[ignaro]

I have these big fabricated valve covers without breather holes. Rather than drill a big traditional hole right in the middle, I'm trying to find a cleaner, invisible install.

Can I just drill little holes in the back of the valve cover and fabricate a little baffle inside to block oil from the holes? Is more really needed?

I thought I'd put a screw-in oil fill on the back of the valve cover, there are a lot of nice little options for that. I'll have a PCV in the Butler valley pan.

[Steve C.]

Might be of interest.....

I've seen breathers mounted on the side of a valve cover.

https://www.speedwaymotors.com/Speed...ther,8948.html


https://www.ebay.com/itm/Valve-Cover...-/222006518053

Many similar products out there.


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[ignaro]

Thanks-- that's the kind of oil fill cap I have in mind.

In looking for the smallest possible breathers, I found these -https://www.jegs.com/i/JEGS/555/50128/10002/-1 - but couldn't find anyone who had used them. Then I thought-- why not just drill holes and baffle internally against the occasional oil splash? Seems to me the breathers are all overbuilt for the task (which usually means I'm wrong!)

[ignaro]

-- or these VW ones that go to a hose. Could I leave the hose off? Am I just wrong about how much oil leakage a more open breather would allow? https://www.jbugs.com/product/9164.h...BoCsp0QAvD_BwE

[Formulas]

The thing is when and if enough pressure / volume of combustion pressures go past the rings they need a way out of the block and fast

Remember at full throttle the pcv valve does near nothing in terms of evacuation because vacuum is next to nothing it's at this time you need a adequate ventilation through a breather as air will exit the block in this manner then you close throttle vacuum comes up and air gets sucked in through the breather via the PCV valve

Myself if using a PVC valve I would want a breather in each valve cover or at a minimum just one side like stock

["QUICK-SILVER"]

Use a vented/breather cap for oil fill. Will only need one hole in one valve cover. (Like Factory)

Got to have a filter in the vented cap to keep dust, dirt, bugs, etc. out.

Clay

[ignaro]

Originally Posted by Formulas

The thing is when and if enough pressure / volume of combustion pressures go past the rings they need a way out of the block and fast

Thanks!-- agreed!
What kind of volume of gas is escaping at full throttle? I thought it was just a little burp, in which case a tiny 1/4" hole on each valve cover would be enough.

I found this video of clear lexan valve covers, showing how little oil is moving around in the rocker area, at least on a big block mopar. https://www.youtube.com/watch?v=W7w1y3OxDl4

[Steve C.]

During a dyno session I've had the pressure build up enough to push out the dipstick ! Subject to debate, having both valve covers vented is good.

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[Steve C.]

Just a tid bit for interest. As the norm information provided in this post does not represent any endorsement and is offered for general interest only....

Venting to Cure Crankshaft Pressure

https://www.hotrod.com/articles/vent...haft-pressure/

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[Sirrotica]

No formula, and each engine is different because of how it is initially built, the current condition of the rings, and cylinder walls, compression ratio, fuel being used, and how much throttle opening and RPM range the engine is seeing.

For an average engine 1/4 inch hole is not going to get the job done, when engineers used road draft tubes they were a minimum size of 1 inch. That's about 16 times the area of your proposed 1/4 inch opening. This is on a low RPM daily driver, doubtful you're going to get away with something 1/16 th the size that engineers designed even with daily driver usage. Even adding in the usage of a PCV vacuum system with 3/8 inch hose you're still short about the volume needed to vent crankcase vapor to the atmosphere.

In my 428 CU. IN. race car I had 2, 1 1/4 inch breathers to run 6000 RPM in an engine with good ring seal. Don't forget the breather not only vents blowby you have 8 pistons displacing 428 cubic inches varying the crankcase volume each revolution of the engine. The direction of air flow through the breather system can be flowing in either direction depending upon the conditions the engine is operating under.

My take is that you're woefully undersized in anything under 1 inch in a daily driver................ The 1 inch diameter equals out to roughly .8 square inches, the 1/4 inch equals out to roughly .05 square inches.

[ignaro]

Originally Posted by Sirrotica

My take is that you're woefully undersized in anything under 1 inch in a daily driver................

Thanks! Sounds like a lot more air is passing through than I had thought. I had attributed the 1" hole originally put in to needing to add oil. The valve cover breathers I saw for sale looked quite restritcive, which is why I thought a few small holes would do the trick.

[PontiacJim1959]

As noted, the internal pressures can often cause the dipstick to pop up, cause valve cover gasket leaks, and even rear main seal leaks. Those who go aftermarket with no provision for a breather, or those who eliminate the PCV system usually have oiling problems at some point and simply adding the breather and hooking up the PCV valve will cure the problem. If doable, a breather in each valve cover is best.

The choice of breather just depends on your build and what style you want to go with. A 1/4" hole won't work. You have to be careful as to where you locate the breather and whether you have a baffle to keep oil off it or not. Rocker arms throw/splash a lot of oil and then internal pressures can kick in as they vent out the breather.

I went with aftermarket finned valve covers on my build and am adding a set of Moon brand breathers to each side. They have a mesh in each breather. I am thinking that locating them on the top side of the valve cover should help. If I have any issues with oil, then I will come up with some kind of baffle.

[Sirrotica]

Just to prove the point that the crankcase gases be can be either entering, or leaving through the breathers. When I raced dirt track cars, we used to roll white cotton sweat socks over the whole breather stack. The socks would get changed usually weekly because of the dust buildup on the outer layer.

When there was negative crankcase pressure the dust would accumulate on the socks. You really don't want any fine dust entering through the breather elements under negative crankcase pressure. The dust is going to end up in the oil. Rapid wear will show up with dust entering the crankcase very quickly.

Running a dirt track car weekly gives you a rapid education on a lot of severe scenarios that can be of help with any application, be it daily driver or street/strip cars. You end up using your experience to solve the problems associated with a severe environment.

FWIW, most oval track cars have at least 2 breathers at least 1 inch in diameter minimum.

These are typical valve covers used on a dirt track engine, the one with the stacks goes on the left side of the engine using centrifugal force to pull oil down the tubes. Notice the tube size and area they use to vent gases, they work very well.

[Steve C.]

Brodix breather kits on each valve cover and a valve cover oil filler cap up front on the drivers side.......

https://www.hotrod.com/articles/0712...ImageId=243981


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[Formulajones]

Originally Posted by ignaro

-- or these VW ones that go to a hose. Could I leave the hose off? Am I just wrong about how much oil leakage a more open breather would allow? https://www.jbugs.com/product/9164.h...BoCsp0QAvD_BwE

I use those on our air cooled VW. Thing is, they are designed to attached a hose. I have both hoses going up to a centralized breather compartment that is filtered. Basically acts like putting a breather cap on a valve cover accept it's up much higher to keep water out, in case we go splashing through a deep creek or wash.

You won't be able to just run those open on a valve cover. The oil mess it would make running them open would be pretty extreme for starters. You really want some sort of filtered breather on your valve covers. At least one valve cover, that would be sufficient and what the factory would have had.

[ignaro]

Thanks everybody for your responses, I'm convinced I need a filtered, full-size breather. I'm going to wait until I have the engine finished before deciding on what exactly to run.

@Steve C-- thanks for that link, it's very similar to my build, I'm just trying to keep the engine compartment as trim and tidy as I can.

[NeighborsComplaint]

4 of these + some hose.

Drill and mount to back of valve covers and underside of air cleaner.

Hidden, neat and clean w. no misting all over the valve covers.

[chuckies76ta]

Originally Posted by ignaro

I have these big fabricated valve covers without breather holes. Rather than drill a big traditional hole right in the middle, I'm trying to find a cleaner, invisible install.

Can I just drill little holes in the back of the valve cover and fabricate a little baffle inside to block oil from the holes? Is more really needed?

I thought I'd put a screw-in oil fill on the back of the valve cover, there are a lot of nice little options for that. I'll have a PCV in the Butler valley pan.

I've always assumed to stay away from the back of the valve covers with any type of breather as the oil is forced to the back on hard acceleration.

[Formulajones]

Originally Posted by chuckies76ta

I've always assumed to stay away from the back of the valve covers with any type of breather as the oil is forced to the back on hard acceleration.

Yup,

Really the best place is in the center of the cover and up on the higher part of the cover.

Lots of tasteful ways of doing that if you're worried about making it aesthetically appealing

[TCSGTO]

Originally Posted by ignaro

I thought I'd put a screw-in oil fill on the back of the valve cover, there are a lot of nice little options for that. I'll have a PCV in the Butler valley pan.

Unless it’s one of the repro valley pans I wouldn’t try running a PCV in it. The sheet metal pans will suck massive amounts of oil thru a PCV valve.