Head Breather, Reasons? Options

[Rhodes71/914]

It was recently brought to my attention that while I have my engine partially dis-assembled that I should put some breather lines into the heads.

Did a search, read some info but looking for more of course (aren't we all)

Just like to know the reason for doing this and also what different set ups ya have. Do ya like the valve cover option or drilling and tapping the boss in the head?

What size fittings are ya using.

TIA
Sean

[McMark]

Main reason: it stops the valve cover gaskets from getting sucked in and causing oil leakage.

Drilling the head bosses is preferred because if they're in the valve covers you have to unhook the tubing each time you check the valves and you also have a routing issue if you don't use the built in bosses.

Bosses are the winner! (IMG:http://www.914world.com/bbs2/html/emoticons/smilie_pokal.gif)

[SLITS]

Even with the best engine, combustion gasses pass by the rings, creating internal pressure in the crankcase. Combine this with a whirling crankshaft assembly, creating a small hurricane and the oil will froth and droplets are carried everywhere and WILL find a way out of the engine..whether it be the front or rear main seal, pushrod tube seals or valve cover gaskets or ??????

Secondly, in my dim memory, I remember something about high internal pressure being able to effect oil ring sealing too!

Solution....the old road draft tube, PCV valve, breather ports..even the drag racers used to try to pull negative pressure on the crankcase by intalling a one way valve in the exhaust system (at an angle) to have the rapid flow of exhaust gasses create a vaccum on the breather ports of an engine.

[Rhodes71/914]

Since this was brought up in another thread today I thought I would just add to this one already started.

Since I had to pull the heads from my engine I will be putting these breathers in.

My question is in regards to what to run the hoses to. Through my searched I see the carb guys use a little breather box, but found nothing for FI. Could you do this and just plug the hole in the plenum that the oil filler breather goes to?

What size are you using for the fitting in the head? Maybe the same size as the Oil filler breather line?

[SirAndy]

QUOTE (SLITS @ Dec 28 2004, 07:54 AM)

Even with the best engine, combustion gasses pass by the rings, creating internal pressure in the crankcase.

correct, but the heads actually *suck* at higer rpms. like mark said, the problem with the heads is that the gasket gets *sucked in* and then you got yourself a leak.

the head vents need to be routed together with the oil-filler neck vent.
on the stock setup they will all simply go to the air-cleaner.

on a carb setup, your best bet is installing a breather box ...

(IMG:http://www.914world.com/bbs2/html/emoticons/cool.gif) Andy

[SirAndy]

QUOTE (Rhodes71/914 @ Feb 20 2005, 12:45 PM)

Could you do this and just plug the hole in the plenum that the oil filler breather goes to?

only if you want your engine to explode ...


on a stock FI setup, run the vent hose from the oil-filler to the air cleaner. this is where your engine reliefs internal pressure. *do not plug* this!

second, run a hose from each head-vent, join them with a "Y" and them run that into the air-cleaner as well.

(IMG:http://www.914world.com/bbs2/html/emoticons/cool.gif) Andy

[MecGen]

Hi
Mine is set up with two hoses coming from the heads to a manifold that I made with copper tubing, painted black, also connected to the oil fill neck. no pcv. This all goes to a downdraft pipe, that passes thru the tin, and cut off in a angle 45, supposed to help with the flow. A breather box was my first option that I'd tryed, but for the life of me, I can't remember why it did not work, been running the downdraft for 12 years.
WBR
Joe

(IMG:http://www.914world.com/bbs2/html/emoticons/smash.gif)

[Rhodes71/914]

QUOTE (SirAndy @ Feb 20 2005, 12:59 PM)

on a stock FI setup, run the vent hose from the oil-filler to the air cleaner. this is where your engine reliefs internal pressure. *do not plug* this!

OK but the original routing of the oil filler breather is to the plenum on my 2.0.

So if I run that to the air filter I have a connection at the plenum that has no hose, so it should be plugged, correct (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

[SirAndy]

QUOTE (Rhodes71/914 @ Feb 20 2005, 01:05 PM)

So if I run that to the air filter I have a connection at the plenum that has no hose, so it should be plugged, correct (IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

nope, sorry, there are 2 different setups used on the 914.

on one setup the oil-filler neck vent goes to the air-filter, on the second setup it goes to the plenum.

if yours goes to the plenum, leave it there. that means you have a PCV in your oil-filler. on engines without PCV, that line goes to the air-filter.


soooo, all you need to do is to join the 2 head-vents with a Y and route them to one of the air-cleaner ports ...
(IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) Andy

[Rhodes71/914]

QUOTE (SirAndy @ Feb 20 2005, 01:09 PM)

if yours goes to the plenum, leave it there. that means you have a PCV in your oil-filler. on engines without PCV, that line goes to the air-filter.

Well here is my problem, the oil filler I have does not have a PCV Valve. Is it built into the filler, because I can't seem to find one that is separate. Do I have to have this or do I have another option?

[SirAndy]

QUOTE (Rhodes71/914 @ Feb 20 2005, 01:25 PM)

Well here is my problem, the oil filler I have does not have a PCV Valve. Is it built into the filler, because I can't seem to find one that is separate. Do I have to have this or do I have another option?

the PCV is inside the filler neck. if your filler doesn't have a PCV and you hook it up to the plenum, you'll hear a very loud noise as the vacuum of the plenum is sucking air out of the filler. that's a easy way to check if your filler has a PCV. if you hook it up to the plenum and it doesn't scream, you've got a PCV in there.
if it screams (no PCV), connect it to the air-filter instead and plug the plenum port ...

(IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) Andy

[Allan]

I was looking at some older threads regarding this and found this one that seems to add some confusion to this.

Vent

[SirAndy]

QUOTE (Headrage @ Feb 20 2005, 02:27 PM)

and found this one that seems to add some confusion to this.

yes, that was before i figured out how all this works ... (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

some engines didn't have the head-vents, like my old 1.8L
it only had the filler neck vent, with *no* PCV, and the breather hose went straight to the air-cleaner.
that setup worked just fine.

but since then, i have learned that the additional venting on the heads helps keeping your engine pressurized correctly ...

(IMG:http://www.914world.com/bbs2/html/emoticons/cool.gif) Andy

[MarkG]

QUOTE (SirAndy @ Feb 20 2005, 03:07 PM)

QUOTE (Headrage @ Feb 20 2005, 02:27 PM) and found this one that seems to add some confusion to this. yes, that was before i figured out how all this works ... (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif) some engines didn't have the head-vents, like my old 1.8L it only had the filler neck vent, with *no* PCV, and the breather hose went straight to the air-cleaner. that setup worked just fine. but since then, i have learned that the additional venting on the heads helps keeping your engine pressurized correctly ... (IMG:http://www.914world.com/bbs2/html/emoticons/cool.gif) Andy

So if I understand correctly, on my '76 2.0 D-jet, which has the oil filer/no PCV to air cleaner setup, I would still gain some bennefit by adding head vents? (will be removing air injection......).

[davep]

I think only the 1.8 engine did not have head vents. That engine, with stock FI, needed to be a sealed system, and would not run properly with leaking O-rings on the oil filler. All the air that 'can' enter the internals of the engine needs to have filtered air.

[Brando]

QUOTE (davep @ Feb 21 2005, 09:45 AM)

I think only the 1.8 engine did not have head vents. That engine, with stock FI, needed to be a sealed system, and would not run properly with leaking O-rings on the oil filler. All the air that 'can' enter the internals of the engine needs to have filtered air.

I believe you're right. with the AFM/AFC setup the whole crank is under vacuum right before the plenum on the intake. Any leaks and it will not run right due to unmetered air in the system.

You could go with head-breathers. Run them into a filter box, then to a 'T' fitting between the oil filler neck and the intake boot. Not sure what the benefit would be since the case is already under vacuum.