuum to evacuate the crankcase.

High load + WOT conditions--- their is almost no vacuum present and the pintle is almost completely extended allowing the most amount of gasses to be drawn into the intake manifold.

Engine backfire--- the pintle fully extends and seals to eliminate any gasses from flowing from the intake manifold to 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.