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,,,,

[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.

[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.