FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: drdano on July 15, 2012, 11:53:47 AM
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Hello gurus. Is there a part number floating around out there for a PCV valve that works better with engines that make low idle vacuum. Google searches say a Fram FV181 (supposedly number for a Boss 302 motor) works better at low rpm. I have 244@50 .663" lift cam in my 428 and the best vacuum I can get so far is 10" at idle with 750 DP carb. When I pull the pcv and block it with my finger, the idles drop 200+ rpm, which makes me wonder if the pcv is opening fully at idle (due to low vacuum) and shouldn't be. Anyone been down this path before have some advice on a better PCV number to try? Thanks all.
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This isn't really answering the question, but my preference would be to ditch the PCV. Any oil mist entering the intake will make the engine more prone to detonation anyway. If you want to keep the scavenging effect to go a crankcase evacuation setup where the valves are located in the collectors. This will aid in horsepower production and also eliminate the possibility of oil mist in the intake tract.
JMO - Jay
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Yeah, crankcase evac works well but you need to use straight through low restriction mufflers. Didn't work with reverse flow mufflers even the large bodied 3" Dynomax turbos.
If you want to keep the PCV, make sure you limit the mechanical advance in the distributor so you can run a lot of initial advance and also run a bit higher idle RPM to try and get higher engine vacuum. The crankcase evac is the way to go though.
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I am going to throw out a different opinion
Just off idle, part throttle, you'll have plenty of vacuum
WOT, regardless of the cam, the PCV isn't doing anything
So the last situation is idle, you arent building much crankcase pressure, so why even worry about it, just make sure its a large enough line to pull some negative pressure and take away the moisture not pressurize anything
The trick though if you want a little more at WOT, run the other breather back to the air cleaner, like a new car. That way when vacuum goes to zero, some venturi action from the air rushing into the carb will pull on the other side.
Like Jay said, you run the risk of some oil contamination, but you could also run a break box, sort of a drainable plenum if you are pushing oil, like the diesels do.
I haven't had any issues, or noticed any difference with any PCV. I see the topic come up now and again, but have always just grabbed a 3/8 90 degree for all mine, and even when I swapped PCV as this topic came up, I could never tell the difference
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Lots of different answers here, thanks for the comments. When the engine is warmed up, there is a lot of PCV fumes at idle. If I disconnect the hose it pours out of the 3/8" line pretty heavily, out the dipstick and out the opposing breather side as well. This is a new motor that isn't broken in yet, so maybe it will be better once it has?
So, if I pipe direct to my header collector, I assume I'd need to do this on both sides? With an RPM intake, where would the fresh air enter the motor if both breathers go to the exhaust? Or, would I run an open breather on one side and the opposing side to the collector? How is my 02 sensor for my AFR computer going to react to this?
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Well, generally leak down numbers are pretty good right off the bat. If you are pressurizing the crankcase now its not really a good sign.
Was it a re-ring or a new bore?
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New everything. +30 overbore to clean up the cylinders, new forged TRW pistons, new rings, etc. So, there shouldn't be hardly any PCV fumes at idle?
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There shouldn't be much coming out of there
Sometimes after sitting for a while, humid conditions, it may steam as it burns off any moisture, but you shouldn't have any significant volume/pressure being pushed out.
Any way you could make a movie of it?
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Well crap. :(
I can shoot a movie in the next day or two. There is no vapor on startup, but after 5 minutes if you pull the PCV from the breather, it pours out the breathers and some comes out the dipstick tube at idle. Likely culprit is the rings/bore not right?
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I think I'd rather wait to decide until we can see the movie, but if there is pressure pushing it out, then the rings arent sealing, bore/rings/assembly issue, could be a number of things.
Have you changed the oil since the build? If it runs decent, maybe an oil change and a good run to load the motor would burn anything off
What's the history of the build, any issues like getting very hot early on or any assembly problems?
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Should not be too much coming out of the breathers after break in - but there will be some. Not many engines are 100% sealed up. Probably close to none. If you want to reduce the airflow through the PCV just insert a slug of aluminum in the vacuum line with a .060 or so restriction hole drilled through it.
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Dano, don't know if it'll help or not but this is what I did for my PCV. When I first got mine running using the in manifold position for the PCV (little basket of steel wool and all) valve I would get a good bit of oil in the intake. So I went looking for a way to get good crankcase evac without a vacuum pump and without dumping oil into my intake. The answer for me has been an air/oil separator from Moroso. Since using this setup I haven't had any oil in the intake (or on the valve covers) and I only get about an oz of oil out of the drain after a hard day at the track or a few weeks of street driving. This is how I did it.
(http://www.clubcobra.com/photopost/data/500/IMG_1881.JPG)
(http://www.clubcobra.com/photopost/data/500/IMG_1879.JPG)
(http://www.clubcobra.com/photopost/data/500/IMG_1880.JPG)
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That is a great idea using an oil separator, which would keep the returning air in the intake clean of oil mist = less detonation. Who's PCV valve are you using underneath the separator can? I've got a Fram FV181 coming from RockAuto (couldn't find one locally), should be here wednesday and I can try it out. Rummaging around in my binds of FE spares, I did locate my original '62 Galaxie Z-code metal PCV valve, which may be of some help. You can pull it apart and clean it, but even better, the internal spring looks fairly common. I could probably find a lighter spring at the hardware store or online and be able to match it to the idle vacuum. The bypass hole looks to be around 1/8" in diameter.
Doing some reading last night, I think my initial timing may be causing some of the PCV fumes as more timing = more fumes from what I read. That's one of the reasons from the factory the timing is set so low, like around 6. I'm currently at 18 initial to try to get a better vacuum signal for carb tuning. With on-start timing retard of the Duraspark my starter isn't getting killed to bad yet, but when I shut the motor down I get a slight kick backwards on it's last 1/8 of a turn before it comes fully to a stop, so maybe I'm a tad to advanced.
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Pretty simple to hook up a crankcase evac system and they are pretty cheap. Just need to weld a tube on each exhaust pipe or header collector. The location doesn't seem to be critical.
(http://i151.photobucket.com/albums/s156/oldafretired/IMG_1034.jpg)
Then run a 5/8" hose from the check valve on the welded tube to the breather on each valve cover. Works at WOT unlike a PCV valve that would be closed. Works fine even at idle with straight though mufflers.
(http://i151.photobucket.com/albums/s156/oldafretired/IMG_1035.jpg)
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What are you using to allow fresh air into the system? My exhaust is 2.5" to 3" xpipe to 2.5x24" open steel pack mufflers, so pretty free flowing. If I put the evac connections downstream of my O2 sensor bung, would I have to worry about any oil traveling upstream to it via reversion?
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The system is sealed to try and get a bit of vacuum in the crankcase which is a good thing. Don't know for sure about oil getting on the sensor but it's hard to imagine that happening if it's upstream of the evac tube.
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Volvo used a similar system for the air injection
in the exhaust ports instead of using an airpump
A tube to each exhaust port routed to one single
checkvalve.It creates quite good vacum
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Looking at the picture "linked" and put in below. The Moroso Separator appears to be void of even the most elementry characteristics of a proper separator. Little or no centrifugal action, no baffles, improper path/materials/pore sizes for a coalescence to occur and limited void or calm plenum space for separation/storage of the captured fluid.
It looks like a simple wall divides the In/Out flow, forcing it down and back up in a "U" path over a very small reservoir. Flowing the mist/air through centrifugal action and specific stepped pore sizes encourages the fine droplets to bind together and coalesce to be captured. Realistically a typical compressed in line air filter housing would be a far better vessel to start on this job.
http://www.moroso.com/catalog/categorydisplay.asp?catcode=18549
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Valid points from our resident filtration expert! Compressor oil/air separators are super easy to come by locally and should flow more than enough air to keep up. What should you look for when selecting one?
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Do a little homework and get that tubing or line to be in a position to develop a vacuum. You want to have the flowing exhaust stream going around the tube so that it has a venturi effect on the end of the tube. It would be a good idea to rev the motor and see what you develop on the end of the hose before it's even connected to the breathers.
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The Moroso Separator appears to be void of even the most elementry characteristics of a proper separator. Little or no centrifugal action, no baffles, improper path/materials/pore sizes for a coalescence to occur and limited void or calm plenum space for separation/storage of the captured fluid.
It looks like a simple wall divides the In/Out flow, forcing it down and back up in a "U" path over a very small reservoir. Flowing the mist/air through centrifugal action and specific stepped pore sizes encourages the fine droplets to bind together and coalesce to be captured. Realistically a typical compressed in line air filter housing would be a far better vessel to start on this job.
All I can say is that it works and works well. There are others in use mostly by the import crowd which would fit your definition better. Don't forget there is a big difference between separating air and oil vs. air and water as well.
As far as the compressed air filter goes, most are plastic which I doubt would do well for long in a high heat environment, plus it would look smashing in most engine compartments.
;D
Steve
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No doubt it works but as I mentioned it's missing the basic concepts of separation which incidentally are almost universal in separating Oil/Water, Water from compressed air, Oil from compressed air, water from oil, water from jet fuel/turbine oil, diesel oil etc etc. I'm just saying if oil mist in a car motor can cause detonation then that crude separator is not capable of separating oil droplets from a gas stream with any efficiency and may likely in fact make shot gun blasts of oil droplets at times.
BTW those clear plastic bowls are typically Polycarbonate - known for being........ shall I say bullitproof? . I agree the Ind Filters are kind of ugly but then again the Mfgs make them out of SS, polished alum etc but they all have hefty pressure ratings that add weight. It's the principles of separation/coalescing that should be heeded.
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What are you using to allow fresh air into the system? My exhaust is 2.5" to 3" xpipe to 2.5x24" open steel pack mufflers, so pretty free flowing. If I put the evac connections downstream of my O2 sensor bung, would I have to worry about any oil traveling upstream to it via reversion?
Got pulled here from the new thread same topic: http://fepower.net/simplemachinesforum/index.php?topic=687.0 (http://fepower.net/simplemachinesforum/index.php?topic=687.0) and I'm not quite understanding the response to the above question.
The system is sealed to try and get a bit of vacuum in the crankcase which is a good thing. Don't know for sure about oil getting on the sensor but it's hard to imagine that happening if it's upstream of the evac tube.
Correct me if I am wrong here. But a slight vac yes... but if there is no fresh air breather somewhere (usually on a valve cover no?) isn't the vacuum created going to be pulling air through your seals?
:-\
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because the engine blow-by is what gets pulled into the header collector not fresh air , it never was about fresh air .... I've been running one of those e-vac sets like afrets picts since mid late 90's and no problems , you do occaisonlly have to replace the check valves .... I run my evac with 3 inch pipes with Flowmaster 70 series mufflers (probably the most restrictive flowmaster made) with no problems
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because the engine blow-by is what gets pulled into the header collector not fresh air , it never was about fresh air .... I've been running one of those e-vac sets like afrets picts since mid late 90's and no problems , you do occaisonlly have to replace the check valves .... I run my evac with 3 inch pipes with Flowmaster 70 series mufflers (probably the most restrictive flowmaster made) with no problems
I might not be stating the question correctly so please bear with me here. I understand it's not about fresh air. But without a breather on the valve cover to actually get the air moving through the case... it's gotta be sucking fresh air from somewhere. If the block was entirely air tight it'd be like putting the nozzle from your shop vac on the palm of your hand... no draw. The only other place I can imagine it's pulling air from to get flow is past the seals.
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the pan evac check valve in the header collector will supply the vaccum to pull it out
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the pan evac check valve in the header collector will supply the vaccum to pull it out
I get that the vaccum is created by the exhaust gasses passing past the front of the check valve orifice on the header collector. My question is where does the flow originate? Ever apply a vaccum to a bell jar for an experiment? Once the air is evacuated from the chamber to the point of the strength of your vaccum source/pump, nothing moves. You cannot pull anything out without flow though the crank case. Where is the flow coming from? Minus a breather on top of one of the valve covers I'd guess past the front or rear main.
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Blow-by is part of the origin air that e philpott is talking about. That air is coming in through the intake with the fuel mix into the cylinder. When the big-bang occurs, part of it squeezes past the piston rings and into the crankcase. The distributor hole would be another entry point, which may not be a bad thing to keep oil from weeping up past it.
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Blow-by is part of the origin air that e philpott is talking about. That air is coming in through the intake with the fuel mix into the cylinder. When the big-bang occurs, part of it squeezes past the piston rings and into the crankcase. The distributor hole would be another entry point, which may not be a bad thing to keep oil from weeping up past it.
Right. But I cannot imagine blow by allows for that much movement considering the volume of air in the crank case. Surely not enough to evacuate the suspended blow by. I do believe the vaccum provided by collector venturi would be more than sufficient to evacuate the chamber as the amount of vaccum rises and falls with the engine rpm. But it's gotta be pulling air from somewhere or IMHO there simply would not be enough flow from the case to keep it from filling. Or... I could be dead wrong. Which is why I'm asking. ;D
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the pan evac check valve in the header collector will supply the vaccum to pull it out
I get that the vaccum is created by the exhaust gasses passing past the front of the check valve orifice on the header collector. My question is where does the flow originate? Ever apply a vaccum to a bell jar for an experiment? Once the air is evacuated from the chamber to the point of the strength of your vaccum source/pump, nothing moves. You cannot pull anything out without flow though the crank case. Where is the flow coming from? Minus a breather on top of one of the valve covers I'd guess past the front or rear main.
Unless there is considerable blowby, there should be very little flow, even at greater depression. It would be prudent to use a limiter to keep crankcase pressure from getting excessively low and causing oil starvation or seal integrity issues. Now I'm curious to know how much vacuum can be seen at the port... and how to calculate proper orifice size.
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the pan evac check valve in the header collector will supply the vaccum to pull it out
I get that the vaccum is created by the exhaust gasses passing past the front of the check valve orifice on the header collector. My question is where does the flow originate? Ever apply a vaccum to a bell jar for an experiment? Once the air is evacuated from the chamber to the point of the strength of your vaccum source/pump, nothing moves. You cannot pull anything out without flow though the crank case. Where is the flow coming from? Minus a breather on top of one of the valve covers I'd guess past the front or rear main.
Unless there is considerable blowby, there should be very little flow, even at higher depression. It would be prudent to use a limiter to keep crankcase pressure from getting excessively low and causing oil starvation or seal integrity issues. Now I'm curious to know how much vacuum can be seen at the port...
I'd think adding a breather to one of the valve covers would eliminate any issues. It would let the vac to flow freely to the collector with a nominal vaccum accumulation. The only reason I asked was the picture afret posted earlier in this thread:
(http://i151.photobucket.com/albums/s156/oldafretired/IMG_1035.jpg)
showed vaccum applied to both valve covers. I like this concept as opposed to a traditional PVC setup where the blowby and suspended oil particles get recycled back through your carb or intake possibly making a bit of a mess in the process.
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no breather vent because the breather hoses go down to a one-way check vavle into the header collector , exhaust gasses passing bye the check valve creates vaccum to pullout crank case pressure , vaccum is good here (not engine vaccum).... there is NOTHING getting recycled through the carb ......
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no breather vent because the breather hoses go down to a one-way check vavle into the header collector , exhaust gasses passing bye the check valve creates vaccum to pullout crank case pressure , vaccum is good here (not engine vaccum).... there is NOTHING getting recycled through the carb ......
Exactly why I like the setup. I just questioned where the flow on his particular setup comes from with vaccum applied to both valve covers.
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HeY E : you like it setup like that ? I might do that also ...
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Adding a breather will just defeat the purpose of the crankcase evacuation system. I would say that if you added a breather, you'd get far more airflow through the crankcase evac system, and it would probably pull a whole bunch of engine oil with it. Plus you'd have essentially zero vacuum in the crankcase. Best thing to do is to seal up the engine if you are going to run any kind of crankcase vacuum.
FWIW I've run both the Moroso system and also a normal vacuum pump. Both will suck some oil out of the engine, but the vacuum pump is far worse because it creates a higher level of vacuum in the crankcase. The most I ever saw with my Moroso setup was around 5 inches of vacuum. I usually run 12-15 inches of vacuum with the pump. My preference is to use the pump, but run it only at the track, taking the belt off and adding a breather to the crankcase when running on the street. I've run the Moroso setup permanently on the street, but the engine did use some oil.
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HeY E : you like it setup like that ? I might do that also ...
I like it
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Adding a breather will just defeat the purpose of the crankcase evacuation system. I would say that if you added a breather, you'd get far more airflow through the crankcase evac system, and it would probably pull a whole bunch of engine oil with it. Plus you'd have essentially zero vacuum in the crankcase. Best thing to do is to seal up the engine if you are going to run any kind of crankcase vacuum.
. . .
Forgive my inexperience.. but isn't good flow through the crankcase exactly what you want to remove the blowby? You don't necessarily need a lot of bars of vaccum to get the suspended particulates moving... good flow volume would do that even at very low vaccum right? Unless more bars of crankcase vaccum is necessary for something I'm unaware of. And if you don't mind me asking, how do you figure such a setup with a valve cover breather might pull more oil out of the engine than a traditional setup that relies on a pump or intake vaccum? Please bear in mind I'm not asking to question anyone's judgement.. I'm asking these questions so that I can get a better understanding. You know how it is.. little bit of knowledge can be very dangerous. I'm trying to avoid being that guy. ;)
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Adding a breather will just defeat the purpose of the crankcase evacuation system. I would say that if you added a breather, you'd get far more airflow through the crankcase evac system, and it would probably pull a whole bunch of engine oil with it. Plus you'd have essentially zero vacuum in the crankcase. Best thing to do is to seal up the engine if you are going to run any kind of crankcase vacuum.
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Forgive my inexperience.. but isn't good flow through the crankcase exactly what you want to remove the blowby? You don't necessarily need a lot of bars of vaccum to get the suspended particulates moving... good flow volume would do that even at very low vaccum right? Unless more bars of crankcase vaccum is necessary for something I'm unaware of. And if you don't mind me asking, how do you figure such a setup with a valve cover breather might pull more oil out of the engine than a traditional setup that relies on a pump or intake vaccum? Please bear in mind I'm not asking to question anyone's judgement.. I'm asking these questions so that I can get a better understanding. You know how it is.. little bit of knowledge can be very dangerous. I'm trying to avoid being that guy. ;)
Better to reduce the source of the blowby than deal with the blowby. Increasing crankcase vacuum improves ring seal, to a point, by increasing the pressure differential above and below the rings. Improved ring seal=less blowby, thus less blowby to remove from the engine. Also, as crankcase pressure decreases, air mass is lowered, which should reduce pumping losses, though I've never seen this measured independently.
If the flow of blowby gases is slowed, then it should also carry less oil out of the engine, perhaps also slower moving mist particles will fall out of suspension. If you move more air, more oil mist comes with it, depending on the rate of mist generation inside the engine.
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I'm a proponent of a PCV system. I also live in a shall I say a cold moist environment at sea level and have seen the gooey mess in rocker covers.
If you your not putting a suck on the rocker cover then you will have a gooey mess. Just my experience.
"If I disconnect the hose it pours out of the 3/8" line pretty heavily, out the dipstick and out the opposing breather side as well. This is a new motor that isn't broken in yet, so maybe it will be better once it has?"
The vapour "pouring" out of the holes would be bothering me more than which PCV gizzmo to use.
It will seat in some, but I would be getting out the air line and leak gauge to see what's up.
Nothing good comes from anything pouring out of an engine.
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Adding a breather will just defeat the purpose of the crankcase evacuation system. I would say that if you added a breather, you'd get far more airflow through the crankcase evac system, and it would probably pull a whole bunch of engine oil with it. Plus you'd have essentially zero vacuum in the crankcase. Best thing to do is to seal up the engine if you are going to run any kind of crankcase vacuum.
. . .
Forgive my inexperience.. but isn't good flow through the crankcase exactly what you want to remove the blowby? You don't necessarily need a lot of bars of vaccum to get the suspended particulates moving... good flow volume would do that even at very low vaccum right? Unless more bars of crankcase vaccum is necessary for something I'm unaware of. And if you don't mind me asking, how do you figure such a setup with a valve cover breather might pull more oil out of the engine than a traditional setup that relies on a pump or intake vaccum? Please bear in mind I'm not asking to question anyone's judgement.. I'm asking these questions so that I can get a better understanding. You know how it is.. little bit of knowledge can be very dangerous. I'm trying to avoid being that guy. ;)
Better to reduce the source of the blowby than deal with the blowby. Increasing crankcase vacuum improves ring seal, to a point, by increasing the pressure differential above and below the rings. Improved ring seal=less blowby, thus less blowby to remove from the engine. Also, as crankcase pressure decreases, air mass is lowered, which should reduce pumping losses, though I've never seen this measured independently.
If the flow of blowby gases is slowed, then it should also carry less oil out of the engine, perhaps also slower moving mist particles will fall out of suspension. If you move more air, more oil mist comes with it, depending on the rate of mist generation inside the engine.
I absolutely agree it's better to deal with the source of the blowby if you are getting abnormally large amounts like the OP in the other thread.
If you don't mind me treading on your patience a little further.. ;D I'm not quite understanding how an increased vaccum on the back side of the rings help prevent blow by? I would think that you would want the bare minimal amount of vaccum in the case so it's not actually drawing vapor past the rings with an assist from the compression stroke? I'd think you'd want just enough vaccum so there is no positive pressure pushing oil past seals. And if you are drawing the vapor from the valve cover wouldn't' most of the larger particulates of oil not make it that far up into the head? Sorry for the 1000+1 questions. But I've seen a lot of cars with PVC systems that make a pretty decent mess where they dump back into the intake and I'm just trying to get my head around what works best.
-scott
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I absolutely agree it's better to deal with the source of the blowby if you are getting abnormally large amounts like the OP in the other thread.
If you don't mind me treading on your patience a little further.. ;D I'm not quite understanding how an increased vaccum on the back side of the rings help prevent blow by? I would think that you would want the bare minimal amount of vaccum in the case so it's not actually drawing vapor past the rings with an assist from the compression stroke? I'd think you'd want just enough vaccum so there is no positive pressure pushing oil past seals. And if you are drawing the vapor from the valve cover wouldn't' most of the larger particulates of oil not make it that far up into the head? Sorry for the 1000+1 questions. But I've seen a lot of cars with PVC systems that make a pretty decent mess where they dump back into the intake and I'm just trying to get my head around what works best.
-scott
As the piston moves upward on the compression stroke, the clearance volume above and behind the top ring are under increasing pressure, which forces the ring outward to improve the mate with the piston wall (better seal=less blowby). A higher pressure differential makes for a greater effect (low crankcase pressure from vacuum pump or header evac, high cylinder pressure from compression or power stroke). Of course, this effect is limited by piston, land, and ring design. Plenty of builders use thin, flexible, low tension rings to reduce friction and better mate with a dynamic cylinder wall, using pressure differential to couple them instead of static spring tension. Gas ported pistons are often used with thin rings and a vacuum pump or header evac, they are complementary.
Certainly, ventilating the crankcase of water or other vapors is desirable in a street engine. With regards to PCV, think about how the vapor/mist is handled... oil mist isn't good in the combustion chamber, but a small amount in a high temperature, low compression street engine generally doesn't cause much trouble, and takes care of a goodly portion of bad guy emissions by burning them. In any engine (though I'm mostly referring to high compression, high performance engines), the crankcase vapor stream can cause problems with preignition or plug fouling, not to mention fuzzy AF ratios from a misbehaving PCV valve coupled with a big camshaft. It can be beneficial to remove vapors in an alternate method, like using a vacuum pump or exhaust flow to draw vapors out of the crankcase and exhaust them to the atmosphere or into the exhaust system. If the crankcase is not sealed, then it may become difficult or impossible to maintain sufficient vacuum to fully utilize the benefits of thin rings and gas ported pistons.
For me, I'm slightly more interested in crankcase ventilation than crankcase depression, but I'm also concerned about moving too much air and sucking oil mist out of the engine (I will use a separator and restrictor) and I don't want the oil mist to pollute my intake (I will use a header evac). Perhaps this is all mental masturbation, but I already see the mess in my intake in my mild 390, and I want to do something different, mostly to get as much margin as I can running pump fuel.
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^^^ Thank you very much for the succinct reply Chad. I'd like to avoid the sloppy mess in my mild 390 intake as well. ;)
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I think Chad hit the nail on the head, but I would add one more point. You don't really need thin rings and gas ported pistons to get the benefits of vacuum in the crankcase. My person experience with this is with the 511" FE that was in my Mach 1 back in 2005. It had nearly stock rings (1/16 - 1/16 - 3/16), and they were standard tension. No gas porting on the pistons. Adding a vacuum pump at the track picked up a tenth and a half, which is pretty impressive on a mid 10 second car. So I think the benefits of any crankcase vacuum, even a lower vacuum setup like the Moroso pan-evac system, are well worth pursuing. I think most of the gains come in the first 5 inches or so of vacuum anyway.