Crank Case Ventilation Trouble

[FluoFerret]

Because it is not sucking any air now. Originally cars had a road draft tube that relied on air turbulence to suck crankcase fumes. A better idea was to run a PCV valve that sucked a controlled amount through the carb via manifold vacuum yet not enough to be a vacuum leak. One breather in a valve cover drew in fresh air to displace the fumes. During low vacuum conditions the fumes exited the breather. Emissions later mandated the modern closed PCV system. The PCV valve still sucked a controlled amount during high vacuum, but at low vacuum the tube that goes from the valve cover to the air cleaner took over and sucked the fumes into the carb. Thus you had true full time Positive Crankcase Ventilation. When you ditch the tube to the air cleaner you upset the system. Now the valve cover breather acts like a vacuum leak, causing lean conditions. Older, richer, jetting could stand the extra air but our leaner emissions carbs cannot.

This bit of information is almost nowhere to be found on the internet if you google for pcv-systems and setups. Thank you man, this helps me a lot in understanding why I have this hesitating/deadspot. I will get rid of the breather and route a simple tube to the air-filter

 

[TURNA]

This bit of information is almost nowhere to be found on the internet if you google for pcv-systems and setups.

Thats because he made it up!

 

[Bonnewagon]

information is almost nowhere to be found on the internet

That is because it is ancient history and considered understood by all. The last open system was used around 1967 , and since then it has been closed. When guys ditch parts they often don't understand why they were there in the first place.

 

[Bonnewagon]

Pontiac used this tube to go from the grommet in the valve cover to the small filter on the side of the air cleaner.

 

[FluoFerret]

That is because it is ancient history and considered understood by all. The last open system was used around 1967 , and since then it has been closed. When guys ditch parts they often don't understand why they were there in the first place.

just makes it harder for us noobs to troubleshoot a system thanks to you guys i can learn each other day something new ^^

 

[FluoFerret]

Just another question? I saw on many engines that they only have a hose running to the intake without any type of breather for fresh air. can this be safely done with chevy small blocks too? I would just get rid of the breather and hook up the pcv valve to a vacuum-port on the carb...

 

[MrSony]

Need a pcv valve in 1 valve cover plumbed to the large port (usually) on the base of the carb, and just a hose going from the other valve cover to the air cleaner to get sucked in. Factory air cleaner housings use a crankcase vent filter assembly, usually under $10 at a parts store. Just a little cleanable element in a new housing.

Aftermarket air cleaners usually have a stamped section at the bottom lid to add in the nipple and just vent it into the filter that way. Doing it any other way will probably still work... But not as well as stock configuration.

 

[shoedoos]

^^^^ very good description from Bonnewagon above

 

[Bonnewagon]

Most but not all run the PCV from a grommet on the intake manifold. Some run it from a breathe/filter on one valve cover. I prefer the intake mounted type. Then you can have the air cleaner routed hose on one valve cover and the oil fill on the other. The little filter in the air cleaner Mt Sony shows does double duty. It filters air going into the engine at high vacuum- then grabs any oil from the vapors when drawn into the carb at low vacuum. If there were no way for fresh air to be drawn in then you would get a vacuum situation in the engine. Some racers do that on purpose by mounting hoses on each valve cover and routing them to the exhaust. At WOT the exhaust flow sucks all vapors out and even causes high vacuum which in theory helps seal the rings. I prefer the valve cover hose going to the air cleaner simply because when you have a low vacuum situation such as WOT, that is when blowby occurs the most. Why would you not want the air cleaner sucking vapors at WOT?

 

[FluoFerret]

Most but not all run the PCV from a grommet on the intake manifold. Some run it from a breathe/filter on one valve cover. I prefer the intake mounted type. Then you can have the air cleaner routed hose on one valve cover and the oil fill on the other. The little filter in the air cleaner Mt Sony shows does double duty. It filters air going into the engine at high vacuum- then grabs any oil from the vapors when drawn into the carb at low vacuum. If there were no way for fresh air to be drawn in then you would get a vacuum situation in the engine. Some racers do that on purpose by mounting hoses on each valve cover and routing them to the exhaust. At WOT the exhaust flow sucks all vapors out and even causes high vacuum which in theory helps seal the rings. I prefer the valve cover hose going to the air cleaner simply because when you have a low vacuum situation such as WOT, that is when blowby occurs the most. Why would you not want the air cleaner sucking vapors at WOT?

Sucking Vapors is good, and I want this to happen, still I wonder if its sufficient to have just the pc-valve on one side creating the vacuum inside the crank-case, and not having a breather or hose on the other side going to the filter.