Head vent ports, needed? Options

[yarin]

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

[ClayPerrine]

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.

[yarin]

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?

[Cap'n Krusty]

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

[Joe Ricard]

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

[Jake Raby]

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..

[Allan]

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

[yarin]

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?

[SirAndy]

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 ...

[yarin]

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

[Aaron Cox]

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...

[Rand]

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?

[yarin]

I found a few:

JC Whitney (IMG:http://www.jcwhitney.com/wcsstore/jcwhitney/images/imagecache/I_841053_SW_1.gif)

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

[Aaron Cox]

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

[SirAndy]

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

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

[MartyYeoman]

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.

[dmenche914]

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?

[MartyYeoman]

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

[dmenche914]

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.

[McMark]

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.