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Oil catch can
- Thread starter Stephen@NCAutoUSA
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1. There should never be a filter (breather) on any PCV design, ever. Allowing the atmosphere to exchange gasses with the PCV system eliminates your PCV action!
2. The best design will minimize the crankcase pressure during boost. The lower the pressure in the crank case, the more power the engine will make as a percentage based on how badly it needs the help. Big block blown chevys use belt driven vacuum pumps for an additional 50-100 horsepower (something like 4-8% more power). Keep in mind very low pressures inside the crankcase mean that the oil seals need to be up the challenge, or you are just as likely to suck one in with low pressure as you are to blow it out with high pressure.
3. IF your engine has a turbo, and you do not want to run a dedicated vacuum pump for pcv action during boost, you have two other common options. The first was posed by DDozier on page#4 where the pcv action is contributed by the turbo inlet. The second was also mentioned by DDozier a few pages back, and includes an exhaust scavenging hardware that allows your exhaust system to pull a vacuum on the crankcase during boost.
4 . Every engine will benefit from PCV action both on and off boost, it will help keep the oil cleaner by removing the hodgepodge of combustion byproducts produced when an engine is running, it will improve economy and increase power output and engine efficiency overall.
2. The best design will minimize the crankcase pressure during boost. The lower the pressure in the crank case, the more power the engine will make as a percentage based on how badly it needs the help. Big block blown chevys use belt driven vacuum pumps for an additional 50-100 horsepower (something like 4-8% more power). Keep in mind very low pressures inside the crankcase mean that the oil seals need to be up the challenge, or you are just as likely to suck one in with low pressure as you are to blow it out with high pressure.
3. IF your engine has a turbo, and you do not want to run a dedicated vacuum pump for pcv action during boost, you have two other common options. The first was posed by DDozier on page#4 where the pcv action is contributed by the turbo inlet. The second was also mentioned by DDozier a few pages back, and includes an exhaust scavenging hardware that allows your exhaust system to pull a vacuum on the crankcase during boost.
4 . Every engine will benefit from PCV action both on and off boost, it will help keep the oil cleaner by removing the hodgepodge of combustion byproducts produced when an engine is running, it will improve economy and increase power output and engine efficiency overall.
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Here's something that I don't understand in many of the approaches above: they treat the two valve-cover ports the same, as sources from which to pull from the crankcase. But that means there is no breather tube as designed, substantially limiting the flow through the crankcase and the circulation path. This seems hugely significant to the ability of the PCV system to clean the oil. Is someone able to explain the logic to me?
I'd also like to understand why PCV systems are designed for reduced flow at idle. Is there a downside to excess flow? Maybe increased IAT, but that seems insignificant under vacuum conditions.
I'd also like to understand why PCV systems are designed for reduced flow at idle. Is there a downside to excess flow? Maybe increased IAT, but that seems insignificant under vacuum conditions.
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I'll be nice answering the first question in regard to the previous approaches: You are asking the right questions and on the right track to developing a proper system that not only hopefully provides a crankcase suction to promote ring sealing at high RPM, yet also circulates the crankcase at low RPM to help keep the oil clean. None of the systems described above do both.
As far as the second question, idle is when the flow is the greatest through the crankcase. The large vacuum behind the closed TB promotes a lot of circulation.
Thanks for the feedback. Isn't it as simple as adding a separator in the suction side of the OE system?
From what I read about PCV valves, they are open with a zero pressure differential, close against pressure driving flow toward the valve cover, and proportionally close with pressure driving flow out of the valve cover. Maybe I need to experiment with the PCV valve from an NSX. Are you saying they are simple check valves?
Yes, but to do it correctly, you need to have it on both lines to the intake. The rear valve cover during periods of high blowby (high engine RPM) may switch from suck to blow!
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Look on page 11-134 of the SM for a description how the OEM system works. Keep in mind Honda got their car front/back messed up in this diagram. The only PCV valve is on the front VC.
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good point. It does appear that two separators is best.
In the 97+ manual, it's on 11-166 and the schematic is on 11-9. And for my car, an '00, the schematic is in the supplement because they added the secondary air injection. But Honda's description in the SM is not inconsistent with the general descriptions of PCV valves as reducing flow under vacuum while stopping reverse flow.
No, PCV valves are normally closed. They are not simple check valves, but when I bought a new Honda valve and blew into it, I couldn't observe any flow regulation based on dP. I haven't measured the flow through the system, but OEM engineers perform a balancing act on the lines and valve to regulate flow at various engine loads based on expected blowby. It's a balancing act that we disturb when we modify the engine with higher cylinder pressures or wear out the rings as they age. My non-scientific test blowing through a new Honda PCV valve is what I based my statement in post #104 on. If crankcase blowby exceeds the PCV valve/hose capacity, then the other line off the other VC will provide flow as well. It switches modes from cleaning to venting. That's why you need to be clear on the two things the PCV system is designed to do.
In a FI system on a stock engine, peak cylinder pressures are higher leading to theoretically more blowby. I know the top rings on the OEM pistons have a very small gap, which leads to them closing under these severe conditions and breaking the ring lands. That's my theory anyways. I think you could take apart a stock engine and file down the rings for a larger gap and these "400WHP" limitations on the stock engine could be bumped up to 475WHP or so. But if you're going to the trouble, why not replace the OEM pistons?
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I may try to characterize the PCVV some time. I guess knowing the VC pressure (should be crankcase pressure) would be good info. I believe I read a post from about a decade ago hat said it was max of a couple psi. It seems low enough that there wouldn't be much downside to using a check valve on the breather hose instead of a second separator, so long as the crack pressure is low.
On your other point, I didn't replace my pistons because that requires sleeving the NA2, adding considerably to the expense. I didn't consider opening the ring gaps.
On your other point, I didn't replace my pistons because that requires sleeving the NA2, adding considerably to the expense. I didn't consider opening the ring gaps.
It shouldn't be more than a few psi because that would put quite a bit of structural load on the fragile magnesium VC's. That's why I thought my non-scientific method of blowing into the new Honda PCV valve was acceptable to characterize the flow.
Before you add a simple check valve into your front VC, keep in mind that the non-pcv-valved VC is the path of least resistance from crankcase to intake manifold. The PCV valve is a significant obstruction to flow. Try blowing through it. During periods of high blowby, it is your other VC line that is providing most of the crankcase pressure relief. I wouldn't personally add a check valve to it to prevent that relief flow.
Oh, my comment on pistons wasn't directed to you - just more of a general thought while we're talking about blowby. Seems like a lot of stock engines that have been FI'd have significant blowby.
Dave
Before you add a simple check valve into your front VC, keep in mind that the non-pcv-valved VC is the path of least resistance from crankcase to intake manifold. The PCV valve is a significant obstruction to flow. Try blowing through it. During periods of high blowby, it is your other VC line that is providing most of the crankcase pressure relief. I wouldn't personally add a check valve to it to prevent that relief flow.
Oh, my comment on pistons wasn't directed to you - just more of a general thought while we're talking about blowby. Seems like a lot of stock engines that have been FI'd have significant blowby.
Dave
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That's a good point Dave. Seems like two catch cans will be in order. Darn. Although you may have seen some of the so-called clean-side separators that replace the oil filler cap and allow the entering air flow but no exit oil flow. Perhaps they suffer from the same problem you raise with a check valve.
As for flow through the PCVV generally, it will have a ~10 psi driving force under vacuum.
I dont know know if any blow by oil makes it to my intake but I'm interested tonfind out. I'll bet that was the cause of all my problems after the rebuild with vacuum line 4 clogging. But now that the rings have seated perhaps it's not the same degree of an issue.
As far as the design of the can itself goes, I find the discussion in this forum post and following it quite interesting. I think that the author overstates the problem with media proximate to the exit port (in the Moroso design), and also think the issue could easily be solved with a spacer of sorts as I don't really see the exit flow reaerosolizing the oil. And I like the use of coalescing material in the maximally cooled exit flow in addition to the entrance flow.
As for flow through the PCVV generally, it will have a ~10 psi driving force under vacuum.
I dont know know if any blow by oil makes it to my intake but I'm interested tonfind out. I'll bet that was the cause of all my problems after the rebuild with vacuum line 4 clogging. But now that the rings have seated perhaps it's not the same degree of an issue.
As far as the design of the can itself goes, I find the discussion in this forum post and following it quite interesting. I think that the author overstates the problem with media proximate to the exit port (in the Moroso design), and also think the issue could easily be solved with a spacer of sorts as I don't really see the exit flow reaerosolizing the oil. And I like the use of coalescing material in the maximally cooled exit flow in addition to the entrance flow.
Jason, when searching for (2) A/O separators for my N/A setup, I saw the RX design. However, it is(was) $350+ for one, and I needed two. That's why I settled for two of the cheaper Moroso's. No, they're not perfect, but I didn't have time to design my own, and it was the next best alternative in the effectiveness/$ ratio IMO :smile:.
It's a moot point now since they are sitting in the garage collecting dust while I've changed setups. It was just another way for me to gauge how well I built my first engine.
I never had a problem with a gunked TB or oil in the intake manifold when I took apart my N/A engine with ~120k miles on it. Others have seen significant crud around the TB plate (could be due to an improperly-oiled K&N or Unifilter), and even Honcho mentioned he had pooled oil sitting at the bottom of his N/A manifold when he took it apart (N/A stock engine).
I think a proper A/O separator and functioning PCV system is even more essential on a boosted OEM engine. That's due to the increased combustion pressures and (probably) richer tunes that wash the cylinder walls and rings leading to accelerated wear. That's why richer is not always better in FI. People quote their A/F ratios on here for boosted setups and they are much too rich IMO. Oh well, I'm no tuning expert and I guess it is better for the engine to die a slow death than a quick one!
Dave
Just reread this thread.
This reply interests me though. Would you replace the filter/filter with a vacuum line or could you also add the vacuum line as well along with the filters? Ultimately the filters would just breath but a vacuum source would just be extra assurance?
You wouldn't want the vacuum line and a filter, as it would just draw air into the filter and not provide any suction from the crankcase.
Ok gotcha.
Moroso AOS not 100% effective
I tested my catch can system on track a couple of weeks ago and I'm not 100% satisfied with the result.
The setup is straightforward : the two camshaft covers are tee'd together before entering the Moroso AOS and the output goes to the turbo inlet through a bernouilli pipe after the air filter.
There is no PCV valve in the system.
In practice there is still some oil spray coming out of the BOV during track use and there is only a limited amount of fluid trapped in the Moroso AOS.
After looking into the NSX service manual, I found out that in the oem setup ( no turbo of course) fresh air is pulled in through the rear camshaft cover to exit through the front camshaft cover.
This could be replicated in my setup by connecting only the front camshaft cover to the AOS while the rear camshaft cover could be connected to another catch can vented to atmosphere through a small air filter.
In this manner the vacuum would be reduced in the crankcase thus reducing the amount of oil pulled through the AOS.
Reinstalling the PCV valve would also reduce the flow if needed but with the risk of having oil fumes coming out of the small air filter when the PCV valve remains closed...
Any thoughts or better ideas like using the exhaust as the vacuum source?
PS: I can't find the post that mentions the exhaust as the vacuum source?
I tested my catch can system on track a couple of weeks ago and I'm not 100% satisfied with the result.
The setup is straightforward : the two camshaft covers are tee'd together before entering the Moroso AOS and the output goes to the turbo inlet through a bernouilli pipe after the air filter.
There is no PCV valve in the system.
In practice there is still some oil spray coming out of the BOV during track use and there is only a limited amount of fluid trapped in the Moroso AOS.
After looking into the NSX service manual, I found out that in the oem setup ( no turbo of course) fresh air is pulled in through the rear camshaft cover to exit through the front camshaft cover.
This could be replicated in my setup by connecting only the front camshaft cover to the AOS while the rear camshaft cover could be connected to another catch can vented to atmosphere through a small air filter.
In this manner the vacuum would be reduced in the crankcase thus reducing the amount of oil pulled through the AOS.
Reinstalling the PCV valve would also reduce the flow if needed but with the risk of having oil fumes coming out of the small air filter when the PCV valve remains closed...
Any thoughts or better ideas like using the exhaust as the vacuum source?
PS: I can't find the post that mentions the exhaust as the vacuum source?
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- 13 December 2011
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SCW Performance breather tank / oil catch tank setup.
Mounts to OEM targa engine cover bracket. Utilizes a TiG welded breather box, baffled, and filters the exiting air pressure.
Has 2 -10 or -8 inlets, depending on your config. PCV delete, and a drain on the lower of the tank.
Ive been running this setup for about 2 months now with my supercharger setup, no problems to date. You can definitely feel the volume of pressure venting from the engine, I feel that the OEM setup is not very efficient especially once you go F/I.
Attachments
Ideally there are no catch cans. A catch can is to catch oil when you have no other option (you cannot fix the oil 'leak'). In other words, the engine should never spill out oil under any circumstance; if it does, there is a baffle issue, it requires a baffling modification (take the offending part off the engine and re-engineer it to baffle the oil properly). the catch can is a band-aid box that allows you to circumvent the re-engineering of the baffle. As an example, many Honda S2000 engines have oil baffle issues when taken to a track, the 're-engineering' approach is to drill several holes in the baffle plates allowing oil to drain back to the engine more easily (to keep it from getting 'trapped' in the top of the engine). This is just one example; there are many ways to 're-engineer' the baffle system.
PCV has nothing to do with catch cans. PCV HATES catch cans, or any additional plumbing volume. Exactly like an intercooler which is too large, or an exhaust which is too large, the extra space is detrimental to performance, forces the system to move more volume and this reduces the effectiveness of the pressure drop. Any extra lines/cans/plumbing is going to negatively impact the PCV action.
Now, on to the crank case. During cruise the PCV valve flows from crankcase -> intake manifold (or suction side of the engine somewhere) to feed the cylinders air from the crankcase. The air from the crankcase comes from two different places: 1 is from blowby gas, and the other is a fresh air source that leads from the crankcase -> air filter tract (from the factory this is how it routes). The idea is, as pressure drops in the crank case due to the PCV valve allowing the engine cylinder to suck air from the crank case, that pressure drop is 'relieved' by the fresh air source, plus, whatever gasses have passed the piston rings. The more blow-by gas that passes the rings, the less the PCV valve will pull on the fresh air source. The reverse is also true (if the engine had 0% blow by then 100% of the crankcase air would come from the fresh air source). This leads our discussion to the fresh air source next.
The fresh air source is the air filter tract. it is after the air filter, such that the air is clean. a very high quality air filter (like an OEM paper element) is ideal since the cleaner the air going into the crankcase the better for the engine health. This is paramount to understanding #1 that the PCV system and oil cleanliness and engine health is all tied together back at the air filter.
Next, we discuss PCV action while the pcv valve is shut. When you go into boost, or during WOT, generally the PCV valve is SHUT COMPLETELY. That means that there is only 1 way for crankcase air to go: towards the air filter tract. So when the engine goes into boost, the air is allowing to exit the crankcase (any blowby gas) and enter into the air filter tract. This is where I point out that the ability of the air filter tract to 'PULL' on the crankcase is directly related to the air filter restriction. As the air filter becomes more and more restrictive, the pressure in the inlet tract (post air filter, i.e. the compressor inlet to the turbocharger if you had one) becomes lower and lower, and pulls harder and harder on the crankcase. Likewise, if the filter is removed, or flows very well (no pressure drop) then there will be pressure drop in the air filter tract, and thus no 'pulling' on the crank case. You might wonder at this seemingly contradictory state; you are told that during WOT you need PCV action for ring seal which will help with power output, but then also told that the only way to get that pressure drop is to use a restrictive air filter which will reduce power output. Let me clarify this situation immediately. The increase in pressure drop due to a restrictive air filter is a cleaning effect, one that improves the quality of the oil, it is NOT going to improve engine output, despite the increased ring seal. The reason is simply that the more restrictive air filter will force the engine/turbo to work harder to get air, and that will decrease engine output. Thus, a proper PCV system on an OEM vehicle, using a restrictive paper OEM element, is an OIL CLEANING/ENGINE HEALTH feature only. It has nothing to do with power output increasing. It is there to maintain cleaner oil when the pcv valve is shut.
Alternatively, there is a way to get a power improvement while also keeping a very non-restrictive air filter, by using a vacuum pump apparatus (usually race cars only), or to route the pressure drop of the WOT-PCV action to an alternative driving source such as the exhaust system.
[MENTION=31132]kingtal0n[/MENTION] what about vapors in the flow when the PCV valve is flowing? It seems that a catch can is beneficial in that those vapors are undesirable for combustion.
And on the fresh-air side, I agree that generating suction with a restrictive air cleaner is undesirable, but a catch can for flow toward the intake accounts for any flow created by blowby driving the pressure differential. In other words, assume no filter (or a perfectly clean, nonrestrictive one), and WOT results in flow towards the intake because of elevated crankcase pressure created by blowby. In that case, a catch can seems helpful to remove vapors in the flow.
As to the negative effect of a catch can, placing one in the fresh-air flow would seem to have nearly no downside. And for flow from the PCV valve, I take it you prefer to avoid the increase in total volume between the valve and intake because that increase will slow the response? I.e. Create a low-pass filter at the valve for pressure variation at the intake? My guess is that typical intake pressure variation is an order of magnitude slower than the connection between the valve and intake, so I don't see that realistically affecting performance. But I could be off in that guess.
Anyhow, useful discussion, thank you.
And on the fresh-air side, I agree that generating suction with a restrictive air cleaner is undesirable, but a catch can for flow toward the intake accounts for any flow created by blowby driving the pressure differential. In other words, assume no filter (or a perfectly clean, nonrestrictive one), and WOT results in flow towards the intake because of elevated crankcase pressure created by blowby. In that case, a catch can seems helpful to remove vapors in the flow.
As to the negative effect of a catch can, placing one in the fresh-air flow would seem to have nearly no downside. And for flow from the PCV valve, I take it you prefer to avoid the increase in total volume between the valve and intake because that increase will slow the response? I.e. Create a low-pass filter at the valve for pressure variation at the intake? My guess is that typical intake pressure variation is an order of magnitude slower than the connection between the valve and intake, so I don't see that realistically affecting performance. But I could be off in that guess.
Anyhow, useful discussion, thank you.
thanks for the questions
First lets talk about vapor. How is your chemistry background? A vapor, can/should be called a gas. Gas state molecules will NOT stop in a catch can. A catch can is going to trap a liquid or solid state molecule only, and even then most of the liquids and byproducts of combustion in an engine have partial pressures which allows them to gradually send out gas state portions over time. There is not a single OEM manufacturer that I know of which uses a "can" between the intake and pcv valve to catch "vapors" since as we discussed, a catch-can won't do you any good for those. If you had a problem with liquid oil spilling past the pcv valve (baffle problem) then a can might be beneficial as a band-aid (temporary solution) while you fix the real problem: oil baffle.
If you go to WOT, and have a perfect air filter, then the situation you describe is highly undesirable because it means that the pressure in the crankcase has risen above atmospheric pressure somewhat. In other words, in order for the blow by gasses to push air from the crank case, into the air filter tract, the pressure in the crankcase must be higher than the atmospheric pressure (which is what is in the air filter tract, since the air filter is 'missing'). That means you have NO pcv action during WOT, and while this is better for making power/performance, it also means that every oil seal in the engine is experiencing a slight 'push' and this will gradually push oil from those oil seals, it will begin to show up at every oil seal in the engine, a small trickle at first but eventually contributing to leaks everywhere oil can find a way out. That is why the slightly restrictive filter causing PCV action is a CLEANING benefit to the engine: it allows the crankcase to be pulled below atmospheric pressure during WOT so that oil is not pushing into the seals of the engine, causing leaks over time.
A smallish catch-can on the fresh air side is somewhat negligible with respect to flow, since the pressure differential in this tract is often very very tiny (often 3-15" of H2O) and many will install one here to protect their turbocharger's compressor from the liquid oil which can be pulled or pushed from the crankcase. The OEM manufacturers provide a 'better solution' and include 'convolutions' in their intake plumbing to help trap the liquid 'sludge' product which builds up there over time, in factory equipped turbo vehicles. There is often also a restrictor on this side to help the crankcase build a negative pressure (below atmospheric) during normal vacuum PCV valve action driving. The response of the fresh-air tract is negligible with respect to performance, this is purely a method for trying to clean the engine, and if you add a bunch of plumbing volume to this side you are only slowing down the ability of the air filter tract to pull from the crankcase to some extent, which we already realized will facilitate oil leaks. So you can think of any plumbing volume added to the crankcase in general as a way to increase the potential for oil leaks everywhere, and/or diminishing PCV action.
Preferably, you would have a pcv system which uses the exhaust as a way to pull from the crankcase. This will bypass the combustion chamber and route directly into the exhaust (normally it would move from crankcase -> intake -> chambers -> exhaust) So you are bypassing the intake->chambers portion of the chain of command, it still winds up in the exhaust system anyways either way. With the exhaust driven system, whatever the pcv system pulls from the crankcase is no longer being burnt, is no longer being allowed to coat the inside of the intake manifold/valves/combustion chamber with oil/combustion byproducts pulled from the crankcase. Although these exhaust driven systems can be difficult to setup and require (so I am told) a very free flowing exhaust system to work correctly (I have not done much of my own testing besides one engine perhaps 10-12 years ago, with good success I might add)
I might have posted this alrdy a year ago but fwiw here it is again. This is the OEM setup for an Originally turbo vehicle, such as sr20det. "A" is the traditional way to route PCV to the intake. If we move the tube to "B" we are bypassing the combustion chambers and routed into the exhaust directly.
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I was contemplating using the exhaust as the vacuum source but...my local mechanic advised me against it.thanks for the questions
Preferably, you would have a pcv system which uses the exhaust as a way to pull from the crankcase. This will bypass the combustion chamber and route directly into the exhaust (normally it would move from crankcase -> intake -> chambers -> exhaust) So you are bypassing the intake->chambers portion of the chain of command, it still winds up in the exhaust system anyways either way. With the exhaust driven system, whatever the pcv system pulls from the crankcase is no longer being burnt, is no longer being allowed to coat the inside of the intake manifold/valves/combustion chamber with oil/combustion byproducts pulled from the crankcase. Although these exhaust driven systems can be difficult to setup and require (so I am told) a very free flowing exhaust system to work correctly (I have not done much of my own testing besides one engine perhaps 10-12 years ago, with good success I might add)
I might have posted this alrdy a year ago but fwiw here it is again. This is the OEM setup for an Originally turbo vehicle, such as sr20det. "A" is the traditional way to route PCV to the intake. If we move the tube to "B" we are bypassing the combustion chambers and routed into the exhaust directly.
The reason beeing that in case of an engine malfunction ( broken piston as an example) a large quantity of oil would go straight into the exhaust and catch fire immediately.
In no time at all the whole car goes into flames with no chance of extinguishing the fire...
Vapors condense when they cool. A catch can or AOS filled with high-surface-area material like metal wool provides a lot of opportunity for condensation. That and the slowed velocity resulting from the larger flow area are what I understand the benefit to be of an AOS. Moreover, it seems reasonable to expect some aerosolized oil droplets in the flow, which will also be collected if they impinge on a surface or if the flow drops below a certain velocity.
Perhaps you are distinguishing a catch can from air-oil separators? I don't find it useful to talk about a catch can as an empty vessel with ports in it. Why someone would use that is beyond me. I am interested in devices designed to condense vapors and remove droplets from the flow. OEMs do use such devices, such as the vortex-based collector that BMW has used.
Unless atmospheric pressure is somehow driving flow, I don't see why it's particularly relevant that the low-pressure end of a flow path is slightly below atmospheric. Here, the high-pressure end is driven by internal engine conditions. I'd have to know what pressures we are talking about in order to have any idea of the magnitude of the effect.
General statements like this are rarely all that useful unless you provide some reason or evidence that the effect is significant. Increased volume may affect the transient response but as I have pointed out, it seems unlikely that it would have a meaningful effect.
That does not sound right. If a large quantity of oil goes into the exhaust system of a broken engine, the engine is no longer making power (it broke) and the temperature will rapidly be cooled by the sudden addition of liquid oil. Furthermore the exhaust system is well contained, and fire/flames have a habit of forming there regardless of whether the engine is broken or not. That is kind of it's job.
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A 'vapor' is a gas state molecule, which liquid oil is never. You do not vaporize engine oil easily, it is not like gasoline. If you heat a vat of liquid oil to 212*F what is it's partial pressure? That is the answer you are looking for. It can be whipped into a flurry of miniature oil droplets, but these are still fine droplets of liquid state molecules which collect on any object, it doesn't matter if you use a can, or a looooong tube, the oil 'vapors' are going to collect on anything they can if given an opportunity, it does not need to cool or slow down but will gradually collect as a film of 'sludge' no matter what the temperature is. If you do not control the oil with the baffle of the engine, then of course it will collect in whatever comes next, be it the intake manifold or valves or some kind of tube or can.
General statements are all we have. Even if you test a particular engine and gather real world data, there is no guarantee the next exact same engine will perform identical because often engines are experiencing different conditions as they age and acquire mileage. What we are trying to do instead is create a model: Use very basic, easy to understand comparisons which set some variable as a constant (if we call a constant atmospheric pressure for example, 15psi to make it simple) then we can safely say that 15.X+ is above and 14.9X- is below and work within those boundaries for our model for example.
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A 'vapor' is a gas state molecule, which liquid oil is never. You do not vaporize engine oil easily, it is not like gasoline. If you heat a vat of liquid oil to 212*F what is it's partial pressure? That is the answer you are looking for. It can be whipped into a flurry of miniature oil droplets, but these are still fine droplets of liquid state molecules which collect on any object, it doesn't matter if you use a can, or a looooong tube, the oil 'vapors' are going to collect on anything they can if given an opportunity, it does not need to cool or slow down but will gradually collect as a film of 'sludge' no matter what the temperature is. If you do not control the oil with the baffle of the engine, then of course it will collect in whatever comes next, be it the intake manifold or valves or some kind of tube or can.
these are devices integrated to the oil baffle capability of the engine. The term "oil separator" is synonymous with "oil baffle" and has nothing to do with catch cans. If an engine has an external baffle then the original designers realized the necessity for one (they 're-engineered' their engine's internal baffle and new, updated design happens to be external to the crank case) It helps keep the airflow free from oil droplets/vapors or whatever you want to call them. I am not sure what the partial pressure of engine oil is at 212*F but I am somewhat confident that it is negligible with respect to the quantity that is able to pass a given random OEM baffle in a liquid state (even if finely 'micronized' or whipped up into tiny droplets). In other words, if there is some partial pressure action involved, then it will be there regardless of whether the oil is sitting in the crankcase or in a 'catch-can' type device, and headed towards the intake manifold. The warm oil is going to have gas state molecules leaving per unit time and there is no way to prevent any true gaseous product from eventually making its way in... or out of a 'can' intended to collect the oil vapor as a liquid product. If you remove the plumbing from a high mileage PCV tract you will find perhaps a large quantity of liquid oil or 'sludge' type of product which collected in the tube on it's way to the intake manifold due to similar circumstances to what I just described. If you remove the tube and replace it will a 'can' it will perform the same function, there was never any reason or need to use a larger volume unless the actual volume of liquid oil passing the crankcase is somehow increased (due to additional blowby or a failing baffle pushed beyond its OEM performance expectations i.e. due to increased redline or boost)
It is a simple fact that if the pressure of the crankcase goes higher than atmospheric pressure, it will push on the oil seals of the engine and help facilitate oil leaks. You do not want this condition to exist, ever; therefore it is important to create a pressure drop (below atmospheric) in the crankcase whether at WOT or IDLE or cruise. The idle/cruise is done by the pcv valve action. The WOT pressure is driven down by the slightly restrictive air filter.
I agree above that "it will not have a meaningful affect" =
This space does not care about "transient response" except with respect to the engine oil seals experience of pressure (changing pressure on either side of the oil seals is where the 'transient response' is having an affect, and is negligible overall)kingtal0n said:
General statements are all we have. Even if you test a particular engine and gather real world data, there is no guarantee the next exact same engine will perform identical because often engines are experiencing different conditions as they age and acquire mileage. What we are trying to do instead is create a model: Use very basic, easy to understand comparisons which set some variable as a constant (if we call a constant atmospheric pressure for example, 15psi to make it simple) then we can safely say that 15.X+ is above and 14.9X- is below and work within those boundaries for our model for example.
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Jason is correct. Look at the OEM rubber PCV lines. They are even insulated to ensure the bad stuff stays in solution as it travels from the valve covers back to the intake manifold. I doubt it makes a huge difference, but I kept my new rubber hoses insulated as well, and tried to place the catch cans in strategically cooler engine bay areas. That theoretically ensures any condensables remain suspended as a hot vapor until they can condense on the relatively cooler air/oil separator media.
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I agree with KingTalon. Metal exhaust piping works great as a fire barrier. A hot oil fire would take a long time to melt through it (unless you are using aluminum), and at that time, your fuel (oil) supply is long gone.
You only need to worry about placing your venturi tube at a low-pressure point in your exhaust (as close to the tailpipe as possible) but in a cross-sectional area that is small (for a higher local velocity), and somewhere after the catalytic convertors (don't want to dump crap in those unnecessarily).
However, you appear to track your car often (good for you). I would highly advise you to install one of those new Halon replacement systems, or the aqueous foam fire suppression systems with permanent nozzles. It's a good idea in general, along with practicing how long it takes you to get out of the car in the event of an emergency.
Imagine you connect one end of a tube to the crank case, and the other end is on the intake manifold.
Use different length tubes;
1"
1'
10'
100'
100000'
Now compare what you find inside the tubes of different length.
The 1" tube will be coated, perhaps even clogged with oil from a particular engine. A next engine you test, with a really good baffle, might collect only a slight residue. It is here we must realize that the tube, or 'collecting duct' as it will now be called, needs to be tailored to the needs of the engine. Engines with better baffles can use shorter, smaller diameter collecting duct tubes.
Next, look in the 1' and 10' tubes. The 1' tube may also be coated with sludge most of its length; however, the 10' tube may only have about 3-4' of collected sludge along its length, because the amount of time the engine spends running is having an influence on the ability of the sludge to move along its length. If you run the 10' tube for a year or ten years eventually its entire length may become coated with sludge type product. It is now we must realize that the collecting duct must be cleaned at some point, to prevent the sludge products from working their way fully along its length, since no liquid engine oil baffle is apparently perfect.
next look into the 100' and 100000' tubes. It is unlikely you will find very much oil or sludge deposits on the long ends of that tube. Notice our tube is not an "AOS" nor does it contain any "collection materials" it is simply a long, very very long tube which can perform the same exact function as any other 'can' or 'deposition device'. In other words, there is no way any tube, can, wood, or other material is going to stop any of the true gas molecules from passing along even the 100000' tube, because the gas never collects on the tube walls. On the other hand, liquid oil, or "collecting oil" can be found in ALL of the tubes, along their length, to some extent. If you draw a picture of the 100' tube what do you think it would look like at both ends? One end will be full of collected, liquid/solid carbon combustion byproduct sludge, and the other end is so far that it will have nothing at all, or barely anything. The problem with using such a large tube or volume is that the vacuum signal provided is diminished greatly; it is therefore important that our 'collecting duct' be tailored in such a way that A: nothing appears at its far end and that B: it is short/small enough volume that a significant portion of the vacuum signal generated in the intake manifold can be 'felt' at the crank case.
It is true that hotter sludge/oil is thinner and more likely to move easily along the length of a tube; it is important to realize that this sludge is not destined for the combustion chamber, and instead, will collect in the tube itself over time, and in whatever you install next (a can?) to try and keep it from reaching the combustion chamber. Any of this product that reaches the combustion chamber is an undesired result. That means any insulation (temperature retaining insulating material) is there only to facilitate the sludge/combustion products to move along the length of the tube and not stop, and collect there. That is ideal if you actually have a place to collect such sludge; if such a place does not exist, then any insulating material is facilitating the entry of that sludge into the intake manifold, which is undesirable. The OEM plumbing on the air filter side of the sr20det contains convolutions in the air filter tract to help collect liquid/solid product, and no such insulation, and therefore the entire length of the tube coming off the crankcase and it's pre-turbo portion of convolutions gradually gets gummed up with sludge and needs to be cleaned before it reaches the compressor inlet. You can think of the tube itself as a kind of 'catch can' since it perform this exact function, without the actual can getting in way or slowing things down. On the intake manifold/pcv valve side of the sr20det engine, there is only a very short, tiny small tube (approx 3" of tube) connecting the crankcase to the intake manifold. This is possible because the OEM baffle in the valvecover of the sr20det is very, very good at stopping liquid oil (it contains a high quality air/oil separator) and so no intervention is required (The baffle is fine). If any product did collect or form there over time, then we would intervene with some kind of additional baffle or can type device as necessary.
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