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Opeler
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Discussion Starter #1
I am in need of a threaded vacuum tree fitting for my intake manifold. I know there are a couple of types, I need to be able to use it for brakes, automatic transmission, valve cover pcv, etc.

Thank you,

Eric
 

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Just Some Dude in Jersey
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I never liked the angle that the stock trees position the brake booster hose. I switched to plumbing fittings from the hardware store. I put a T-fitting so that the booster hose fitting points forward, instead of at the heater box, and then a step down out the other end for the auto tranny modulator hose pointing rearwards. Vac advance on a 2.0 or larger engine isn't necessary. The big PCV hose DOES NOT go to the vacuum tree!!!!! You will end up with a massive vacuum leak. The big PCV hose from the valve cover must go to either a small filter to the open air or to a location before the carb/FI throttle body or just to a hose that vents under the car. Some valve covers have a large and a small PCV hose outlet. The small one was meant to go to the intake manifold through a restrictor. Opel later realized that this was unnecessary and deleted the small restricted hose to the intake manifold. Later FI-equipped engine valve covers only have one outlet for the PCV and that should go to a location BEFORE the throttle body.
 

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Opeler
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Discussion Starter #3
I never liked the angle that the stock trees position the brake booster hose. I switched to plumbing fittings from the hardware store. I put a T-fitting so that the booster hose fitting points forward, instead of at the heater box, and then a step down out the other end for the auto tranny modulator hose pointing rearwards. Vac advance on a 2.0 or larger engine isn't necessary. The big PCV hose DOES NOT go to the vacuum tree!!!!! You will end up with a massive vacuum leak. The big PCV hose from the valve cover must go to either a small filter to the open air or to a location before the carb/FI throttle body or just to a hose that vents under the car. Some valve covers have a large and a small PCV hose outlet. The small one was meant to go to the intake manifold through a restrictor. Opel later realized that this was unnecessary and deleted the small restricted hose to the intake manifold. Later FI-equipped engine valve covers only have one outlet for the PCV and that should go to a location BEFORE the throttle body.
That’s what I was referring to.know the large one goes to atmosphere or to be hooked up to the cold air intake prior to the carb, which is how I had it before.

I have both the 1.9 valve cover and 2.2 valve cover. I have been using the 1.9 one because it was chromed and the 2.2 Injection one is painted black. I’d like to get that one chromed, since it will be accurate once I get the Sniper EFI installed.

I don’t run vacuum advance, so I’m not concerned about that. It’s brakes and automatic transmission mainly.
 

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Opeler
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Discussion Starter #4
Scrap that, my bad. I got ahead of myself. All of the vacuum connections actually go right to the Sniper unit, which eliminates the need for the manifold connections. I just need to find a plug for the manifold now.

429284
 

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Thats even better.
 
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You are going the sniper route? Awesome!!!
 

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The big PCV hose from the valve cover must go to either a small filter to the open air or to a location before the carb/FI throttle body or just to a hose that vents under the car. Some valve covers have a large and a small PCV hose outlet. The small one was meant to go to the intake manifold through a restrictor. Opel later realized that this was unnecessary and deleted the small restricted hose to the intake manifold. Later FI-equipped engine valve covers only have one outlet for the PCV and that should go to a location BEFORE the throttle body.
Gordo, we have been around this tree at least twice in the past. On the cars with the 1.9 engine (I cannot speak to the 1.1L), the small hose attached to the vacuum tree draws fumes from the valve cover into the combustion chamber. The large hose from the valve cover draws filtered air into the engine, allowing for the vacuum draw of the fumes. One does not want to have that hose connected to a hose that simply "vents under the car" because, assuming the engine is working properly, the individual with said setup will be drawing unfiltered air into the top of his/her 1.9 engine. That hose is not intended to vent vapors out from under the valve cover -- it is intended to bring fresh air into the engine. This is well-covered in each of the Opel Factory Shop Manuals that I hjave, from 1970-73.. It should be connected to the air intake after the filter, or connected to its own filter.

When I received my GT as a project four years ago, I found the previous owner, having installed the obligatory Weber, left the small hose connected to the manifold, but, without a convenient place to connect the large hose, simply blocked it off! The effect on all of the engine seals was impressive.
 

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Just Some Dude in Jersey
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I was just stating what some guys with alternate intake manifolds and different valve covers do. If you have side drafts of Opel FI, there is no port in the manifold for the wonderous small hose and finding a decent pre-throttle place for the big hose is challenging. The small hose port in the valve cover was deleted in later models, so obviously Opel realized it's pointless. Most side draft dudes take the easy route and vent the big hose under the car. Every worn Opel engine I have ever had BLEW air out of the valve cover. I've never bothered to check the situation on my recent rebuilt engines, but my long time 225K engine was rebuilt when I got it and always BLEW air out of the valve cover from the day it was new until I sold the car 225,000 miles later. I have heard of people plugging up the valve cover holes and they shortly thereafter blew the seals on their engines out. My original yellow painted used 2.4 had so much blowby that it lost a substantial amount of oil through the big hose to a pre-carb location and this was evidenced by oil drenched air filters.

So, what we need to decide this argument is for someone to make a video showing that there is SUCTION happening at the big hose outlet on the valve cover to allow this alledged fresh air INTO the engine. A piece of paper over the hole ought to do the trick. If suction is happening, then where does all this fresh air getting sucked into the engine go? It's gotta go somewhere, is it somehow getting sucked into the combustion chamber via bypassing the rings on the cylinders? If so, then what about blowby? You can't have both. Is fresh air getting sucked into the engine and disappearing into a black hole? Are combustion vapors that blowby the rings into the crankcase also disappearing into the same black hole?
 

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Considering what the small hose is supposed to do, and what goes through it, it stands to reason that, unless properly maintained, it will become plugged and inoperative. The hose and/or the connection on the vacuum tree can become obstructed; the hose itself can deteriorate and collapse; or the filtering mesh in the valve cover can become plugged. When this happens, then, yes, the pressures that build in the system will force oil vapors out of the large hose into wherever you have connected it, including into the filtered air stream where the factory connected it. If this is happening, then the vacuum line requires service.

The circuitry is quite simple: the vacuum draws fumes, including blow-by, out of the valve cover. But in order for this to work, there has to be a supply of air into the system, and that comes from the large hose the is connected to the air induction post filter. There is no "black hole".

Opel did not decide the small hose and its connection to be "pointless". Rather, a more efficient system became required to meet increasingly restrictive emissions requirements.
 

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Each PCV system appears to have some form of restriction into the intake. It can be in the hose nipple as in this case, or in the PCV valve. The pressure in the crankcase varies with engine operating conditions. At idle, and light to moderate cruise, there is typically not too much blowby and so all the blowby can pass through the restriction. At WOT, the blowby increases and if you did not have a restriction, then it could blow oil into the intake.

Think of the 2nd hose into the crankcase as essentially a pressure equalizer, to keep the pressure or vacuum from getting too large. At idle and up to moderate cruise, it is an inlet so you don't suck in the seals. At WOT, the 2nd hose becomes an outlet to the crankcase pressures.. so that you don't blow oil out of the seals.

The '75 system appears to count on the fact that there is always a very modest vacuum level between the AFM and the throttle valve, and that modest vacuum increases in proportion to air flow (engine load). You don't have the large vacuum variations of a carb'd system's intake manifold. The crankcase blowby increases with engie load, so this slight vacuum and the blow by increase together. There is a restriction in the hose nipple in the valve cover to not ever get oil into the inlet tract. But no 2nd hose or inlet for an equalizer, so if blowby gets large, IDK where it goes.

Engine wear is just another variable. With a lot of wear and blowby, there will be a pressure all the time but with a fresher engine, you will indeed find suction into the crankcase at idle with a PCV system in place.

BTW, timely discussion for me; I am ready to change the '75 from the Jetronic FI to dual DCOE's so I need to rethink the PCV function. I am already planning a setup with 4 small restricted nipples, 1 on each throat, and combined in a 4x manifold to create a vacuum source for ignition timing. The brake booster is a very low flow device so it will stay on the #4 throat with a larger nipple.
 

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Each PCV system appears to have some form of restriction into the intake. It can be in the hose nipple as in this case, or in the PCV valve. The pressure in the crankcase varies with engine operating conditions. At idle, and light to moderate cruise, there is typically not too much blowby and so all the blowby can pass through the restriction. At WOT, the blowby increases and if you did not have a restriction, then it could blow oil into the intake.

Think of the 2nd hose into the crankcase as essentially a pressure equalizer, to keep the pressure or vacuum from getting too large. At idle and up to moderate cruise, it is an inlet so you don't suck in the seals. At WOT, the 2nd hose becomes an outlet to the crankcase pressures.. so that you don't blow oil out of the seals.

The '75 system appears to count on the fact that there is always a very modest vacuum level between the AFM and the throttle valve, and that modest vacuum increases in proportion to air flow (engine load). You don't have the large vacuum variations of a carb'd system's intake manifold. The crankcase blowby increases with engie load, so this slight vacuum and the blow by increase together. There is a restriction in the hose nipple in the valve cover to not ever get oil into the inlet tract. But no 2nd hose or inlet for an equalizer, so if blowby gets large, IDK where it goes.

Engine wear is just another variable. With a lot of wear and blowby, there will be a pressure all the time but with a fresher engine, you will indeed find suction into the crankcase at idle with a PCV system in place.

BTW, timely discussion for me; I am ready to change the '75 from the Jetronic FI to dual DCOE's so I need to rethink the PCV function. I am already planning a setup with 4 small restricted nipples, 1 on each throat, and combined in a 4x manifold to create a vacuum source for ignition timing. The brake booster is a very low flow device so it will stay on the #4 throat with a larger nipple.
Good info. I have no experience with the '75 engine, having stopped owning and working on the cars after I purchased the '73 Luxus new, until I acquired my '71 GT four years ago. Got my first experience with the cars as a make-ready mechanic in a Buick dealership in 1968, then purchased new a '70 GT before buying the Luxus for my future ex-wife.
 

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The Crankcase Ventilation System on a CIH engine is somewhat different than most other engines.

On the cars with the 1.9 CIH engine the small hose attached to the vacuum tree draws fumes from the valve cover into the combustion chamber.
Yes, that is true. Not the full story, but true

The large hose from the valve cover draws filtered air into the engine, allowing for the vacuum draw of the fumes. One does not want to have that hose connected to a hose that simply "vents under the car" because, assuming the engine is working properly, the individual with said setup will be drawing unfiltered air into the top of his/her 1.9 engine.
Also true. Definitely NOT the full story. Read on...

That hose is not intended to vent vapors out from under the valve cover -- it is intended to bring fresh air into the engine. This is well-covered in each of the Opel Factory Shop Manuals that I have, from 1970-73..
OK, that is NOT true. The large hose has TWO functions:

1) Supply filtered air into the valve cover while the crankcase fumes generated by the engine are less than the manifold vacuum can draw through the "metered orifice", which causes crankcase fumes to be drawn into the intake manifold and are burned in the engine. The large hose provides "make up air", as otherwise the crankcase would be pulled into a vacuum, and the oil seals will fail prematurely.

2) If / when the engine produces more crankcase fumes than the metered orifice can draw, OR when the manifold vacuum is reduced (such as under full throttle), then the large hose flow REVERSES and the excess crankcase fumes EXIT the large hose, into the air intake, and the fumes are drawn into the carb throat and burned in the engine. If the large hole is plugged on the valve cover, excess crankcase pressure will build, and seals and even gaskets will fail

It should be connected to the air intake after the filter, or connected to its own filter.
Yep, strictly true, but see above for the whole story.

And it should be noted that burning crankcase fumes through a crankcase ventilation system might be environmentally beneficial, but the fumes can cause lowered effective fuel mixture octane, causing premature detonation, and can even cause plug fouling if the engine is worn and there is a lot of oily blow-by
 
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The Crankcase Ventilation System on a CIH engine is somewhat different than most other engines.
This kmight be worth reconsidering... this PCV system is just like pretty much all systems of the day, at least for US designed engines...????? This general design layout is the norm on Ford's, Mopar's, and Chevy's. Only the restriction device is different (the fixed nipple orifice).

And it should be noted that burning crankcase fumes through a crankcase ventilation system might be environmentally beneficial, but the fumes can cause lowered effective fuel mixture octane, causing premature detonation, and can even cause plug fouling if the engine is worn and there is a lot of oily blow-by.
FWIW.... Been wondering on the severity of oil induced detonation for years....My best conclusion to date is that is it not a factor of note for most of us, unless and until you get a pretty fair amount of oil in the chamber. I read one research paper on this today, that stated that their simulated oil detonation events were maximized when the oil in the chamber reached around 1/4 the quantity of fuel at stochiometric ratio. That is a lot of oil and would seem to be a pretty well worn engine.
 

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This might be worth reconsidering... this PCV system is just like pretty much all systems of the day, at least for US designed engines...????? This general design layout is the norm on Ford's Mopars, and Chevies. Only the restriction device is different (the fixed nipple orifice).
The difference to note is that Opel CIH engines of this era did NOT have a PCV valve. Many folks have assumed that their engine is simply MISSING the PCV valve, and jam one into the large hole in the valve cover. Not a good thing to do without understanding what the metered orifice's function is.
 

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I am in need of a threaded vacuum tree fitting for my intake manifold. I know there are a couple of types, I need to be able to use it for brakes, automatic transmission, valve cover pcv, etc.

Thank you,

Eric
Going all of the way back to the first post, there were multiple vacuum trees, depending on the model year and the transmission. Cars with automatic transmission had the extra port for the transmission's modulator valve. Cars in the 73-74 model year had an EGR valve attached below the vacuum tree, necessitating the relocation of the PCV metered port for the small hose to a location on top of the intake manifold on the cylinder head side next to the carburetor. All,of this is covered in one of the excellent writeups on the OGTS website:

Now, my own apology. I was away for a few days and was posting from memory when I said that the function, purpose and operation of the PCV system was well described in the Factory Shop Manuals in my possession. Having arrived back home I checked and found this to be quite untrue. What I "remembered" actually came from a posting that I printed and put into my restoration notes. In point of fact, the FSMs that I have (1970, 71, 73) make almost no mention of this system other than to recommend that the metered orifice for the smaller hose be cleaned (using compressed air) at 6,000 mile intervals. I apologize for the incomplete information.
 
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