Engine breather

Dr.Jeff

Dr.Jeff

True Classic
The whole "cyclone filter" engine block breather / oil separator-return assembly has been discussed in the past. But I've never seen this question asked.

If maximizing engine ventilation ("breather" function) was the specific goal (for any reason). And the vent hose was not connected to the intake, but to a large 'catch can' with a large filtered vent to the atmosphere. And the largest possible hose (without the screen installed) and fittings were used to do that. Would it be any advantage to remove or otherwise alter the lower tube (oil return pipe) on the bottom side of the cyclone/separator? I'm referring to this part:
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It drains any captured oil back to the oil pan by extending from the bottom of the cyclone down to the oil level. But that would seem to reduce the actual ventilation capability, because it is the only passage between the crankcase and the breather. Either removing it completely or otherwise modifying it to allow a direct passage at the bottom of the cyclone should offer better breathing.

And there does not seem to be any other means of ventilating the block. So another possibility is to add a second vent at the rocker cover.

Any thoughts? I may not have provided all pertinent details, so I'm sure there are questions. Thanks
 
Are you trying to solve a problem that does not exist? I'm not aware of anyone complaining that their crankcase does not vent properly. The very fact that the large rubber vent hose goes to the aircleaner suggests there is not a super high volume of fumes in normal operation. If the engine rings are worn, that may be a different issue but again that's not the vent problem it's a piston ring problem.
 
Turbo engines have more crank pressure. But honestly I was trying to avoid the reason because that is not the question at hand. This is hypothetical and wondering if there might be a big difference in block ventilation if the lower tube was removed.
 
Not good to remove the drain tube. It is situated below the oil level to prevent CC pressure backfeeding that, which would of course negate any oil draining post separation from the CC gases.

Just leave the cyclonic trap & use a straight hose with no flame trap if you want to VTA. The orifice is sufficient ID for the motor capacity, even with light pressure turbo which is the plan, correct?
 
lookforjoe said:
It is situated below the oil level to prevent CC pressure backfeeding that, which would of course negate any oil draining post separation from the CC gases.
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That is why I was thinking about removing the pipe; because it extends below the oil level, and there is no other opening to the cyclonic trap, the gasses have to pass through the oil to get to the trap. That would make venting of gasses more difficult. It would also collect more oil as it travels through the pan, sending more to the catch can. By removing the pipe (or at least shortening it to above the oil level), the gasses can flow freely through the passage to the trap. Essentially I'm talking about converting it from a oil separator to a true crank case vent, which I will need. I'd rather have more ventilation than worry about trying to scavenge a bit of oil vapor. And actually it might have less oil going through the vent due to the lack of gasses having to pass through the oil first. At least that is the theory, but I am open to alternative thoughts. The biggest aspect as I see it is the fact there is no other path for the gasses to travel except down through the oil in the pan first, then up the tube - like a perculator. Am I missing another gas vent path somewhere? Thanks
 
Are you sure the trap is connected to the oil return pipe, I thought there is hole in the block next to the trap retaining bolt and there is no connection of the trap to the return pipe. I don't have any bare blocks laying around to verify this.
 
carl said:
Are you sure the trap is connected to the oil return pipe, I thought there is hole in the block next to the trap retaining bolt and there is no connection of the trap to the return pipe.
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I assumed the same thing, it only seems logical to be that way. But on my '85 block there is only one passage between the cyclonic assembly and the block. That is the drain tube. And that tube is a sealed connection to the cyclonic assembly. So there is no other path than through the oil. I guess there isn't enough crankcase pressure on a stock engine to need more.

And as I'm thinking about it, there may be another reason it is this way. The Bosch EFI is very sensitive to vacuum leaks, due to the function of the flapper air box to determine fuel mixture. So if there was a open vent from the crankcase to the intake - downwind of the flapper - it would throw off the mixture (like a vacuum leak). I guess the cyclonic assembly really isn't much of a vent at all, but more a air/oil separator.

When I finally get to tearing down my carbed '79 block it will be interesting to see if there is any difference in this design. It might have a second passage to the cyclonic assembly from the block. But that won't be for a while.
 
If the tube is the only exit, then vapor pressure buildup in the crankcase would force oil up the pipe until the level of oil in the pan is forced down to the inlet end of the tube, finally allowing the built up gas an escape; I do not think this is what happens in there.
Personally, I believe the tube is an oil return from the separator.
 
The tube is a oil return for the separator. But there us no other passage or connection to the separator, so the tube must also be the vent. I'll try to take pictures but it is a dark recessed area and not much to see.
 
Jeff,
There are two openings to the bowl under the cyclonic trap.

The bottom on the bowl has an opening to the drain tube, and a threaded hole for the bolt, then on the front side of the bowl is an additional opening. Looks like it goes toward the mechanical fuel pump location.

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That certainly makes more sense Andy. Perhaps that hole is covered in grime on this block (it is pretty foul inside), because it does not appear to exist. I will look closer and poke with a scribe to see if I can uncover it.

I also just saw a illustration in the FSM that indicates there is a passage in addition to the drain tube, but it is not an accurate drawing so it's vague where that is. But after seeing your picture I'm sure that's it.
Thanks for pointing it out.

So back to my question. Do you suppose it will allow better block ventilation it that hole is enlarged, or the drain tube left off to provide a second hole?
 
I would think just cutting a hole in the side of the tube above the oil level (on the side away from the moving internals perhaps) would be enough.
 
You still don't want to do anything to negate the drain back function. Unless you really want to push oil out the motor with the CC gases.

I played around with engine beather mods extensively on my old wagon, primarily due to the much larger turbo and rpm increase to 9K+. The higher the pressure you run on the turbo, and the higher the rpm range you run, the more CC gases you will generate. If you don't allow some way for the oil/vapor to be separated you will be consuming oil at a rapid rate. It will literally pump the oil out the vent.

If you do away with the trap altogether and do a straight VTA, that will indeed minimize pumping losses BUT you will be pushing oil out the vent, AND it stinks to high heaven. Obviously having a properly baffled catch can will collect the oil that would normally drain back into the motor. Depending on how you drive, you may need to empty it within a few miles. I filled a quart container in a single 1/4 mile pull.

The bottom line is, IMO, there is zero reason to remove the cyclonic trap on this motor, and absolutely no reason to remove the drain. It does make sense to make sure the vent passages are thoroughly clear, as it sounds like yours are likely clogged.
 
Enlarging the vent hole between the crankcase and the cyclonic assembly, and/or adding a hole to the side of the tube or even removing it altogether, would not negate the drain back function as far as I can see. Oil will still drain down the same hole that the tube fits in. I believe the only function of the tube is to guide the draining oil away from rotating parts (which is a good thing to do). So we are not talking about removing or doing away with the cyclonic trap, just opening up the size of the vent passage to it from the crankcase area, to allow a freer flow of pressure.

I imagine the size of the engine, turbo, amount of boost, operating RPM range of the engine, condition of the rings, etc, all have a major role in the amount of oil that is pushed out. In the referenced case of the Volvo wagon I believe the boost pressures were quite high? And you mentioned running at higher RPM's. So that engine would likely have more oil going out than a stock SOHC 1500 with a small turbo. But the point is well taken, I am surprised (as I'm sure you were too) at how much oil you found in the catch can. That will definitely go into the consideration of how things are designed.

Now that I better understand how the cyclonic assembly works (realizing there is a second passage to it from the crankcase, as it should be), I'm thinking the better approach will be to just enlarge that second hole (passage). Make it closer to the size of the passage from the cyclonic trap to the catch can. Leaving the drain tube in place. As noted previously, I could not see the second hole in my old dirty block, so I was thinking the drain back tube was the only vent (which really seemed odd to me as well). And that is where the thought of removing the drain tube came from. However that is no longer the understanding.

Really appreciate all the input.
 
Leave the drain tube in... all the right reasons for leaving it alone already stated.

If you want to vent the crank case more, use the fuel pump hole, which for your fuel injected engine has a block off plate that will fit another 3/4 hose to if you braze a fitting on there... or you could buy a pre made fuel pump blockoff / breather, I get them from Bojan in Croatia (Stole's race shop on ebay)

A racers trick is to plumb the crankcase breather (after the catch can which is then not vented to atmosphere) into a low pressure area of the exhaust, and actually create a slight vacuum inside the crankcase, plus it "disposes" of the vapors ... not too sure if this would work on a turbo engine though.

SteveC
 
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fiatfactory said:
A racers trick is to plumb the crankcase breather (after the catch can which is then not vented to atmosphere) into a low pressure area of the exhaust, and actually create a slight vacuum inside the crankcase
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I recall when this was done, a nice little check valve item is added to the connection at the exhaust, angled to follow the exhaust gas flow. Prevents any exhaust gas flowing back to the crankcase. It is actually a common part of standard smog/emissions equipment (NAPA 2-29000). [Second pic is with a turbo system]

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The problem with tapping into the exhaust is that the precise depth and angle is critical. I did also try that, and I did not find it successful. I didn't bother with a check valve, as that also can just create more issues depending on the crack pressure. Doesn't really work well if you have a cat, as the oil will definitely contaminate the core.

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fyi, I did this on one of my 124 race cars years ago, it worked too well, I did not eliminate the tube and sucked oil from the oil pan through the breather was a real mess, took out the pipe and it worked great. helps ring seal with light tension rings. would not help with stock stuff too much
 
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