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 Post subject: catch cans and blow by
PostPosted: February 10, 2019, 8:10 pm 
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it must be true because its on youtube.

whats that, you agree?

man i have never heard such a load of uninformed nonsense in my life.

none of these people seem to understand what is causing oil vapors to collect in the intake tract in various places.

PCV systems work in two ways, first the PCV valve, this is only open when there is a vacuum in the intake sufficient to pull the valve open and if not it will be closed. the second way is as a flash arrestor to prevent an explosion in the intake from traveling back to the crankcase and igniting vapors that may be present.

in addition to this PCV line, most if not all engines must have a way of supplying additional air to the crankcase so that flow can occur like a valve cover vent, this will allow the PCV pipe to remove vapors and replace them with fresh air.

modern engines use a system called make up air, this is a system that draws air from the inlet tract upstream of the throttle body, on speed density engines this is drawn from the air box on the down stream side of the filter giving clean air to the system. on MAF engines it is installed in the intake tract down stream of the MAF but upstream of the throttle body so that the MAF sees this air and can fuel the engine accordingly, speed density uses the fuel tables to compensate for this in conjunction with the MAP sensor.

here is where we run into a problem, what happens if the throttle is opened wide? well the PCV shuts so air flow through the crank case stops.

unfortunately turbulence in the crankcase does not and blow by is present, these two things are present in all engines but there is no way to remove them.

in a speed density engine this blow by together with oil vapors present in the crankcase find the least path of resistance to escape which is the pipe for make up air sending the pressure and oil vapors to the filter box, as we are at WOT the pressure in the box is below atmosphere due to the draw of the engine, no vacuum but flow is present so the vapors and gasses are drawn through the intake tract to the engine.

in a MAF system a similar situation applies but the crankcase is vented into the runner where it is again sucked into the engine, the problem is how much of this is air, as everything that gets into the engine has been metered including make up air, but now we are in a state where make up air does not exist.

no make up air equals no flow through the crankcase, so where is all the pressure coming from? answer, blow by.

is this good or bad, the reasons for blow by in a good engine as opposed to one that is worn out can be defined in one term, ring seal, in modern engines piston rings have had their tension reduced due to fuel economy over parasitical losses and now we are teetering on the edge of a blow by cliff, to push us over the edge is the ever present danger of crankcase pressure, this has a detrimental effect on ring seal due to the narrow nature of these low tension rings causing flutter.

well that's it then we are screwed and every time we hit a WOT the pressure rises forcing the creature from the black lagoon into our intake and oil to spew from every orifice.

well not quite, if we can do something about crankcase pressure at WOT, if we vent the crankcase to atmosphere with suitably large vents, i revert back to a time in the distant past when i ran a triumph twin on fuel and a blower, a blow by nightmare if ever there was due to the windage of two pistons going up and down together combined with the quantities of fuel and a blower raising the combustion pressure, nitro is an oxygen rich fuel requiring virtually no air to keep the motor running at idle,
on a 750cc engine we would run a breather to atmosphere of 1-1/2"" diameter and still place it opposite the magneto to stop oil passing the seal, this would maintain crankcase pressure to atmospheric.

so you can see that to vent a car engine to atmosphere would require a lot of ventilation if it was predisposed to blow by by design.

so to recap as you can get lost in all of this,
BAD
blow by bad, oil in the intake causing unstable mixtures bad, oil leaks past seals bad, oil in the combustion chamber causing detonation bad, oil on the intake valves bad, oil on the throttle plates bad and crankcase gasses in the intake charge taking the place of air
GOOD
high crankcase pressure helping the oil pump to lift oil from the pan good oil vapors wizzing around in the crankcase to lubricate the wrist pins good, oil lubricating timing chains good

this brings us to the real story,
we need oil vapor in the crankcase, we need oil that can absorb the contaminants of blow by without degrading between oil changes, we need a good filtration system to remove particulates of combustion, what we don't need is the oil escaping from the crankcase in the form of vapor, we need a slight vacuum in the crankcase to promote ring seal and to reduce oil leaks and no atmospheric breathers throwing oil all over the place.

VAC-U-PAN, via closed oil breathers on the valve covers connected to a check valve/flame arrestor which in turn is placed in the exhaust to extract the gasses and any vapors that are not captured by the breathers, alas these only seem to work with open headers as you can't expect them to suck if there is back pressure in the exhaust due to mufflers or cats, on race cars o.k. i have used them with success.

so catch cans i here you say vented to atmosphere, this would help some but you only get atmospheric at the best in the crankcase and we need a negative pressure for ring seal.

this leaves us but one option, we must suck the pressure out of the crankcase via a catch can which drains the oil back to the pan where the remaining oil can absorb the included contaminants. and vent the gasses extracted to atmosphere, the only thing to worry about is what oil and how long will it last between oil changes.

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PostPosted: February 10, 2019, 8:31 pm 
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Seriously? Vacuum in a properly tuned crank? (taking notes)

Of course, you could run 2-cycle oil in your crank which would burn better as excessive blowby covers everything w/ oil... and on a worn out motor, you're not gonna run it long anyway... (grins)

BTW, full syn oil kinda smells like burning hair when it leaks out to something hot?

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PostPosted: February 11, 2019, 1:18 am 
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I read partially your post so bear with me.
PCV stands for Positive Crankcase Ventilation. Therefore what opens the valve is not Vacuum in the manifold, but pressure on the crankcase.
Although on second read, it may be the same thing.... Differential pressure...
salud!!


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PostPosted: February 11, 2019, 3:50 am 
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The PCV valve on a naturally aspirated engine should actually be opened to the maximum flow position at WOT, if properly selected, and is most certainly not closed. This is why the 'correct' answer is exactly what OEM's already do, which is route the line out of the oil separator (catch can) back to the intake/vacuum manifold. If there are other conditions causing an excess of back ventilation through the make-up line, a second oil separator can be added on that side of the system between the engine and intake. I don't really see any good reasons to vent it to atmosphere, other than out of spite for the Earth.

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PostPosted: February 11, 2019, 12:29 pm 
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Driven5 wrote:
The PCV valve on a naturally aspirated engine should actually be opened to the maximum flow position at WOT

Agreed, and to expand on that here's my 2 cents for what it's worth.
The PCV valve contains an internal 'shuttle' spool (you can hear it rattle when you shake the valve back and forth). On a NAE, at idle the manifold vacuum is the highest, this high vacuum, via the PCV valve hose, draws the 'shuttle' up to close the PCV valve. If it didn't the engine would experience a vacuum leak at idle and run poorly. If you want to test this just remove the PCV valve from the valve cover at idle and take the PCV valve off the end of the PCV valve hose.
At WOT the engine vacuum is lower (and throughout the complete throttle range) allowing the PCV valve 'shuttle' to float within the PCV valve allowing crankcase vapors to be drawn into the engine intake to be introduced into the combustion chambers and be burnt. The amount of vacuum leak that's happening to do this is not noticeable at increased RPM's. Engines also had a tube going from the VC to a crankcase breather element that was situated in the air filter housing. This element would filter crankcase vapors at idle (when the PCV valve is closed) and introduce these vapors into the top of the carb to be burnt in the combustion process. At higher RPM this flow would reverse through the element as the PCV valve would start to do it's job.
It's a very simple and effective system for getting rid of crankcase vapors.
I don't want to date myself but I remember when I was a kid the pre 60's engines had a crankcase vent pipe that came out the VC (or crankcase) and dropped beside the engine to the oil pan level. The VC also had a breather cap. When the vehicle was in motion the air passing under the engine by the vent pipe would create a negative pressure in the pipe (the end of the pipe was cut at an angle for this purpose). This would draw air through the VC breather cap and whatever crankcase vapors that were present out the vent pipe into the atmosphere. Not an environmentally friendly system. I remember seeing engines idling and vapors puffing out through both the VC breather and the vent pipe if the engine has excessive blow by.
Anyhow, that's my 2 cents.

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PostPosted: February 11, 2019, 2:56 pm 
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when the evacuation pump is running, drawing a vacuum on the crankcase and less vacuum is present in the intake the PCV valve will shut much like a check valve.

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PostPosted: February 11, 2019, 4:40 pm 
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john hennessy wrote:
when the evacuation pump is running, drawing a vacuum on the crankcase and less vacuum is present in the intake the PCV valve will shut much like a check valve.


And this was the infamous 1970's "Smog pump" that darned near everyone disabled if they thought they had an engine issue?

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PostPosted: February 11, 2019, 7:44 pm 
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geek49203 wrote:
And this was the infamous 1970's "Smog pump" that darned near everyone disabled if they thought they had an engine issue?


Are you talking about the air pump that introduced atmospheric air into the exhaust stream via individual ports on each cylinder exhaust manifold outlet?
If so this was done because the exhaust gas leaving each cylinder was still burning the fuel charge. Introducing more air (20% oxygen) allowed the exhaust gas to do a more complete burn of the exhaust gas creating a cleaner exhaust emission.

And guilty as charged, I've removed my fair share of them, many from brand new vehicles at the fleet shop I worked at....... :oops: because that's what we did.

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PostPosted: February 11, 2019, 8:54 pm 
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horchoha wrote:
And guilty as charged, I've removed my fair share of them, many from brand new vehicles at the fleet shop I worked at....... :oops: because that's what we did.


Circa 1981, I lived in an apt next to a muffler shop that removed catalytic converters by the dozens, each day, replacing them with "test pipes". Cause that's what we did.

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PostPosted: February 11, 2019, 10:43 pm 
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Are you sure you don't have a ring that is flipped or a bore that glazed? How do your gaps compare to factory?

To your point you either have a large enough hole going outside of the block to allow crankcase pressure to escape and the catch can keeps the vapor from going everywhere or you run an air/oil separator and pull a vacuum from the intake. Every time I've had oil pouring out of an engine, it was either a thrown rod or worn rings. I spent several race weekends convincing myself it wasn't rings and tried all sorts of crankcase ventilation tricks. When I finally bit the bullet and ran a ball hone through the bores and tossed in a new set of rings, the problem magically vanished (ok....well diminished significantly - it was still British).

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PostPosted: February 12, 2019, 9:16 am 
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a.moore wrote:
Are you sure you don't have a ring that is flipped or a bore that glazed? How do your gaps compare to factory?


Had a GM Iron Duke in a Buick years ago, when I was REALLY broke. Thing was pushing out oil, blowby... The cylinder wall had a long slice in it. Just put it back together and kept driving it. It was using a quart of oil every 30 miles when I parked it... the oil in the crank case was always clean, like new engine's motor oil.

Also used a quart of trans fluid and a gallon of water in that 30 miles.

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PostPosted: February 12, 2019, 1:14 pm 
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i have just rebuilt the engine and i know how good or bad it is, my bores are exactly what is sized by the piston manufacturer with the correct plateau honed finish for the pistons i am using, my ring gaps are exactly as specified and all good, of course there is an element of "feel" to ring gaps but i am sure i am within .001 of the specified size.

back to the PCV valve, when the valve is sensing vacuum from the intake, you may think its closed because the "plunger" has moved to the intake end, however there is always a bypass so it is actually not closed, the reason that so many different PCV valves are available is partly due to this bypass and a variation in spring rate. the base bypass should keep the crankcase at or just below atmosphere, as the intake vacuum diminishes as the throttle opens to a point of cruising the plunger starts to drop so that it is open.

the problem here is a combination of spring rate, intake vacuum, crankcase pressure, bypass rate and volume which are all unknown at multiple throttle settings and load.

so trial and error comes into play here, if you knew the flow rate and characteristics of the different PCV valves then selection would be much easier but this seems to be a guarded secret and whether your power valve was factory or aftermarket.

one particular manufacturer of adjustable power valves has tested thousands with no consistency from like to like.

and Geek no my air pump is nothing like a smog pump that you all took of in the sixties, it is a smog pump in a way, its what is known as a supplementary air pump, its electric, if you don't know the use of a factory supplementary air pump ask any competent technician about readiness checks and supplementary air or supposedly old or slow reacting 02 sensors that you know are new.

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PostPosted: February 12, 2019, 2:06 pm 
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i have ordered a PCV valve for a turbocharged mazda 6 in case the valve i have now is off somewhat.

also the size of the make up air orifice may need adjusting or indeed deleting.

i installed a vacuum/pressure gauge on the crank case and sealed all the open places that air could enter the crankcase, and started the engine, at idle with 21hg it did not move, no vacuum and no pressure but i would like to do this test again when its mobile and under load and perhaps a different point on the engine and different PCV valves

i still have much to do on the catch can and air evacuation pump, i have to find the point where the PCV valve no longer controls the crankcase pressure, at that point i will turn on the pump, don't forget that the PCV system is for NA load levels and certainly not loads above 100% so this oil leaking thing should have been expected when the motor gets over 100% load

the effectiveness of the pump will depend on how much air is sucked in through the make up air pipe over the amount needed for the PCV at cruise and if the pump is man enough to pull the blow by and the make up air.

i have a vacuum operated valve which could be switched between adding the make up air and closing it off when the pump is needed diverting all crank case pressure to the pump

i must say that in spite of throwing oil everywhere from the front and rear main seals, that the blow by is within the limits of the PCV system at cruise, its just in high levels of load where it was never designed to work from the factory that i think i have a problem.

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PostPosted: February 12, 2019, 2:20 pm 
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I run a dry sump on my turbo Honda K24. There's enough blowby that at idle at a light, when the wind is right it looks like I have either oil leaking onto the exhaust, or maybe an electrical short... No one's yelled at me that the car's on fire but I suppose it'll happen eventually. Somewhat related, cost aside, a dry sump is the best think you can do for an engine in a hard cornering Locost, but yeah, the cost is substantial.

I had someone argue with me that the dry sump would cost more than his engine, using that reasoning to not install it. So he goes to a trackday event, using the gas to get there, pays the $$$ entry fee, get's a hotel room, and food, and blows up his engine due to oil starvation. Okay, no problem, so he installs another identical engine. What can logically be expected to happen every time he goes to a trackday event? How many ruined events does it take to pay for the dry sump, or to completely lose interest in the car?

I'll sit down now.

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PostPosted: February 13, 2019, 3:37 am 
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So you were using a naturally aspirated PCV valve/system on a forced induction engine? No wonder you are having problems with it. Now that you have a more appropriate valve, the 'correct' way to set the system up would be like this:

Attachment:
CCV20diagram.jpg
CCV20diagram.jpg [ 18.15 KiB | Viewed 301 times ]

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