While pulling my carbs off I noticed that each head has an air vent. One was capped off, the other was open.

Where should these go and why are they needed? Will capping these contribute to oil leaks?

Here is a pic I found: http://www.914world.com/bbs2/uploads/blog-1...-1131214564.jpg

Thanks

You need the head vents to keep from building excessive crankcase pressure. The only 914 without head vents was the 1.8L with the L-Jet system. It uses a different system. If the vents are there, they make the engine run lean.

Hook them to a vent box mounted high up in the engine compartment.

Yea i figured that. There is no vent box on my car.

What connects to the vent box? Left head, right head and the vent next to the oil fill?

QUOTE (ClayPerrine @ Feb 6 2006, 08:11 AM)

You need the head vents to keep from building excessive crankcase pressure. The only 914 without head vents was the 1.8L with the L-Jet system. It uses a different system. If the vents are there, they make the engine run lean. Hook them to a vent box mounted high up in the engine compartment.

They appeared in 1973, possibly even in 1972. If your engine has a PCV valve in the oul filler box, you need them. If you have "enhanced" the induction system, say with big carbs, you need them. If in doubt, keep them. The factory thought they were important enough to add them, maybe your engineering department should consider it, too. The Cap'n

QUOTE (yarin @ Feb 6 2006, 08:28 AM)

Yea i figured that. There is no vent box on my car. What connects to the vent box? Left head, right head and the vent next to the oil fill?

Yes, all three vents can hook up to a box. I left the PCV on the oil filler connection. mine is made by EMPI. I think CBperformance sells them for the bug crowd.
Works for me but YMMV

engines that can't breathe don't have all their power freed up AND they leak oil. The pressure will find a way out!

I have a 4Qt stainless steel tank in the works, it'll be VERY nice and slim to fit nicely..

My '75 2.0 w/d-jet didn't have them but I installed them when I rebuilt the motor.

QUOTE (Jake Raby @ Feb 6 2006, 09:19 AM)

engines that can't breathe don't have all their power freed up AND they leak oil. The pressure will find a way out! I have a 4Qt stainless steel tank in the works, it'll be VERY nice and slim to fit nicely..

Exactly... no wonder the left side leaks and the right side is dry. I ran the engine once with the crankcase vent plugged and the thing was dripping every 6".

I have no PCV, converting carbs to megasquirt.

So if I run all 3 into a contained with a filter and fluid resevoir i'm ok?

QUOTE (yarin @ Feb 6 2006, 08:28 AM)

Yea i figured that. There is no vent box on my car. What connects to the vent box? Left head, right head and the vent next to the oil fill?

like so ...

Is there a breather on that? Filter? What's the internal construction?

I'm guessing its a do-it-yourself item with either welding skills or PVC.

they have a metal perforated screen, then a foam element.

the lid is "offset" so the pressure vents from between the lid and the case...

There seem to be some mixed signals about which cars had them. I didn't think any of the 75 or 76 models had them. Mine doesn't. At any rate...

With the vent next to oil filler and no PCV valve, on a car that did not have head vents stock... is there any potential benefit to adding head vents or is that redundant?

I found a few:

JC Whitney

http://www.jcwhitney.com/autoparts/ItemBro...022887210518365

http://www.cbperformance.com/catalog.asp?ProductID=238

I can't tell if they have 2 or 3 nipples.

I take it you have to periodically check on the foam pad and clean once in a while? Or does the system dump into a tank?

Thanks

your supposed to mount it high enuff where it will drain back into the heads.....

QUOTE (yarin @ Feb 6 2006, 11:16 AM)

Is there a breather on that? Filter? What's the internal construction? I'm guessing its a do-it-yourself item with either welding skills or PVC.

CB Performance unit. has a filter element in it. any oil vapors that make it up there will be collected and drain back into the oil-filler ...

btw. depending on the engine RPM the head vents sometimes SUCK in air ...
Andy

QUOTE (Rand @ Feb 6 2006, 11:43 AM)

With the vent next to oil filler and no PCV valve, on a car that did not have head vents stock... is there any potential benefit to adding head vents or is that redundant?

I sure would like to hear an answer to this.
Anybody willing to comment??
I'm at a point where installing this is still simple.

Basically the crank case vent vents the case, and head vents the heads. The heads and case do have a pathway between them, via the push rod tubes, but they evidently did not flow enough to vent the heads via the case per the factory. The pushrod tubes are used for oil flow back to case.

You will improve ventalation with head venting. The head is an area of potential oil leak (big leak prone gasket) so extra venting of it may help leaks specifically from that area more so than from say the case halves.

If it is easy to ad at this point it might be worth doing. I have run 1.7l stock motors without them (early cars lacked them) I have had them not leak much at all, so you not adding them will not for sure cause a leak. But it can help prevent them.

Big faster turning motors require more venting, as they kick up more air/oil, and may have more blow by.

in Summary:

If you are running a stock small motor and don't want to ad them, then don't worry about it too much. early cars lacked them, and they did not have huge leak problems, however it can't hurt to ad them if you want. The amount of power gain with a smaller stock motor is likely minimal cause the pressures are not that high anyway. (a hopped up motor would see more power increase, as pressures can build up much higher unless extra venting is added.)

I would definatly re-attach them if the car was factory equiped with head venting. (just cause the factory had added them for some good reason) and diffenatly ad it to any big high rev hopped up motor for sure.

hope that answers your main question.

As far as where it goes, with carbs you need to vent them into the air cleaner or a breather box. Either method works. If you have a hopped up motor you will have more oil spray, and you either collect it in the breather box, and periodically clean it, or burn it thru the carbs. The factory way with injection was to burn it. The hoses hooked up to the air cleaner. On your carbs you will need to have three fittings, one each for the heads, and one for the case vent lines. they could all go to one carb or spread out on both carbs.

you may need to do some fabrication. If you vent to the air cleaner, and you have lots of blow by and such, you may end up with an oily carb.

good luck! (Nice engine bay, super clean, new hoses! Nice)

PS I wonder if smog laws had the biggest impact on the factories call to ad head vents later in the model years? In which case you would be running cleaner if you ad them??? maybe??? anyone know effect on emissions?

QUOTE (ClayPerrine @ Feb 6 2006, 08:11 AM)

The only 914 without head vents was the 1.8L with the L-Jet system. It uses a different system. If the vents are there, they make the engine run lean.

Clay,
Please explain further.
I'm thinking of installing vents but don't want to open a 'can of worms" being L-jet and all.
Any info would be appreciated.
Thanks

i know they sell vented type I valve covers, maybe type IV exist? if so then you can try it out by swapping the valve covers,a nd see what happens. You'll need to route the hose from under the car, but I think it is a easy why to vent the head without drilling the head. Maybe someone have avented valve cover you can borrow to try out???

My understanding is that L-jets are sensitive to leaks, i have heard a loose oil filler cap can cause issues, i would assume that if that is an issue it would be becasue of loss of ventalation suction if the cap is left open, given that, maybe more suction (ie added ventalation) may not hurt, as it would increase the suction on the engine internals, the opposite of having a loose oil filler cap. this is just an assumption, and it well could be that too much suction could be an issue.

just don't know exactly how an L-jet would react to improved ventilation.

I have not heard of loose oil fillers caps and such effecting D -jets.

The stock L-Jet hose routing introduces crankcase ventilation after the air flow sensor. Which means it's not metered and the fuel is insufficient for the amount of air (lean condition). My intuition would be that by having a leaking oil filler seal would allow the intake vacuum to pull air in past the seal.

Venting the heads to the intake should tie in before the air flow sensor on L-Jet, IMO. Perhaps T-ed with the charcoal canister inlet.

I would tend to agree with Mcmark, if the L-jet "problem" is the case vent line is routed down stream of the air flow meter, then any change in ventilation will effect mixture. If the stock case vent is after the airflow meter, any change to ventalation would have an effect on what the engine gets after the air flow meter. Add more lines after the air meter will likely lean out the car, adding the line before the meter would mean less air entering after the meter from the exisiting set up.

The one option that might work is to seal off the case vent line at the airflow meter,and re-route it to before the air meter, and see what happens, if that works ok, then go and ad teh tweo lines from the heads. This will work IF the L-jet can handle no extra air after the meter rather than teh stock amount of air added by teh case vent only.

So plug the case vent port on the intake, and leave the hose open for a test (it may leak abit of oil but maybe not, cause it at least iit s still vented to air) This test will confirm or not if you can route all three vent lines before the air meter without L-jet probelms.

Thats the best test i can come up witht o see if head venting might work ok with L-jet, if it will work it will likey require all three vent lines moved to before the air meter.

good luck, let us know if you test it out. i would myself by I am a D-Jetter , and the car is broke anyway.

QUOTE (Marty Yeoman @ Feb 6 2006, 08:37 PM)

QUOTE (ClayPerrine @ Feb 6 2006, 08:11 AM) The only 914 without head vents was the 1.8L  with the L-Jet system. It uses a different system. If the vents are there, they make the engine run lean. Clay, Please explain further. I'm thinking of installing vents but don't want to open a 'can of worms" being L-jet and all. Any info would be appreciated. Thanks

The only crankcase vent in a 1.8L 914 is the big one that connects the oil filler neck to the flexible hose between the throttle body and the air flow meter. It is designed to pull the crankcase vapors in after the air flow meter. As pressure builds up in the crankcase it is forced into the air intake. A leaky seal on the oil filler cap results in false air and the car runs lean. If you have the head vents in, they result in false air and the car runs lean.


If you want to use the heads with the vents, just pull the little pressed in tubes and tap in a small metal plug. BTDT.

Hope that clears it up for you.

My car doesn't have a catch can. The head vents feed into the factory 3-way and then into the driver side carb. The PCV valve feeds into the passenger side carburetor.

Is there any downside to this arrangement, other than having to deal with lines in the air cleaner tops?

McMark,

I'm not sure you want to vent oil vapor into the mass air flow sensor. An old engine will dump a lot of oil into a spring loaded sensitive air flow measurement mechanism. Cold dirty oil can get pretty thick.

Talk about lean if ithe flap sticks closed or overreving if it sticks open.....

Ken

Other than the fact that the PCV valve is not getting any vacuum, it will be fine. You may get some oil in the air cleaners, but it should not be a problem.

QUOTE (ClayPerrine @ Feb 7 2006, 09:26 AM)

Other than the fact that the PCV valve is not getting any vacuum, it will be fine. You may get some oil in the air cleaners, but it should not be a problem.

Doesn't the PCV calve go to the air cleaner on a injected motor? Where else would you connect the PCV valve? Where does it go when you use one of those alluminum vents or a catch can?

My current L-jet configuration has the crank ventilation decoupled from the air-fuel stream.
The pipe connecting the oil filler and rubber gooseneck (between the air meter and throttle body) has been removed,
along with the EGR system.
The resulting hole in the gooseneck is plugged.
The vent at the oil filler has a filtered vent installled.
I am looking for a way to contain the oil vapors released at this vent once it saturates with oil.
It really tends to make a mess of things if I don't keep it clean.
I am hoping I can install a closed system (like the one described).
With my situation, I don't see why it wouldn't work.

By the way, I wouldn't introduce any crank vapors before the air meter. Thats just asking for air meter trouble.

Comments???

QUOTE (MarkV @ Feb 7 2006, 11:32 AM)

QUOTE (ClayPerrine @ Feb 7 2006, 09:26 AM) Other than the fact that the PCV valve is not getting any vacuum, it will be fine.  You may get some oil in the air cleaners, but it  should not be a problem. Doesn't the PCV calve go to the air cleaner on a injected motor? Where else would you connect the PCV valve? Where does it go when you use one of those alluminum vents or a catch can?

On a D-Jet motor, the pcv valve connects to engine vacuum.


The L-Jet system does not use a pcv valve.

Just ordered the one from CB performance with a few other goodies.

I called in they said it has 4 ports and 5 feet of tubing in case anyone wants to know.

Oil on the meter vane seems like good enough reason for the factory to add the vent down stream of the vane. Extra oil shouldn't hurt the carb operation. It how my VW's and 356 is set up (factroy set up). My 356 has some valve guide blowby, so the carb does get oily, but it tunes and works just like the other carb that is clean (no vent line on other side carb.)

Guess what it comes down to is how much false air can the L-jet handle before problems in drivability and running, and how much false air extra would be added by head vents.

If head vents were tied into the same line as the case vent, ventalation would decrease over individual hoses, however the ventilation will still be more than a single case vent, and certainly be more even (ie head would recieve direct venting now, verse via the push rod tubes) Over all vent flow would be restricted by going to a single port on the intake manifold, so that should minimize false air, yet still benifit from head venting (with a corresponding decrease in case venting flow) The junction where the hose meet up would be the restirction, down to one hose diameter. same as stock. Additional restriction can be added to the hose to balance the total "false air" flow to the same as that as the stock L jet would see, just is now the same false air flow is from three sources, not just the case.

you could "tune " the restriction with an oxygen sensor to measure and match stock mixture level at the tail pipe (assuming all other engine system are in order).

Make any sense???

QUOTE (Marty Yeoman @ Feb 7 2006, 09:40 AM)

My current L-jet configuration has the crank ventilation decoupled from the air-fuel stream. The pipe connecting the oil filler and rubber gooseneck (between the air meter and throttle body) has been removed, along with the EGR system. The resulting hole in the gooseneck is plugged. The vent at the oil filler has a filtered vent installled. I am looking for a way to contain the oil vapors released at this vent once it saturates with oil. It really tends to make a mess of things if I don't keep it clean. I am hoping I can install a closed system (like the one described). With my situation, I don't see why it wouldn't work. By the way, I wouldn't introduce any crank vapors before the air meter. Thats just asking for air meter trouble. Comments???

That seems to be the best way to run a case and head ventilation system.

OR, if you absolutely HAVE to retain the extra case and head pressure in the L-Jet system, you could tap two more holes into both sides of the filler neck, put ribbed flanges on there. That way it vents right into the filler neck, then back into the intake after the Air Flow Sensor. Mayhaps, this is why L-Jet systems run lean at higher RPMs? Excess crank pressure leads to an increase of unmetered air after the sensor... Sounds plausible. Definitely have to try it out once I get my 1911 with L-Jet going.

I was thinking that if you hooked the vent up to the intake manifold(s) in such a way as to draw a vacuum on the crankcase, this would help performance. The pistons would not need to displace as much air on the downstroke. It could also help with leaks as there would always be negative pressure inside the case(except at wot). The case needs to be sealed well enough that it does not mess up the carb/FI signal. As somebody mentioned, the 1.8s are set up this way.

If I read that the way you meant, hooking up the any extra vent line to the intake manifold anyplace after (ie down stream) of the carborator, or in the case of L-jet the airflow meter, or in D- jet the thootle body, will cause what is termed "false air lean" which means that extra air leaking in will come in after the gas amount has been determined to match air amount, hence the engine will run lean, too much air in the mixture. Now adjustments can be made for that, the factory can compensate, and new cars have O2 sensors which can compesate for some variation in false air introduction.

Now if the engine was totally sealed, air tight, then you would draw a good vacuum on it, how ever that kind of vacuum I am assuming would tend to suck a good bit of air in thru tiny leaks, eventually at least.

The L-jet for this reason (ie it has the case vent routed down stream of the airflow meter) is very sensitive to the oil cap being loose, cause that is aleak that allows more false air. (also dip stip seal, yes there is supposed to be a seal on it.) the more hoses you run to the intake down from the air meter, the more chances of false air.

on my old L-Jet, I machined Delrin plugs to fill up the 2 inlets on the air-intake elbow between the AFM and the throttle body......

no additional air to worry about, what air went past the AFM is the air that got into the motor.....

For the crankcase, I used a catch can (actually a modified Gatorade plastic bottle )

If you design the catch can correctly, you can hook it up to the aircleaner to get some of the crankcase air to be injested into the motor instead of the atmosphere without too much oil vapor being sucked up as well.

So Mikes car with l-jet ought to be able to run just the same with or with out the oil cap on. The crankcase heads, pushrods tubes are no longer part of his intake manifold any longer because of the plugs he made.

Hey mike is that the l-jet you got from me your talking about?

QUOTE (dmenche914 @ Feb 8 2006, 02:58 PM)

So Mikes car with l-jet ought to be able to run just the same with or with out the oil cap on. The crankcase heads, pushrods tubes are no longer part of his intake manifold any longer because of the plugs he made. Hey mike is that the l-jet you got from me your talking about?

exactly.....heck, you could pop off a valve cover and the fuel injection wouldn't know the differance

the 1.8 I bought from you is sitting on my workbench, I broke an exhaust stud on it so I pulled the heads and installed 2.0 heads on it for a while, then pulled the motor to install another 1.8 for the turbo buildup

The pic below is out of the factory manual. It clearly shows that the flow is into the heads, through the crankcase, and out through the PCV valve into the plenum. Seems like using one of these would defeat the factory crankcase ventilation...
This discussion has always bothered me cuz of this. What am I missing?

I believe it is important to take this into consideration if you want to use L-Jet or D-Jet or K-jet variants for a forced-induction setup. All that possible blow-by and excess crank pressure would throw off air-metering systems. I foresee a crank-case breather in my future. Mueller did the smart thing by blocking those ports on his intake boot for his turbocharger setup. That would also pressurise the crank case with the increased air pressure in the intake system from the turbocharger.

I'm guessing that would lead to finding a whole lot more little places where oil would seep/weep/leak out of the case. Or if you got up to 2 bar, maybe blow them valve covers off... that'd be good for a or two