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Sat Nov 30, 2024 10:57 pm

Totally get venting crankcase. No problem there. What I don’t get is valve cover venting. Every time a piston goes up (increasing pressure) on a given head, the other one on that side goes down (decreasing pressure). If you are venting the crankcase already, the neutral valve cover contents is doing nothing. I am venting through the old fuel pump location and don’t understand the engineering of venting valve covers beyond the crankcase venting. Can somebody sprain the engineering rational behind this, please?

Sat Nov 30, 2024 11:54 pm

It's pointless. Crankcase pressure originates in the crankcase. The pushrod tubes are full of oil and pushrods, so very little pressure is able to get vented from the covers. All they are good at doing is allowing oil to get pumped out of the rocker box on the 1/2 side and out into the breather box. If you need to vent the crankcase and your valve covers to control oil leaks out the pulley hole, you gave piston ring problems and you're bandaiding the problem.

I only run lines from my oil fill and fuel pump blockoff to a 3qrt CSP breather box on my racecar and just run a CB breather tower on my street engines.

Sun Dec 01, 2024 4:45 am

Now, what if you are running a blower?

Sun Dec 01, 2024 8:13 am

I have a different perspective. Venting the valve covers does help vent the crankcase. It also allows oil to return to the sump much faster. On my 7000 RPM race engine I have no issues with oil being pushed out the VC vents. Some folks run stock fuel pumps and can not use that location for a vent.

Sun Dec 01, 2024 9:09 am

Nice to see a “new” discussion, this will be fun.
I agree with Dave on this one, if definitely allows the oil to drain better, also lets the engine breathe and helps keep the covers from leaking.
You dont think crank case pulsation affects the pushrod tubes?
Think the covers are neutral, then why do valve cover gaskets get sucked in?
Why do majority of engines have a breather on valve covers but it’s not necessary for a flat 4 vw? If anything it should be more necessary for us as our valve covers area fills with so much oil.
I know other guys will have really cool scientific explanations of the pulsation in the case and ive heard that theres actually a oil vapor “cloud” that forms in the case from it, but i dont know about all that, sounds plausible though. And i dont think a single 3/4” or 1/2” line is enough to help control that.

Ever since my first boosted vw ive vented the covers and the fill tube, typically to a multi port breather box of some sort, on almost every engine ive built.

Sun Dec 01, 2024 9:17 am

Eastbay851 wrote: Now, what if you are running a blower?

My race engine is turbo'd. I race at Bonneville so my engine sees 5000-7500 for 2 and a quarter miles

Sun Dec 01, 2024 10:12 am

My experience is that with unvented valve covers, I suddenly was seeing more oil mist/ residue at the oil filler breather and rear pulley. No clue why exactly, just my experience, and I tried several things to see what helped or didn't.
Right now I have both valve cover vents connected to the lower back of the generator stand, and I have a pretty clean engine. My thought is that when one head/ rocker box is full of oil, the vent allows an air path to help the oil drain back faster. Without an air inlet, the head could be slower to drain.. in any even I'm not 100% sure why this works for me but it does without the need for extra breather boxes and miles of hose. And, FWIW, my pushrods are drilled to spray oil on the springs, and full hoover mods, so there is considerably more oil in the heads.
SD

Sun Dec 01, 2024 10:13 am

I’m not in favor of “venting” the valve covers. To me, it’s moving the gasses the wrong direction.

This is very evident when comparing used heads from PCV equipped engines (Type 3 & 4 with Djet), and those without. The PCV system had the fresh air inlets in the rocker covers. Clean filtered air enters the rockers, pulled through the pushrod tubes into the case, then out the top of the case into the intake. The PCV engines always have very clean rocker boxes with less buildup. Case internals are often cleaner too, with less pitting in the sump. The engines with the most crap in the heads are usually ones where people added vents to the heads. Just my observations. :wink:

In my opinion, it takes a very special engine to actually require more venting volume capacity than was available stock. Unless it is a very high rpm big bore engine, it shouldn’t need more than a 1/2” hose. All those sub 2.0 engines that people claim need the rocker boxes vented probably just have crap ring sealing and need to be rebuilt.

Sun Dec 01, 2024 10:52 am

It seems logical that larger displacement and higher rpms create more turbulence. Also, do counterweights increase that as opposed to non counterweights?

Sun Dec 01, 2024 11:31 am

Why? why not. That's about it.
You can have a good breather system or a bad one, venting the valve covers or not venting them.

Strokers usually have an increase in pulsation from the lower rod ratio.

Sun Dec 01, 2024 11:35 am

Vanapplebomb wrote: I’m not in favor of “venting” the valve covers. To me, it’s moving the gasses the wrong direction.

This is very evident when comparing used heads from PCV equipped engines (Type 3 & 4 with Djet), and those without. The PCV system had the fresh air inlets in the rocker covers. Clean filtered air enters the rockers, pulled through the pushrod tubes into the case, then out the top of the case into the intake. The PCV engines always have very clean rocker boxes with less buildup. Case internals are often cleaner too, with less pitting in the sump. The engines with the most crap in the heads are usually ones where people added vents to the heads. Just my observations. :wink:

In my opinion, it takes a very special engine to actually require more venting volume capacity than was available stock. Unless it is a very high rpm big bore engine, it shouldn’t need more than a 1/2” hose. All those sub 2.0 engines that people claim need the rocker boxes vented probably just have crap ring sealing and need to be rebuilt.

Beat me to it. The type 4 cars and 914's with the same engine and t9 some respects the type 3 cars with D-jet.....used vented rocker boxes.....but they vent INWARD pulling in filtered air from a special section of the air cleaner.....through a flame trap.....and through the PR tubes....through the case....out the top at the oul bagel as Vanapplebomb noted.

Very clean. Runs a little cooler in some climate. Ray

Sun Dec 01, 2024 12:25 pm

raygreenwood wrote: Vanapplebomb wrote: I’m not in favor of “venting” the valve covers. To me, it’s moving the gasses the wrong direction.

This is very evident when comparing used heads from PCV equipped engines (Type 3 & 4 with Djet), and those without. The PCV system had the fresh air inlets in the rocker covers. Clean filtered air enters the rockers, pulled through the pushrod tubes into the case, then out the top of the case into the intake. The PCV engines always have very clean rocker boxes with less buildup. Case internals are often cleaner too, with less pitting in the sump. The engines with the most crap in the heads are usually ones where people added vents to the heads. Just my observations. :wink:

In my opinion, it takes a very special engine to actually require more venting volume capacity than was available stock. Unless it is a very high rpm big bore engine, it shouldn’t need more than a 1/2” hose. All those sub 2.0 engines that people claim need the rocker boxes vented probably just have crap ring sealing and need to be rebuilt.

Beat me to it. The type 4 cars and 914's with the same engine and t9 some respects the type 3 cars with D-jet.....used vented rocker boxes.....but they vent INWARD pulling in filtered air from a special section of the air cleaner.....through a flame trap.....and through the PR tubes....through the case....out the top at the oul bagel as Vanapplebomb noted.

Very clean. Runs a little cooler in some climate. Ray

Really sounds like a contradictive statement, yall are saying your not in favor of vented covers yet the mentioned engines with vented covers are all around cleaner. Only real difference is the design in flow and manufacturer vs. an individual’s installation. Maybe the difference in cleanliness is due more to the individual not running though good enough filtration, or the use of empi’s stubby little vent tubes that dont seal great & too short to keep a hose on? Or possibly the application of the engine, was the dirtier ones ran in offroad conditions vs the type4 you mentioned as cleaner strictly road use?
Not trying to be critical just an observation and idea about it

Sun Dec 01, 2024 2:45 pm

With less space in the case from stroker cranks via physical space, and via more stroke invading the area, the need for venting goes up. The worst time is when the rings have not seated and the case breather is working overtime.

Adding just a passenger side valve cover hose to the breather has been my "go to". I do 10AN for the most out of that one side.

If your able to survive without out adding a passenger side breather, thats great. However, i do not believe there is a downside, and letting the crank case breathe as good as possible could free up a horsepower or 2.

Sun Dec 01, 2024 2:58 pm

Or it will piss past the oil slinger.

Sun Dec 01, 2024 3:51 pm

Hey Jeff - Did you tig that An10 on there? There isnt much room to get in there for welding. Or is it welded on the inside?

Sun Dec 01, 2024 8:06 pm

Hey Chris, Tig would be nicer. I used a wire feed. Got around the slightly tight area between the bung and the gasket flange fine like that. Not ideal but gets it done. Steel 10AN welded to a steel valve cover is a decent way of doing it.

Much better then the Empi slip on bungs where people use breather hose aned a worm drive hose clamp that slips off and gives a james bond oil smoke down the street.

Sun Dec 01, 2024 8:11 pm

BFB wrote: raygreenwood wrote: Vanapplebomb wrote: I’m not in favor of “venting” the valve covers. To me, it’s moving the gasses the wrong direction.

This is very evident when comparing used heads from PCV equipped engines (Type 3 & 4 with Djet), and those without. The PCV system had the fresh air inlets in the rocker covers. Clean filtered air enters the rockers, pulled through the pushrod tubes into the case, then out the top of the case into the intake. The PCV engines always have very clean rocker boxes with less buildup. Case internals are often cleaner too, with less pitting in the sump. The engines with the most crap in the heads are usually ones where people added vents to the heads. Just my observations. :wink:

In my opinion, it takes a very special engine to actually require more venting volume capacity than was available stock. Unless it is a very high rpm big bore engine, it shouldn’t need more than a 1/2” hose. All those sub 2.0 engines that people claim need the rocker boxes vented probably just have crap ring sealing and need to be rebuilt.

Beat me to it. The type 4 cars and 914's with the same engine and t9 some respects the type 3 cars with D-jet.....used vented rocker boxes.....but they vent INWARD pulling in filtered air from a special section of the air cleaner.....through a flame trap.....and through the PR tubes....through the case....out the top at the oul bagel as Vanapplebomb noted.

Very clean. Runs a little cooler in some climate. Ray

Really sounds like a contradictive statement, yall are saying your not in favor of vented covers yet the mentioned engines with vented covers are all around cleaner. Only real difference is the design in flow.

It is the direction of flow and what is flowing that makes the difference. One method purges the case with fresh air. The other doesn’t. Hope that makes sense. 8)

Sun Dec 01, 2024 8:41 pm

Vanapplebomb wrote: BFB wrote: raygreenwood wrote: Vanapplebomb wrote: I’m not in favor of “venting” the valve covers. To me, it’s moving the gasses the wrong direction.

This is very evident when comparing used heads from PCV equipped engines (Type 3 & 4 with Djet), and those without. The PCV system had the fresh air inlets in the rocker covers. Clean filtered air enters the rockers, pulled through the pushrod tubes into the case, then out the top of the case into the intake. The PCV engines always have very clean rocker boxes with less buildup. Case internals are often cleaner too, with less pitting in the sump. The engines with the most crap in the heads are usually ones where people added vents to the heads. Just my observations. :wink:

In my opinion, it takes a very special engine to actually require more venting volume capacity than was available stock. Unless it is a very high rpm big bore engine, it shouldn’t need more than a 1/2” hose. All those sub 2.0 engines that people claim need the rocker boxes vented probably just have crap ring sealing and need to be rebuilt.

Beat me to it. The type 4 cars and 914's with the same engine and t9 some respects the type 3 cars with D-jet.....used vented rocker boxes.....but they vent INWARD pulling in filtered air from a special section of the air cleaner.....through a flame trap.....and through the PR tubes....through the case....out the top at the oul bagel as Vanapplebomb noted.

Very clean. Runs a little cooler in some climate. Ray

Really sounds like a contradictive statement, yall are saying your not in favor of vented covers yet the mentioned engines with vented covers are all around cleaner. Only real difference is the design in flow.

It is the direction of flow and what is flowing that makes the difference. One method purges the case with fresh air. The other doesn’t. Hope that makes sense. 8)

Yes...to add to this....it works on the type 4 engines (specifically with D-jet injection)....because this venting system uses full manifold vacuum through a 12mm hose sucking on the PCV valve at the oil vapor seperator chimney.

The PCV valve cracks open for 10ths or hundreths of a second dues to a combination of case pressure (if any) and vacuum from the manifold. It sucks any gases out of the case into the intake. A totally different concept from venting OUT of the valve covers into a low vacuum carburettor air cleaner and just hoping it sucks in any gases.

The type 4 case has a Z shaped baffel at the top of the case into the oil chimney that takes out a ton of oil vapor. The top of the oil chimney itself is an oil baffel...and a pretty good one.

Its a really good system but you need high vacuum to make it work in this direction...meaning sucking/pulling air THROUGH the rocker boxes and THROUGH the PR tubes and THROUGH the case and out the top.

You really can't do this well with carbs unless maybe you somehow plumb to the balance tube and then its a vacuum leak.

Its already a little bit of a vacuum problem with D-jet. Some of us fix this issue by going to a uniform 2-3mm orifice flowing full time instead of the factory PVC valve. We then adjust the fuel mixture accordingly (its a MAP based EFI system).

If you look at what gets baked onto the inside of the rocker boxes and case in a type 4 engine that does NOT use this system....you get an idea of exactly whatr its venting....so yes....it is effective. Ray

Sun Dec 01, 2024 9:25 pm

Venting the valve covers does help vent the crankcase. It also allows oil to return to the sump much faster.
That one defies logic! How does air flowing UP the pushrod tubes help the oil flow DOWN the pushrod tubes?

Sun Dec 01, 2024 11:28 pm

Why? I would think at some point someone copied the idea from the V8’S .
Then followed by a lot of monkey see monkey do .and here we are.
This topic is like asking what case sealer to use , everyone has either success
Or failure with the same product .
So why do some get away with more or less venting.It really comes down to ring seal , it’s already been mentioned. If you have it you will not have any issue and you can vent really where ever you want but if you have a crankcase pressure issue no matter what you do you will move oil .
Myself NO valve cover or fuel pump vent , just modified alt stand with a 1”id hose mounted to hi mounted moroso breathers.
If you have or think you have issues , measure it.
I use the fuel pump block off plate tapped with a barbed fitting attached to a vacuum/pressure sensor for you electronic data guys or s long piece of plastic vacuum hose mounted to a mechanical gauge up where you can see it .
Here is an old pic of what negative to positive crankcase pressure looks like when logged .again only an example . If you are N/A and using external breather setup you would hope for zero pressure across the complete run.
The line you’re looking at is the pink and in the boxes are the values .
Looks like I go from a negative to a positive value as soon as it hits 3rd gear.
You get the idea.