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Author Topic: Appropriate size breather box  (Read 14856 times)
Eric Justus
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« on: November 18, 2008, 06:38:46 AM »

Id like to hear from "around the globe" some trials and tribulations with breather box capacity vs. motor combo/size. I am blue printing our new motor and I always like to hear some stories on what has worked the best and worst. I have used a few different set ups, but its always nice to hear from the creative minds of the fellow vw community.  Wink Cheesy
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« Reply #1 on: November 18, 2008, 15:01:14 PM »

http://www.thesamba.com/vw/classifieds/detail.php?id=462643
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« Reply #2 on: November 18, 2008, 18:48:23 PM »

I use this one, very nice. A bit too mirror-like finish for me, but nothing 240 grit paper couldn´t fix.
http://www.csp-shop.de/shop2/frame_nachladen.php?func=det&wkid=69947714290&rub1=Engine&rub2=Breather+Boxes&artnr=13816a&pn=0

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« Reply #3 on: November 19, 2008, 19:52:37 PM »

another

http://www.thesamba.com/vw/classifieds/detail.php?id=693462
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« Reply #4 on: November 20, 2008, 01:06:26 AM »

This picture is my favorite breather box picture.... Straight to the point... venting where the excess pressure really is...
Would be interesting to know if Håkan is venting the valve covers too?
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Neil Davies
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« Reply #5 on: November 21, 2008, 11:46:28 AM »

I found that the routing of breather hoses was very important. My little 1600 revved to around 6000rpm and had breather pipes from the rocker covers and the oil filler and fuel pump block offs. The various pipes were joined by T-pieces into one line and then went to a breather box made from an old fire extinguisher (nice little aluminium bottle between the decklid hinges!). Used that same arrangement with my 2180 and got a weep from one rocker cover, then with the 2276 it got worse. Both revved to about 7400rpm. We worked out that the one rocker cover was becoming pressurised by the route of the breathers at high RPM - made another box with four "in"s and one "out" with a little K&N filter.
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Eric Justus
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« Reply #6 on: November 21, 2008, 16:29:25 PM »

Has anyone truly found out the functionability and reasoniing behinding venting the valve covers to the sump? Other than draining oil due to gravity, I dont see how this would be a huge beneft if the covers are already venting to a breather box? Or am I am I completely wrong and someone has a smart answer for me? Huh Tongue Wink
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« Reply #7 on: November 21, 2008, 18:30:48 PM »

     Well from my understanding the benefit of drain back lines to the sump is to keep supply up. Depending on what heads and covers you use there might be as much as 2 or 3 qts. in the valve covers alone. There is a video by Muffler Mike somewhere showing a windowed valve cover filling up at around 6000rpm. so when you factor in your oil lines,filter, oil passages, push rod tubes, valve covers, probably even breather lines and possibly even breather box, thats alot of oil not in the sump at high rpm. Mike Lawless did a how to and a very good explanation story in a past Hot V.W.'s issue but I don't remember which one.

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« Reply #8 on: November 22, 2008, 00:19:07 AM »

Has anyone truly found out the functionability and reasoniing behinding venting the valve covers to the sump? Other than draining oil due to gravity, I dont see how this would be a huge beneft if the covers are already venting to a breather box? Or am I am I completely wrong and someone has a smart answer for me? Huh Tongue Wink

I have a hard time recognizing the benefit..., there are already four drain back tubes into the engine case, one more makes a huge difference...?
Muffler Mikes video is interesting... it shows that the oil doesn't want to leave the valve covers... could it be related to pressure differences?
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« Reply #9 on: November 22, 2008, 01:54:26 AM »

Good points here guys. I have a 1914 making 140hp and all I have for a venting system is the standard hoses to the valve covers and one hose to the bung on stock oil filler. My breather box is a cheapo aluminum box. It can hold 1/4qts. max I would say. I regularly zing my engine to 6k+ rpms and have never experienced any blowby, misting on engine, etc. I do not have a sand seal behind my berg pulley.
 
A race engine with higher compression that makes more horsepower and torque probably changes the equation significantly. Why is this though? Is there one aspect that changes everything or is it an increase in demand on the entire system?
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« Reply #10 on: November 22, 2008, 02:34:32 AM »

Has anyone truly found out the functionability and reasoniing behinding venting the valve covers to the sump? Other than draining oil due to gravity, I dont see how this would be a huge beneft if the covers are already venting to a breather box? Or am I am I completely wrong and someone has a smart answer for me? Huh Tongue Wink

I have a hard time recognizing the benefit..., there are already four drain back tubes into the engine case, one more makes a huge difference...?
Muffler Mikes video is interesting... it shows that the oil doesn't want to leave the valve covers... could it be related to pressure differences?
  by the four drain back lines do you mean the pushrod tubes? not sure there, if so they would theoretically be full of oil if the valve covers are to. I'm not saying I'm an advocate of this Eric just brought it up and I'm trying to explain what I understand of it. Whichever HOT V.W.'s issue it is that has the story from MIke Lawless is much more informitive as to the theories and or facts of this modificaton. I don't do this nor does the S/G car I crew chief for but I know alot of people do run them.  I think the pressures inside the case has a great deal with keeping the oil in the covers. In thinking about it myself I presume there is possibility of the pump creating a vaccum drawing the oil from the drain back lines. Also I've seen guys run 2 drain backs per head.
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« Reply #11 on: November 22, 2008, 14:24:11 PM »

  by the four drain back lines do you mean the pushrod tubes?
Yes I do.
if so they would theoretically be full of oil if the valve covers are to.
If those four are full of oil, the new "lower" one will be filled to... and the same pressure difference would be acting on this new one, even if it was below the oil "level"
I'm not saying I'm an advocate of this Eric just brought it up and I'm trying to explain what I understand of it. Whichever HOT V.W.'s issue it is that has the story from MIke Lawless is much more informitive as to the theories and or facts of this modificaton.
I understand where your comming from, and I must get hold of this story...
I think the pressures inside the case has a great deal with keeping the oil in the covers.
Yes I do to, Muffler Mikes theory says that this filling comes from the rotation of the crank and obviously from lubing the rockers... I believe in this to but I think the reason for the oil not returning is that we vent the covers... why would the oil leave low pressure conditions to go back in to the high pressure area? If gravity is not enough...

Actually, setting up a engine in a Spintron machine could give an answer to this pretty easy, if you had a window in the rocker cover. The spintron can spin the engine at 7000 without it actually running (electric motor). In this case the blow by pressure would not be present in the case... would the oil run back in to the case then??

In thinking about it myself I presume there is possibility of the pump creating a vaccum drawing the oil from the drain back lines. Also I've seen guys run 2 drain backs per head.
The best solution to all this is a full on dry sump... but I dont want to go there yet... Smiley
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« Reply #12 on: November 22, 2008, 15:11:06 PM »

actually the push rod tubes would be above the sump and pickup the drain backs go down to the sump "behind" the oil being sucked by the pump hence a possible draw by the pump. For what it's worth this is not my area of expertise and the mag write up is where the info is.
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« Reply #13 on: November 24, 2008, 00:50:11 AM »

I've tried a lot of different combinations to keep oil where it belongs, and the HVWs article that Jason so kindly mentioned is close to being the culmination of that. A race motor, because of the oil being pumped into and slung off of the crankshaft at high RPM creates a big vortex of oil that is being slammed into the 3-4 rocker box thru the pushrod tubes that are supposed to allow drainback. This is what a big drain line running to the sump below the windage helps...but ONLY if the top of the case is vented and not the valve covers. If you vent the valve covers, don't bother with the drain lines because the oil will take the path of least resistance....up the breather line and into the breather box and NOT into the sump. If the top of the case is vented, the case becomes a lower pressure area than the VCs and the oil will be forced under pressure back to the sump....where it belongs. Currently I have a single #10 breather line from the oil fill tower which is baffled. The line goes into the bottom of a baffled 2 quart tank. There are no vents on the VCs. I have scavenge lines going from the bottom of the head to the small stage of an autocraft stage a half oil pump.

Lots of opinions out there about what works. I can tell you my motor now stays bone dry on the outside and my bearings are always nearly perfect on teardown after 60 or more runs at 8500rpm with a 14-1 CR because the oil stays where it belongs. So listen to the opinions, make your decision and observe the results. You'll eventually find something that works for you.
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« Reply #14 on: November 24, 2008, 02:34:29 AM »

great info Mike thanks.
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Taylor
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« Reply #15 on: November 24, 2008, 08:22:32 AM »

im still not sure I buy the wave of oil off the crank shaft.
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« Reply #16 on: November 24, 2008, 15:40:54 PM »

OK Taylor. That's good. Since I've known you for a quite a few years, I know that you are much smarter and much more motivated than many. Do your own research. One place to start is to look into some V8 style oil pans the NHRA Comp and Super Stock guys use. They have built in scrapers and a kick-out on the left side to redirect the oil back into the sump.

Doing your own research and coming up with your own answers is a good thing. Hopefully by doing so you might come up with something we haven't tried, which after all is the point of us all discussing this.
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« Reply #17 on: November 24, 2008, 15:43:33 PM »

If you vent the valve covers, don't bother with the drain lines because the oil will take the path of least resistance....up the breather line and into the breather box and NOT into the sump.

You are talking my language here now, this is exactly what my thoughts have circled around... pressure differences. When you vent in the VC much of the blow by pulses will travel up the push rod tubes... fat chance any oil drains back that way... would be like pissing against the wind  Shocked
Next spring my venting will be done in the Generator stand... only!

Any pics of your solution mr. Lawless?
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Eric Justus
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« Reply #18 on: November 24, 2008, 16:17:58 PM »

lots of good stuff here  Cheesy
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« Reply #19 on: November 24, 2008, 16:56:27 PM »

If you vent the valve covers, don't bother with the drain lines because the oil will take the path of least resistance....up the breather line and into the breather box and NOT into the sump.

You are talking my language here now, this is exactly what my thoughts have circled around... pressure differences. When you vent in the VC much of the blow by pulses will travel up the push rod tubes... fat chance any oil drains back that way... would be like pissing against the wind  Shocked
Next spring my venting will be done in the Generator stand... only!

Any pics of your solution mr. Lawless?

Here's a shot of the external arrangement as of now at the top of the page. Scroll to the bottom and you can see from the earlier shot that the fill tower has grown to contain some baffling and the single hose to the breather box is all there is. Inquiring mind may want to know where the hose from the top of the breather tank goes....

http://home.comcast.net/~mlawless29/hardware.html
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« Reply #20 on: November 24, 2008, 18:29:43 PM »

im still not sure I buy the wave of oil off the crank shaft.

I do!!

Next time I see you, you should have a drive in my car. It still sports the original engine (closing in on 122k miles), with a couple performance mods. You can take that car around any left hand corner as fast as you please, and the oil pressure wont hardly budge. Do the same on a right hander, and the oil pressure plummets!! Why? Because the crankshaft is fighting the oil "slosh" on left turns, and doing the exact opposite on right handers.
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« Reply #21 on: November 25, 2008, 18:42:14 PM »

Definitely agree with Mike Lawless and others that oil is being flung off the crank and
up the pushrod tubes into left cylinder head rocker chamber.

A lot of racers consider it normal to empty their puke tank after each pass. In some
cases this will be due to poor ring seal and excessive blowby but case windage and/or
inadequate breather design are certainly an issue.

Few years ago Engine Machine Service ran an engine on their dyno with a windowed rocker
cover to see what's happening at high rpm. Muffler Mike posted the video on his site. You
can clearly see the rocker cover fill with oil. You don't see the same effect on the 1-2
head. I've seen exactly the same thing here.

The longer the stroke, the higher the rpm, the greater the problem.
If you're sat on the outside edge of a crank counterweight and spinning at 8000rpm, 88mm
stroke crank has you covering more distance in the same time than you would on a 69mm
i.e.  you're travelling faster

I've seen internal case pics of cranks at high speed. Engine oil is literally wrapped and
twisted around the crank like a thick rope.

In the likes of Nascar, Pro Stock and other high end engine categories the engine builder
will go to great lengths to reduce the amount of oil that is flung around inside the
block by incorporating baffles, screens, scrapers, custom shaped oil pans, trap doors etc
etc..... i.e. whatever they can do to take oil off and away from the crank.

Dry sumping the engine is the ultimate way to go but a well designed dry sump system will
still include various tricks and modifications to divert and control oil travel.

In a wet sump motor most important thing is to ensure there's an adequate supply of oil
at the oil pickup pipe. The aim should be to collect and divert all oil coming off the
crank (having lubed the mains and big ends) away from rotating parts and straight back to
the sump.

I'm not sure it's even possible to squeeze in a set of oil scrapers like the V8 guys use
because of the upside down crank/cam orientation used in the VW. I've looked for a way
but haven't found one yet!

Popular approach nowadays, as mentioned in this thread, is to accept the fact oil gets
thrown into the left head and alleviate the problem by adding a drainback facility. This
obviously helps reduce the amount of oil hanging around in places it serves no purpose.
Some even block the oil holes in the 3-4 head pushrods to further reduce the amount of
oil going to that side of the motor.

When a crank beats and whips up hot oil at 8000rpm it makes a nice job of turning it into
froth... you're trying to lubricate your motor with fizzy oil.

Ever seen race engine's rod bearings with an alligator skin appearance? I believe that's
cavitation erosion - inadequate lubrication caused by pumping aerated oil through the
system. You want a ready supply of non-aerated oil available at the pickup at all times
i.e you don't want the crank to whisk/beat the shit out of the oil!
Harder to cool aerated oil too!

I've been looking at this problem for a while and have gradually been incorporating a few
internal case mods with a view to reducing the problem - especially for high rpm, long
stroke engines.

Part of the problem is the basic flat four engine design.... the boxer engine is
inherently well balanced.... for each piston/rod movement, there is an equal and opposite
deal happening on the other side. Now take a look at the case design. It effectively
seals off one case half from the other, with 1 & 3 operating in one half and 2 & 4 in the
other. When 1 & 3 are heading down to BDC, 2 & 4 are on their way up.

I recall reading somewhere this is one of the reasons Ferrari dropped their boxer race
engine... the design had advantages in terms of balance but internal windage was always
an issue. Switching to a V config was also more compact so windage wasn't the only factor
but it's significant they cited it as a problem.

F1 engines and other mega buck stuff deliberately compartmentalise pairs of opposing cylinders.
Each compartment is individually scavenged of oil by its own dry sump scavenge section.
In V configuration the paired cylinders don't have the disadvantage of operating in boxer
mode.

Back to the VW.... when a pair of pistons (say 1 & 3) are on their way down they have to
displace air somewhere. At the same time 2 & 4 are on the way up, making room for that
displaced air. So you have a continual high speed exchange of air taking place between
the front and back halves of the case. The path of least resistance (most space for the
air to make its move) is down by the cam. At high engine speeds I believe this super
rapid and turbulent air exchange is creating havoc with oil return to the sump.
Amount of air displacement increases with bore and stroke.

My mods are aimed at equalizing pressure between the front and rear case halves in
an attempt to reduce the storm to a breeze.

Also thought about trying the rocker drain idea but figured it might be better to
minimise the amount of oil getting up there in the first place. Have to be careful not to
limit drainback through the pushrod tubes. Sort of like a one way system.

First engine I tried some of this stuff was an 88mm stroke race engine - an ideal candidate to experiment
on. Normally an engine of this type will puke some oil out the rocker cover breathers at
high speed, especially on the 3-4 head. For the dyno tests I fitted a pair of stock
rocker covers with 1/2" ID breather hose connected. Both hoses were routed into separate
drain pans.

First wide open throttle pull I was hoping the mods would result in a reduction in the
amount of oil out the 3-4 rocker breather compared to what I've seen before. The pan was
bone dry! I used the same breather setup for the whole test session, including runs on
nitrous. The drain pans stayed dry throughout.

Testing on the dyno can't replicate oil movement that takes place due to launch,
acceleration, braking etc so was keen to hear feedback from the owner's experience at the
track.... he reports very minimal amount of oil deposited in the catch tank.

This is a work in progress so no detailed pics of the mods yet but it all starts to make
sense if you study the internal layout of the case, picture what's going on re piston
movement, figure how you can keep oil away from the crank and cam etc etc

Mentioned blowby/ring seal at the start.... this is improved by equalizing internal case
pressure and reducing windage. Reduce pressure below the piston by say 1 psi, that's 1
psi less the downward travelling piston has to overcome on the combustion stroke i.e.
better ring seal and more power at the flywheel

« Last Edit: November 25, 2008, 18:52:35 PM by John Maher » Logged

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« Reply #22 on: November 25, 2008, 19:58:21 PM »

Fantastic stuff here John, can't wait to see your pictures as I am sure they will be very helpful to others. Cool Matt
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« Reply #23 on: November 25, 2008, 20:46:34 PM »

so, if i run a line off the oil fill tube and not VC vents i should be okay under 6k rpm mike?  i like that idea alot!!! 
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« Reply #24 on: November 25, 2008, 21:13:06 PM »

Inquiring mind may want to know where the hose from the top of the breather tank goes....

Is there where the "and a half" comes in? Smiley
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« Reply #25 on: November 25, 2008, 23:56:12 PM »

So to add to this thread even more, I haven’t read much on capacity of the breather box itself. What is the recommended capacity ratio per engine specifications? For the motor I am currently working on right now, I am leaning towards a 2 quart breather, but I’d also like to read some insight on the appropriate capacity of the breather for the application it is being used for. Anyone? Wink Grin
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« Reply #26 on: November 26, 2008, 02:05:48 AM »

Take a look @ where the breather comes off of on a 911 (any of them) or even one of the old 4 cam 4 cylinders.
The pistons coming down from TDC oppose one another in a VW, so yes you're asking these two comlumns of air under those 94mm piston undersides (parachute shaped!) to ram into one another, and like JM said, with longer stroke it gets worse...here is another reason.
My friend found the aftermarket alum cases were even worse when it came to windage. Reason he found was webbing was so heavy and bulky in case that it was creating air dams! On mag VW cases, I round the main webbings off with sanding cartridges, to help present an easier path to those columns of air. Porsche did this in the 901/20 motors in 1965 and found 10hp just by this mod alone.
It isn't just ring seal that causes the froth-storm... though that has A LOT to do with it. Before I re-did the race motor at my old job (not sure who built it previous to me) it had horrible windage problems, and became the butt of many oil down jokes. Upon taking it down, I found the compression rings were obviously shot, and ring gap was wide open, and you could see where corners of 1st and 2nd rings were rounded off. New rings, manicured webs in VW case and attention to oil level sure made a world of difference, as the car now left the track dry for the next guy.
I run a small, maybe .5 liter box my friend fabbed for me and stock VW 12mm hose from stock filler and covers. I regularly run my car up to 7000 (street car) and it isn't puking itself all over.
I think ideally, fabbing a take off directly off case (on race motor where no shroud is used) would be ultimate in solving the two columns of air fighting each other
see ya guys
Jim
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« Reply #27 on: November 26, 2008, 10:02:25 AM »

I think ideally, fabbing a take off directly off case (on race motor where no shroud is used) would be ultimate in solving the two columns of air fighting each other

If one consider the path the air have to navigate to get to the timing gear "chamber", and then up the generator stand it makes sense to vent in the roof abow 2&4 AND 1&3... but I'm not so sure its smart to make holes there in a mag case.
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« Reply #28 on: November 26, 2008, 15:53:27 PM »

I think ideally, fabbing a take off directly off case (on race motor where no shroud is used) would be ultimate in solving the two columns of air fighting each other

If one consider the path the air have to navigate to get to the timing gear "chamber", and then up the generator stand it makes sense to vent in the roof abow 2&4 AND 1&3... but I'm not so sure its smart to make holes there in a mag case.

And in a typ 4 case??

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« Reply #29 on: November 26, 2008, 15:59:37 PM »

There is definitely more of an internal venting problem with the aluminum cases. Most builders have found it necessary to do quite a bit of deburring as Mr Ratto pointed out. The port going thru to the timing box can be almost completely closed off with casting flash and the spigot windows need work too. For the most part, that is all one can do in a practical sense. Anything that can be done to enhance the return flow back to the sump is a good thing to do.

To answer the breather box size question... on a race car, while a small size would might work in most cases, the ruling actually calls for a quart minimum. Common courtesy dictates more. It's better to err on the side of preventing oil spillage IMO, and keeping our fellow racers safe from driving through anything that could easily be prevented.
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