case and head vents, do I need to run a breather box? Options

[wayne1234]

Ok dual webber carbed 2.0, I think the PO had the head vents running to a T then to the oil breather near the oil cap... Is this right?? I did a search and now I'm really confused,,,,

[Cap'n Krusty]

Dumb. No, make that stupid. What ever possessed him to vent the engine into itself? Yes, you need a breather box, even though it's illegal by Fed law. Vent the box ionto one or both air cleaners, so it at least looks legal. It's probably a leaker, and proper ventinmg should take care of that unless the seals are blown. The Cap'n

[wayne1234]

This is a completly rebuilt engine I am just putting it back in the car now, setting up things, and it didnt seem right,,, is there a how to or a write up I couldnt find anything straight forward when I searched... Thanks

[rick 918-S]

Someone will have photos for you. I wish I were as smart as the capt. I could try to draw it out for you but stick men won't due in this instance. Best wait for someone else. (IMG:style_emoticons/default/biggrin.gif)

[ChrisFoley]

This is an install pic of the Tangerine Racing Breather Can that incorporates the features Cap'n Krusty recommends.

Both heads and the crankcase are vented to the cylindrical canister.
The canister is designed to effectively separate any oil from the vapors and return the oil to the engine via a bottom drain hose.
The top of the canister is connected to both air cleaners so all the vapors are integrated with the engine intake air.
Therefore no atmospheric contamination or oil mist in the engine compartment.
(IMG:http://www.tangerineracing.com/images/EnginePics/InstallationWithIntakeSuction02.jpg)

[Cevan]

I've seen these arrangements setup a couple of different ways; either venting the vapor back to the top of the carb air filters (like the photo above) or out thru a small filter into the engine bay. I like Chris' setup in that there's no oil vapor escaping into the engine bay and making every speck of dust stick to the motor.

Is it necessary to use the spark arrestor that the stock D-Jet uses to tie the two nead vents together before venting to the cannister?

[ChrisFoley]

Is it necessary to use the spark arrestor that the stock D-Jet uses to tie the two nead vents together before venting to the cannister?

Much better to go directly to the can, at least with ours.

[Gint]

Link to a 914world search for +head +vent

A search for +oil +breather will yield lots of previous threads on the subject also. Here you go...

Link to a 914world search for +oil +breather

[pbanders]

Note that even the Tangerine solution, which is the best one I've seen for carb setups, doesn't provide the same function as the factory system does. The factory system is a true Positive Crankcase Ventilation (PCV) system, that uses intake manifold vacuum to scavenge crankcase vapors. The Tangerine system (and other passive breather systems) depend on crankcase pressure alone to transport vapor to the system. The factory system uses an active PCV Valve mounted on the oil filler box to manage the system across a wide range of intake manifold pressures and crankcase pressures. There's a writeup on this system at my web page below.

[ME733]

[quote name='pbanders' date='Jan 23 2010, 11:20 AM' post='1264867']
Note that even the Tangerine solution, which is the best one I've seen for carb setups, doesn't provide the same function as the factory system does. The factory system is a true Positive Crankcase Ventilation (PCV) system, that uses intake manifold vacuum to scavenge crankcase vapors. The Tangerine system (and other passive breather systems) depend on crankcase pressure alone to transport vapor to the system. The factory system uses an active PCV Valve mounted on the oil filler box to manage the system across a wide range of intake manifold pressures and crankcase pressures. There's a writeup on this system at my web page below................. (IMG:style_emoticons/default/popcorn[1].gif) .....THE INTERIOR of the air filter housing will have a negative pressure as the carburators....SUCK AIR. Therefore the tangerine system will work identical to the factory setup, providing positive crankcase ventilation....and as venting the crankcase is important, reguardless of RPM,s why would anyone want or need a pvc valve?. The easier the engine "breaths" the faster it will rev. up., and have (fewer leaks) which are mostly caused by excessive crankcase pressure. A very free breathing engine starts with some internal crankcase modifications. (IMG:style_emoticons/default/popcorn[1].gif) Murray

[pbanders]

THE INTERIOR of the air filter housing will have a negative pressure as the carburators....SUCK AIR. Therefore the tangerine system will work identical to the factory setup, providing positive crankcase ventilation....and as venting the crankcase is important, reguardless of RPM,s why would anyone want or need a pvc valve?. The easier the engine "breaths" the faster it will rev. up., and have (fewer leaks) which are mostly caused by excessive crankcase pressure. A very free breathing engine starts with some internal crankcase modifications. (IMG:style_emoticons/default/popcorn[1].gif) Murray

The interior of the filter area of an air filter system like the Tangerine system (common to all Weber/Dellorto systems) is not at low pressure, it's essentially at atmospheric pressure. Yes, there is a tiny pressure differential across the filter element (less than 5 mbar), but if the pressure difference was truly significant, you'd be choking the breathing of the engine. True low pressure is in the area below the throttle plates, in the case of a carb'ed setup, in the runners themselves. Note that this is true only in the case of closed throttle (idle) or part-load (low throttle angle) conditions. When the engine is at WOT, there's only about 20 mbar of difference between the local atmospheric pressure and the pressure below the throttle plate.

True positive crankcase ventilation requires manifold vacuum.

PCV valves operate to control the amount of manifold vacuum used for crankcase scavenging. If you simply hook up manifold vacuum to the crankcase, you've essentially opened a giant vacuum leak. Even if the crankcase is completely sealed, too much vacuum can have other negative effects. The PCV valve controls the vacuum level in the crankcase to avoid these issues.

[wayne1234]

Man I hate to say it but the setup going back into the carb filter tops doesnt look very good,,, kinda cluttered,,, I know it sounds kinda vain but I would like a clean looking setup that would keep oil off the engine,,

[ChrisFoley]

Man I hate to say it but the setup going back into the carb filter tops doesnt look very good,,, kinda cluttered,,, I know it sounds kinda vain but I would like a clean looking setup that would keep oil off the engine,,

This is our original design that has all the same features except the carb suction.
A cheaper product is available from CB Performance that uses a small rectangular box instead of the cylindrical can.
IMO, the volume of the can is critical to effective cranckcase ventilation, and the oil separation features we employ do a much better job of preventing oil mist from contaminating the engine compartment.
If you follow the links Gint provided I'm sure you'll see someone's installation of the CB product.
(IMG:http://www.tangerineracing.com/images/EnginePics/BreatherCanInstalledAlternate2.jpg)

[ME733]

THE INTERIOR of the air filter housing will have a negative pressure as the carburators....SUCK AIR. Therefore the tangerine system will work identical to the factory setup, providing positive crankcase ventilation....and as venting the crankcase is important, reguardless of RPM,s why would anyone want or need a pvc valve?. The easier the engine "breaths" the faster it will rev. up., and have (fewer leaks) which are mostly caused by excessive crankcase pressure. A very free breathing engine starts with some internal crankcase modifications. (IMG:style_emoticons/default/popcorn[1].gif) Murray

The interior of the filter area of an air filter system like the Tangerine system (common to all Weber/Dellorto systems) is not at low pressure, it's essentially at atmospheric pressure. Yes, there is a tiny pressure differential across the filter element (less than 5 mbar), but if the pressure difference was truly significant, you'd be choking the breathing of the engine. True low pressure is in the area below the throttle plates, in the case of a carb'ed setup, in the runners themselves. Note that this is true only in the case of closed throttle (idle) or part-load (low throttle angle) conditions. When the engine is at WOT, there's only about 20 mbar of difference between the local atmospheric pressure and the pressure below the throttle plate.

True positive crankcase ventilation requires manifold vacuum.

PCV valves operate to control the amount of manifold vacuum used for crankcase scavenging. If you simply hook up manifold vacuum to the crankcase, you've essentially opened a giant vacuum leak. Even if the crankcase is completely sealed, too much vacuum can have other negative effects. The PCV valve controls the vacuum level in the crankcase to avoid these issues.

.....................Well you have already explained the situation, and apparently do not understand what your information contains. 1. there IS very little vaccum in the air cleaner. However IF the crankcase pressure IS excessive (like W.O.T.) the pressure WILL be routed to the air cleaner, and there being a (very low negative pressure) WILL be drawn down the carburators....2. With the example you provided...Manafold vaccum...provides...giant vaccum leak...without P.V.C. valve...this is somewhat true. The manafold, runner, which has the vaccum line...will result in THAT PARTICULAR CYLINDER running LEANER/with contaminants/oil.water vapor/hot crankcase air,etc....3. IT is much better to divide /split the crankcase air/vapors/ into ALL the cylinders. This will enable a far more accurate adjustment of /carburator adjustments/JETS to provide optimum performance.3. the possability of having too much vaccum is (O) zero....MURRAY.

[Cevan]

There being a ton of people on this forum running carbs, I'd like to know how your breather is routed (to the carb filters or to the atmosphere via a small air filter). If you route to the carbs, do your carbs stay clean or does the oil vapor gum things up? If you route to the atmosphere, does the vapor dirty the engine bay?

[r_towle]

Cevan,

If you run the oil vapors into the carbs, its much cleaner in the engine bay, period. I will say the net result for me and my personal issue is that I have less oil in the engine bay now...but I found a leaking head vent tube while installing the system...

With the exit gases routed to the carbs, I have this opinion.
The drawback that IC is that now you are once again introducing oil into the A/F mixture which makes the burn less efficient. Spark plugs dont like oil, and IMHO you loose HP.

If you use the original setup Foley makes yet run a hose from the top vent and relocate the exit of that vent somewhere outside of the engine bay, you will get the best of both worlds...

Do not vent it in front of a wheel...oil vapor on one wheel would be bad.

Older american cars just ran a hose with no filter down underneath the car and used the venturi affect to suck the vapors out of the hose.

From personal experience, I just installed the EMPI/CB performance unit and I mounted it right in front of the motor, centered like Foley shows his.
Well, guess what is right next to it. The electrical intake heater fan...
This setup now sucks crankcase vapors (which are not just oil but blowby gases) into the passenger compartment...
I was good for one trip to work and back...now I need to change the output. Headache, CO levels to high and I drove to work and back with the windows open in the winter...not a good setup.

The EMPI/CB performance unit has a raised lid that allows the gases to escape all around the lid. I plan to mill off the raised standoffs and close the lid tight, then add a NPT pipe fitting to the top and remote locate a filter outside the engine bay....somewhere...dunno where.

I wont shoot the vapors into the carbs, I need every spec of HP the little powerplant can produce and IC no logic in adding oil to the mix. My car will never be a green planet saver, nor will it single handedly deplete the ozone layer.

I have all my DD cars running modern FI with all the restrictions. the 914 is a toy and is driven as a hobby car.

Rich

[ChrisFoley]

With the exit gases routed to the carbs, I have this opinion.
The drawback that IC is that now you are once again introducing oil into the A/F mixture which makes the burn less efficient. Spark plugs dont like oil, and IMHO you loose HP.

That could be a problem with the CB product which doesn't have effective oil separation features. Escept on engines that have excessive blowby from worn or poorly seated rings my system is designed to nearly eliminate oil from ever escaping the engine.
Beside that, a healthy engine will produce far less crankcase gasses than the total amount of air entering the carbs. The amount of oil contained in the mix won't negatively influence combustion.

[pbanders]

.....................Well you have already explained the situation, and apparently do not understand what your information contains. 1. there IS very little vaccum in the air cleaner. However IF the crankcase pressure IS excessive (like W.O.T.) the pressure WILL be routed to the air cleaner, and there being a (very low negative pressure) WILL be drawn down the carburators....2. With the example you provided...Manafold vaccum...provides...giant vaccum leak...without P.V.C. valve...this is somewhat true. The manafold, runner, which has the vaccum line...will result in THAT PARTICULAR CYLINDER running LEANER/with contaminants/oil.water vapor/hot crankcase air,etc....3. IT is much better to divide /split the crankcase air/vapors/ into ALL the cylinders. This will enable a far more accurate adjustment of /carburator adjustments/JETS to provide optimum performance.3. the possability of having too much vaccum is (O) zero....MURRAY.

There's a significant difference between passive crankcase ventilation and active crankcase scavenging. The use of crankcase pressure (passive ventilation) as you describe was how it was done on carb setup cars for decades before 1970. Two factors drove manfacturers to adopt scavenging, oil sludging and post-1970 emissions regulations. PCV systems significantly reduced crankcase-based hydrocarbon emissions, and also did a much better job of removing water vapor from the crankcase than the old passive breather systems, resulting in less sludging and corrosion of internal engine components.

You point out the difficulty of incorporating a proper scavenging system when you have 4 separate intake runners with a carb setup, yet another reason that setups like this started to disappear after 1970. Nobody is advocating using a PCV system with a dual Weber setup, it would be very difficult to engineer. The best you can do is with a breather system.

[wayne1234]

ok how about this.. I know an my Audi TT a common "upgrade" is a oil catch can, many people use a air compressor water seperator bulb ... could you use one of these and just route th other side to atmosphere?

[Mike Bellis]

You could do what the V8 drag racers use. Crank case vacuum scavenger tubes welded to the exhaust. They create negative pressure in the crank case and help to seat the rings better and reduce blow by. This setup is not legal to run on the street but know one really checks for this set up. To use it correctly you will need check valves on the scavenger tubes. You would also run a sealed case, no vents other than the valve covers.