I was looking at the factory manuals and talking with someone about crankcase breathers. We were talking about breather setups for carbs specifically. And I realized as I was looking at the breather diagram that it appears that the breather ports on the heads were included to supply extra air to flow through the engine case. And then I read this little snipped in the manuals which seems to support my thought:



So following that logic...
If the crankcase breather (at the oil filler neck) isn't connected to a vacuum source, then the ports at the heads should/could be plugged instead of connected to a breather box.

Thoughts? Contradictions? Agreement?


I realize people have been connecting breathers all sorts of different ways and most work just fine. I'm more interested in the theory aspect, and refining an 'ideal' installation since we already know many ways to 'make it work'.

From my limited experience the head vents *suck* air until you get to higher rpm (5k+), at which point there seems to be enough pressure in the case to reverse the flow.

That was on my carbed 2056 ...

I always want the crankcase ventilation to be just that. Venting the crankcase. I'm afraid that the venting of the heads inhibits oil drainage back into the crankcase and may, in fact, exacerbate oil loss.

Just my 2 cents...

I had crankcase and head vents tied directly into my air filter lids until recently when I installed Gold Wing air filters. Now I tied the 2 head vents together with a single hose (what I read from Jake Raby a while back) and vented the oil filler housing overboard (thru tin under the engine). Eventually I want to get a breather can for the oil housing vent. I drove the car to ~1800 miles to WCR and back with no adverse effects that I know of. Didn't use any oil that I could tell and I had expected it to use about as quart based on previous trips with the old configuration. I'm leaving tomorrow for RRC and that will be about 2K miles with the new configuration. I'll report back if the results were not the same as WCR. I have a 1911cc with webers.

It could inhibit drainage if there is no vacuum source on the breather, since that configuration would make all ports into exit ports.

But on a plenum based engine with the case ported to manifold vacuum, are would almost always be sucked in the heads and flow down the pushrods tubes to the case, which would aid drainage.

To really compare anecdotes we need some pertinent info:
1. Heads ported? Where to?
2. Case ported to vacuum? (Air filters are not vacuum, ever)
3. Functional PCV valve?
4. Stock-ish or Wild engine?

In my last build, Jake's recommendations at the time were to close off the head vents and run a larger vent from the chimney. Now, I'm dry sumped too, but a -10AN modded "chimney" to a breather is all I have for the motor.

http://hamheads.com/type4-test.php

Here's some info on it....

Interesting ...

I think I had read that before, but it was a good refresher. Unfortunately, it doesn't address a stock type system where the breather 'chimney' is connected to manifold vacuum.

I would agree with Jake and Len for non-vacuum-breathers. But if the filler neck is connected to manifold vacuum, the head ports should be connected to filtered air supply.

Sounds about right to me. On my 2056 with ITB's I've got the heads plugged per Len and a single line off the filler neck to a tangerine racing catchcan. No issues noted.

I.d agree in a stock aystem. Manifold vacuum equalizes the pressure in the rocker chamber by drawing filtered air into the rocker chambers up and out the chimney and into the intake to be burned.

Interesting that they tested it with a dry sumped motor.

My quess is that it was equalizing in the chimney depending on the crankcase pressure.....and if aerated enough into the puke can.

Just found this in the 1975 Emissions book that came in the glovebox with the operation manual. Oddly it shows the filler neck vent connecting to the air cleaner, and the head vents connecting to what appears to be the plenum, which is completely backwards to how we know the system is hooked up. But it does show that the air flow is intended to flow into the heads and out of the filler neck.

I like how they show air going two opposite directions in the same line. Might it be that they expect the air to oscillate and eventually particulate matter would be sucked into the intake?

I also am wondering about the term flash arrestor used for the T that connects the two rubber lines from the heads. Is that so a backfire cannot ignite the case vapors?

Also an anecdotal evidence is that when I initially plugged a set of earlier 2.0 head vents the D-jet ran fine. But when the plugs popped out (undetected by me on the way home from Rt66 I had oil all over the place running at 3000 RPM. So I am thinking there wasn't a lot of suction going through them. At least as I hooked up the oil breather, which went to the air cleaner I think.

You're looking at those diagrams all wrong Mark. The passages leading to the heads are intake runners not rocker box vents.
The only crankcase ventilation in both pics is the one at the filler tower.

Your right. That's stupid.

So, what setup for carbs would you suggest to suck the most oil out of the valve covers and back into the case?

I ran hoses from both head vents to a T and to one carb. I found some cloth braided hose at NAPA that looks like it could've come from the factory, and not too expensive

But what method works the best?

Stock FI engine I'd just put it back stock, head vents I block if I can, but I do whatever is easier.

Performance I've hooked them up with head vents and without and never noticed any difference. Most times I prefer no head/rocker vents.
I've always vented to the carbs (or ITB) through the air cleaner with no ill effects. An added plus is no fine oil mist covering the whole engine.
On the bugs and even my bug with the big T4 my breather is just a box, top hose goes to the carb air cleaner, bottom hose drains back in the case, vents are in the middle.
Never seen a problem with draining back to sump or venting to the carbs.

The /6 guys don't like to drain back to the sump, the only reason my /6 puke can has a drain valve to empty the can.

Mark...but aren't you sending that fine oil mist into the carbs?
That can't be good?
Mike

My engine was built by FAT Performance 14 years ago. They included a Bugpack breather they said to mount high on the firewall. They installed (or had already been installed) head vents. They advised that I install hoses between the head vents and the side ports on the breather and between the oil filler neck and the center port of the breather. I'm guessing (because I never kept track) that the engine has between 40 and 50 thousand miles and still runs great. 147 hp @ 5300rpm. I don't know if this is the best way to do this but I do know that it has worked great for a long time. I just thought I would add some more anecdotal food for thought. Plus I like posting pictures of my car.

I'm thinking about doing this with my carbed 2366. Any downsides to this approach?

Building engines since 1990, not once have I seen a downside. OEM systems have been doing the exact same thing for ages. Over the years I done many top end jobs on engines I've built, T1 & 4 performance engines I always dump the vent into cylinder #3, straight down into the throat. Not once have I seen any difference in the intakes or combustion chambers, no unusual coking, no excess oil, no wear difference...nada.

It's a very fine, highly atomized mist and a small amout, it's not like you're burning the oil for fuel.

If you do feel it's causing an problem it's much more likely to be another issue such as worn valve guides.

I found http://hamheads.com/type4-test.php pretty convincing, as well as Mark Henry's experience.

Based on this thread, I'm considering

1. Capping the rocker vents, or tying them together. (Could some kind soul point me to benefits of the latter option?)
2. Chimney to breather to air cleaner. Or could it go directly to the manifold instead of the carb (see below)?

What are these for, anyway?
Click to view attachment

Someone added those as vacuum ports. Most likely the manifolds spent some time in a VW bus and those were used to provide vacuum for the vacuum assisted master cylinder.

BTW I see you have 914 2.0 heads and you have the stock phenolic spacers. The aftermarket manifolds are thicker than the factory FI intake runners and is why your studs are too short. You're only hanging onto the manifolds by a couple of threads, I would recommend replacing the stock studs with 5-10mm longer studs.

Ah... thanks for that info.

Would it be advisable to use those ports for crankcase ventilation?



Yes, thanks. That's been bugging me.

.? Is the hose to the oil filler port going through a pvc or just straight into the oil filler?

Brake boosters have a sealed diaphragm and a check valve. If you hooked that up to the crankcase I believe it would create a huuuge vacuum leak.

No.

Manifold vacuum signal to the 123 distributor?

I could be wrong but I believe you have to find a ported vacuum signal. I think ported vacuum is from above the throttle butterfly on the carbs. My Dellortos don't have a ported vacuum port. I went with centrifugal advance so that I wouldn't have to figure out how to drill carbs for a vacuum signal.

Mark...I have pretty much the same situation. Is there anything special about those studs? Where can I find the longer version?
Thanks

Mark, that is interesting. I have the CB style manifolds (with the three hole web between the runners) on my car and the studs are long enough. I guess the flanges at the heads are not as thick as those in the photo. Are the manifolds in the photo from Pierce Manifolds?

http://www.piercemanifolds.com/product_p/99004.822.html

I have no practical experience with this, so just going from what I'm reading. Nearly everything I'm reading suggests manifold vacuum would be the more useful signal to the distributor. In stock engines manifold vacuum advances the spark when there is a lean mixture at idle or low throttle on the highway. According to what I read, advance is useful then because lean mixtures burn more slowly, benefiting from the head start of an earlier spark. I think we wouldn't want that advance for open throttle because the richer mixture would be prone to pre-detonation.

In the 80s I had a 914 2.0 with the stupid single progressive carb and a Bosch 009. In the Arizona heat, the car would ping unless I dialed the advance back so far it affected performance.

With a non-stock camshaft (like my Web cam) the vacuum would be weaker, but I'm speculating that the 123 distributor could be configured over Bluetooth to compensate for that. Anyway it seems fun to experiment with.

I don't doubt that Vacuum advance may be a better set up. I just didn't want to try to drill my carbs and I am pretty sure that you cant use the vacuum signal from the intake manifold. I have never seen a car with vacuum advance that didn't have the signal coming from somewhere on the carb. Plus I have two carbs and four throats so where do you pull the signal from....just one, both or all four?

I have a mechanical advance that is very adjustable. It is set to 12 degrees at idle and to 28 degrees all in at 2500 rpm. I have a little over 9-1 compression ratio with a WebCam and my car never pings. I usually run it on regular gas. My head temps run around 275 most of the time even in the heat of the summer.

This is from a different forum:

You can't get distributor suitable vacuum from the intake manifold. You would have to drill the carb body, and *VERY* accurately put a TINY hole in precisely the right spot inside the carb throat, where the butterfly meets the wall when it's in the "almost closed" position. That's where the vacuum is strongest. Throttle closed, you have almost no vacuum there, while in the intake manifold the vacuum is then VERY high. (=all wrong).

Some carbs like the Dellorto DRLA's have a vacuum port ready, but sometimes the same model of carb has just a blank hole where the fitting would be. You would need to drill the cover plug out and fix a fitting in there, the hole itself is already there.

The problem: the vacuum you get from dual carbs is not a smooth, combined vacuum created by all 4 cylinders, but a more pulsating vacuum from just one or two cylinders per vacuum port. The amount and quality of vacuum most likely isn't suitable for the distributor.

Click to view attachment

I've always used mechanical advance on dual carbs, but I've heard of peeps using vacuum advance. no idea if it worked well for them. I have seen vacuum used for the bus brake MC, you have to pull off all the runners to get a steady signal. For a dizzy I would also use all four and maybe try running to a small can and take the dizzy vac from that can.

Below shows where to pull vac from a weber IDF.

Do type 4 engines use a negative crankcase ventilation check valve?

Also if the cylinder head vent tubes are capped does air pressure build in there and counteract oil pressure through the push rods and the rockers? which may be a good thing, IF oil levels in valve the covers are too high and do not drain fast enough into the case?

I am wondering this also.

Have Chris' (Tangerine) breather in the '73- case and heads vented thru it. No issues. Not cheap, but very nice.Click to view attachment

^^^ looks good! is there any baffle, foam or mesh in the catch can or empty?

On another note after reading a bit on breathers (including raby's link previouly posted) , I wonder if anyone has actually measured the air pressure in the valve covers?

There is information that under some circumstances, the valve cover cavity can get high levels of oil. Does anyone know if this was with or without a valve cover vent?

Foam in the inner chamber of the canister.

Air pressure inside the crankcase is no more than a couple inches of water column.
Ie, a small fraction of one psi.

Stock D-jet engines use a PCV valve. If that fitting on the oil tower box is used for a vent hose the guts need to be removed first.

Cool, thank you for the response

This is true but AFAIK only through '74. '75 2.0s had a larger open vent with no PCV that connected to a larger port on the air cleaner assembly. I Believe I have one of these air cleaner assemblies in my part stash somewhere. Not sure if the 2.0s ditched the head vents but I know the 1.8s did.

Funny watching all this discussion/testing come to the same conclusion that Porsche appears to have come to sometime in 74.

No pvc.

JamesM, as you mentioned it seems the factory itself had a few different venting configurations for their engines. However most if not all of those venting configurations were for emissions purposes.
Whereas many of the venting methods being discussed here are primarily for performance and engine longevity. Different goals will reach different conclusions, hence the discussions.