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Ed Ruth
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Joined: May 14, 2005
Posts: 343
Location: Bakersfield, California
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 Posted: Thu Oct 07, 2010 4:50 pm Post subject: |
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These are sound arguments and well stated. I suspect, however, that it may well be better to have an unrestricted vent somewhere, however small it may be, to prevent pressure extremes should they occur for whatever reason. How is an intake air preheat made?
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Sage79
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Joined: September 13, 2008
Posts: 437
Location: Holland MI
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| Posted: Thu Oct 07, 2010 5:22 pm Post subject: |
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It sound to me like Ray and SGKent have opposite opinions of the normal crankcase pressure and hence do not agree on how the valve operates. For clarification: negative pressure (compared to ambient or atmosphere) is vacuum and positive is pressurized. Are we all using the same terminology? SGKent: how does the valve prevent the case from becoming a vacuum can if the valve only opens under positive pressure? That sounds more like what Ray is advocating. Something doesn't add up here. Since it is a differential pressure valve it is comparing the pressure on the intake to the pressure on the crankcase. I assume the manifold pressure is always negative but to a varying amount, either more negative or less negative. The crankcase pressure seems to be where you guys are talking past each other.
I'm confused 
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Dirk
'79 Westy 2.0FI
'73 Sportsmobile 1.7dual Solex 003Auto - now my daughter's
'77 delux 2.0FI 090Auto - now my son's |
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Wildthings
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Joined: March 13, 2005
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| Posted: Thu Oct 07, 2010 7:35 pm Post subject: |
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Presuming the T4 FI valve works the same as the WBXer Vanagon valve, it works (mostly at least) on the pressure differential between the crankcase pressure and ambient air pressure not the pressure of the intake air stream between the throttle body and the AFM. It certainly does not read manifold vacuum at all. There is a small area of the diaphragm exposed to vacuum drawn by the AFM, but it is small in comparison to the area of the diaphragm exposed to the crankcase pressure.
You almost never hear of a problem caused by the Bay valve not operating correctly and from personal testing I have been unable to detect any difference in how a Vanagon engine operates when the diaphragm fails in the valve and the valve effectively stays open at all times. The Vanagon does of course have an O2 sensor, which might negate any negative affects the bad valve might cause. |
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SGKent 
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Joined: October 30, 2007
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Location: at the beach
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| Posted: Thu Oct 07, 2010 10:03 pm Post subject: |
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It sound to me like Ray and SGKent have opposite opinions of the normal crankcase pressure and hence do not agree on how the valve operates. ... SGKent: how does the valve prevent the case from becoming a vacuum can if the valve only opens under positive pressure?
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The valve in question is on an L-Jet FI system. 75-79 buses and some other VW cars. The Porsche 914 system Ray describes as a metered orifice was on carbed T4 engines and it works completely different.
If you are in a smog state and have a smog year bus then you cannot vent the crankcase to the atmosphere. If you are in a non-smog state you could seal off the S-boot breather opening and vent the PCV breather into a catch can.
The reason the oil cap cannot be left off or leak on an FI bus with the stock breather is that air will enter the oil tube, flow through the engine, out through the breather and into the S-Boot which will be unmetered air as it is bypassing the AFM. This will grossly throw off the A/F ratio.
The round valve has a spring and a diaphragm in it. The spring is = 1 atmosphere. When the crankcase has less than 1 atmosphere of pressure in it (a vacuum of any amount, the small spring is overcome by the diaphragm to hold the valve closed so the s-boot cannot pull a vacuum in the engine case. When the pressure is equal to or greater than 1 atmosphere inside the case, e.g. when there is blowby, the positive pressure pushes against the diaphragm which with the help of the spring opens the valve, allowing the vacuuum in the S-boot to draw out the blowby. As soon as the pressure in the case is <1 atmosphere again the valve closes. When the diapgragm rots away then there is a direct connection between the engine case and the S-boot so the S-boot can pull as many inches of vacuum out of the case as what is in the S-boot. With a rotted valve diaphragm if you have 17" of vacuum in the S-boot you have 17" of vacuum in the case. This causes more blowby and pulls oil away from the rings and guides, causing more wear.
Ray is suggesting using a metered orifice system similar to the 914 engine so that the flow is restricted but open all the time. His method will work well with a carbed engine and reasonable well with the L-jet however IMHO the original design is better if you can find a good PCV valve (the round valve on the top). The point that is most critical is that you cannot operate FI properly while you have a rotted PCV valve or leaky oil cap.
A photo of the insides is below. The red arrows show the direction of blowby flow.
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Wildthings
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| Posted: Thu Oct 07, 2010 10:40 pm Post subject: |
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You are grossly off in even suggesting that the S-boot could see 17 inches of vacuum. The S-boot is upstream of the throttle valve and will only see a small vacuum, whatever the flow resistance through the air cleaner and AFM is. I don't know what the actual maximum vacuum seen in the S-boot is, but it is probably much much closer to 1 inch of mercury than 17 inches.
The presence of the small spring also indicates that the valve does not operate at 1 atmosphere but at some slight differential to it. |
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Sage79
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Joined: September 13, 2008
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Location: Holland MI
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| Posted: Fri Oct 08, 2010 4:49 am Post subject: |
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SGKent that explanation makes complete sense. The 17" I'm sure is an exaggeration which illustrates the point.
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Dirk
'79 Westy 2.0FI
'73 Sportsmobile 1.7dual Solex 003Auto - now my daughter's
'77 delux 2.0FI 090Auto - now my son's |
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raygreenwood
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Joined: November 24, 2008
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Location: Oklahoma City
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| Posted: Fri Oct 08, 2010 7:45 am Post subject: |
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| SGKent wrote: |
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It sound to me like Ray and SGKent have opposite opinions of the normal crankcase pressure and hence do not agree on how the valve operates. ... SGKent: how does the valve prevent the case from becoming a vacuum can if the valve only opens under positive pressure?
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The valve in question is on an L-Jet FI system. 75-79 buses and some other VW cars. The Porsche 914 system Ray describes as a metered orifice was on carbed T4 engines and it works completely different.
If you are in a smog state and have a smog year bus then you cannot vent the crankcase to the atmosphere. If you are in a non-smog state you could seal off the S-boot breather opening and vent the PCV breather into a catch can.
The reason the oil cap cannot be left off or leak on an FI bus with the stock breather is that air will enter the oil tube, flow through the engine, out through the breather and into the S-Boot which will be unmetered air as it is bypassing the AFM. This will grossly throw off the A/F ratio.
The round valve has a spring and a diaphragm in it. The spring is = 1 atmosphere. When the crankcase has less than 1 atmosphere of pressure in it (a vacuum of any amount, the small spring is overcome by the diaphragm to hold the valve closed so the s-boot cannot pull a vacuum in the engine case. When the pressure is equal to or greater than 1 atmosphere inside the case, e.g. when there is blowby, the positive pressure pushes against the diaphragm which with the help of the spring opens the valve, allowing the vacuuum in the S-boot to draw out the blowby. As soon as the pressure in the case is <1 atmosphere again the valve closes. When the diapgragm rots away then there is a direct connection between the engine case and the S-boot so the S-boot can pull as many inches of vacuum out of the case as what is in the S-boot. With a rotted valve diaphragm if you have 17" of vacuum in the S-boot you have 17" of vacuum in the case. This causes more blowby and pulls oil away from the rings and guides, causing more wear.
Ray is suggesting using a metered orifice system similar to the 914 engine so that the flow is restricted but open all the time. His method will work well with a carbed engine and reasonable well with the L-jet however IMHO the original design is better if you can find a good PCV valve (the round valve on the top). The point that is most critical is that you cannot operate FI properly while you have a rotted PCV valve or leaky oil cap.
A photo of the insides is below. The red arrows show the direction of blowby flow.
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No....the parts I am speaking of have nothing whatsoever to do with carbs.
100% of all fuel injected 914's with 1.7L type 4 and 100% of all 1.7L type 4's in 411 and 412's...have crankcase under vacuum. This is D-jet fuel injected I am speaking of. I realize you are speaking of L-jet. The valve you are illustrating...is L-jet fuel injected.
The point I am trying to clarify of all of those who are watching this thread......is that your comment that having the case under vacuum pressure wears out valve guides and rings.....is ONLY possible or correct....on L-jet injection and not all engines in general.
This is because.....D-jet injection has a fresh air intake through a normal PCV valve...from which to pull incoming air. Therefore it is 100% impossible to EVER pull air and gasses through the valve guides or past the pistons.
I know exactly how the L-jet relief PCV valve works. And....unlike the D-jet I described above.....L-jet is a CLOSED system. It has no fresh air relief. Having high vacuum on an L-jet case with the standard L-jet PCV valve that is shown in the pictures above.....could indeed pull gasses past the valve guides and rings.
The method I am suggesting,....has nothing whatsoever to do with carbs...and was never used on any carbed vehcile in any type 4 engine.
The carbed PCV system was variation, but is signifcantly different in both the oil baffel and the fact that carbed 411/412 (which never came to the USA)and 914's (which never came to the USA except gray market...with no PCV) used no PCV valve and no metering of the incoming air. Which is also why they were lousey at generating vaccum for advance.
However this system ... was used on all D-jet injected type 4's ever built. It is simply the factory flow through PCV system...with a fixed orifice instead of a sping loaded PCV valve....and works perfectly...and about 1000% better than what came on L-jet.
However....the PCV system I am describing cannot be easily slaved to an L-jet system because the L-jet system...uses airflow for metering. Pulling vented fresh air through the case using manifold vacuum will bypass the airflow meter...causing lean running with L-jet.
It can be used on L-jet.... if you use an a source of vacuum other than the manifold downstream of the TB.
I suggest you guys crack the books and study up on the PCV and venting systems the factory used on the type 4 system. It will be enlightening. Ray |
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Hoody
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Joined: November 28, 2007
Posts: 1948
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| Posted: Fri Oct 08, 2010 10:19 am Post subject: |
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| Hey Steve, I think it's time to reproduce those silicone diaphragms! |
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SGKent
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Joined: October 30, 2007
Posts: 42511
Location: at the beach
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| Posted: Fri Oct 08, 2010 10:45 am Post subject: |
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| You are grossly off in even suggesting that the S-boot could see 17 inches of vacuum. |
There is a door in the AFM on the other side of the S-Boot. It remains closed until a vacuum opens it. Fuel Injection Corp uses 20 inches of vacuum at the AFM side of the S-Boot to test them. Mine shows 18-19 inches. If the AFM door was not there and it went straight to the air cleaner then there would be no vacuum but that little door changes all.
If you do a search you will see there are threads on it already. That is why s-boot cracks are so fatal to the engine running on an FI bus.
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SGKent
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Location: at the beach
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| Posted: Fri Oct 08, 2010 10:57 am Post subject: |
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| Hey Steve, I think it's time to reproduce those silicone diaphragms! |
I gave up. There were maybe 10 that I had buyers for. With a minimum cost to produce about $1500 that would have been $150 each diaphragm . It only cost $46 each for the two new valves from Europe several months ago but I think Bobby got the last two. Besides the community chased him away. He helped me with these valves and genuine old stock center link bushings - not to mention some of the impossible to find small heater cables and parts.
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SGKent
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Joined: October 30, 2007
Posts: 42511
Location: at the beach
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| Posted: Fri Oct 08, 2010 11:06 am Post subject: |
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| The 17" I'm sure is an exaggeration which illustrates the point. |
no. See my post above. The area between the plenum and the AFM door acts as one vacuum area when the throttle body butterfly is wide open. The door maintains the vacuum level. The pressure between the air cleaner side of the door and the S-Boot side of the door is what opens the door. The only time vacuum is higher in the plenum than on the S-boot side is at idle when the throttle body butterfly is closed. There is a balancing act between the plenum, S-boot and AFM door.
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Wildthings
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Joined: March 13, 2005
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| Posted: Fri Oct 08, 2010 12:15 pm Post subject: |
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I have never seen any engine that ran a manifold vacuum even close to 17" of mercury at wide open throttle, if it did then there would be major power gains to be had by changing out the AFM and air cleaner with something bigger and better, and almost every last T4 engine would have had this "improvement" by now. That almost nobody does this is proof enough to me that the vacuum in the S-boot is nowhere close to 17" mercury.
Holley rates their larger carbs at 1.5" of mercury IIRC and their smaller carbs at 3.0". It would take one heck of a pump to draw 17" mercury on a bore the size of the AFM on one of these rigs. |
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raygreenwood
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Joined: November 24, 2008
Posts: 23130
Location: Oklahoma City
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| Posted: Fri Oct 08, 2010 12:50 pm Post subject: |
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| SGKent wrote: |
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| Hey Steve, I think it's time to reproduce those silicone diaphragms! |
I gave up. There were maybe 10 that I had buyers for. With a minimum cost to produce about $1500 that would have been $150 each diaphragm . It only cost $46 each for the two new valves from Europe several months ago but I think Bobby got the last two. Besides the community chased him away. He helped me with these valves and genuine old stock center link bushings - not to mention some of the impossible to find small heater cables and parts. |
If you have a complete diaphram....even if its rock-hard....but complete....I cna make a mold for it. If you are injection molding the mold will have to be steel...hence the high cost.
If you are using a combination of low pressure and high vacuum...I can make a precision polymer mold for about $60. It should be accurate to about .0003" to .0005". It will even have thestock part #'s.
I would use high temp, medium viscosity pourable silicone. Pumped in with a clean grease-gun type pump at about 200 psi...with about 20" of vacuum on the vent. The silicone product would run about another $85...but would make about 200 diaphrams. Ray |
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Ed Ruth
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Joined: May 14, 2005
Posts: 343
Location: Bakersfield, California
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| Posted: Sun Oct 10, 2010 9:46 pm Post subject: |
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This short movie will show, if you watch until the end, that there is a slight vacuum inside the engine...at least at idle. http://www.youtube.com/watch?v=7jU_JOm4BPg
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webwalker
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Posts: 2803
Location: Mount Laurel, NJ
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| Posted: Fri Mar 25, 2011 6:33 pm Post subject: |
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| I would use high temp, medium viscosity pourable silicone. |
So Ray, did you ever decide to pursue this?
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raygreenwood
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Joined: November 24, 2008
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Location: Oklahoma City
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| Posted: Sat Mar 26, 2011 12:24 pm Post subject: |
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| Sure...i would love to! No one ever contacted me. I don't drive L-jet so persionally I have no use for this diaphram...but I would be happy to repro a few if someone sends me one for a mold. Ray |
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curtis4085
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Joined: July 22, 2011
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Location: Colorado
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| Posted: Mon May 07, 2012 7:54 am Post subject: |
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Hello all. Am writting here today because I'm in severe desperate need for the oil breather pcv valve for my 79 FI bus and had no luck on the search. I'm currently in Cali knee deep in family issue caring for my grandfather 24/7 which has slowed, rather stopped my search. If anyone could please help I would be forever in your debt. Would gladly pay up to $500 bucks for a NOS part if someone has one or can make a connection to one please PM me. I sorry for posting here but am very desperate with zero energy to focus on this.
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Busstom
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Location: San Jose, CA
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| Posted: Mon Aug 17, 2015 12:41 pm Post subject: |
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Has there been any resolute consensus on the fix for this? A firm, certain replacement that works as the original, or a "fix" that's easy and undisputed by the legions of forum users?
Sorry to resurrect this, but hours of reading the history here has yielded no satisfying solution. Because, dig this: I go to look at a '75 Westy, for the second time...looking closer this time, and with plans to bring 'er down the ranch road onto paved roads so I can really decide to buy it.
Being a Bay/T-IV newb, what do I do? I reach into the engine compartment and grab on something that looks like a cap, and what do I do? I snap the fricking crankcase prv apart! On a vehicle I don't even own!!!
So I tell the dude, "Well, I'm basically gonna buy it anyway..." Yeah, no sh*t.
For what it's worth, it's smog-exempt here in California, and so the question is: Can I just plug the S-boot and run a typical Type 1 breather? And then adjust the FI accordingly?
I can't believe the related discussions are years old, and there is no post about a sure-fire fix...at least that I've been able to dig up. |
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SGKent
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| Posted: Mon Aug 17, 2015 12:59 pm Post subject: |
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the purpose is to keep the case from becoming a giant vacuum can. You'll want to keep FI so you will need one of those. FWIW if the cap came off someone already pried it apart. The seam is heat welded and it takes quite a bit to get them apart. There are people who can make the diaphragms but the problem is cost. We'd need about 300 - 500 orders for the whole unit to make it really financially feasible. It would probably be better to redesign it in aluminum and made a top that screws on using a piece of special fabric. As for NOS ones, I know of only 4 that have been found in the last 7 years.
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Busstom
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Joined: November 23, 2014
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Location: San Jose, CA
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| Posted: Mon Aug 17, 2015 10:28 pm Post subject: |
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| SGKent wrote: |
| FWIW if the cap came off someone already pried it apart. The seam is heat welded and it takes quite a bit to get them apart. |
I don't think so...the whole plastic part broke off in my hand, as I gave it several pounds of cranking force. Honestly, I don't know what the hell I was thinking, I'm generally not a hack like that.
Anyway, are all engines running basic breather boxes to atmosphere "vacuum cans," as you put it?
All fuel injection aside, what is different about the blow-by and crankcase pressures in a type IV as opposed to other engines? And if it's not, then what is it about the L-jet FI that requires it to breathe crankcase gases? |
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