There are many ways to evacuate crank case pressure. The oem way is with pcv system but this fails at wide open when the manifold vacume drops off. Exhaust and also acume pumps have been used to pull vacume at higher rpms to take care of the pressure.
Now I was thinking, a typical vacume secondary HOLLEY carb uses vacume to open the secondary blades at wide open. The port is located near the booster and is seperate in function from the base plate ports and timed port. The airflow through the body causes a venturi effect on the port and applies vacume to the diaphram.
Now if a carb had a port opening on each barrel would the combined affects of the four be enough to relieve pressure from the crankcase? Would the booster signal be messed up? If no breathers were used wouldn't the engine have negative pressure throughout unless the rings fluttered? Think about it, maybe some testing is in order. graemlins/beers.gif

Bob

i think the General is one step ahead of you.

http://members.aol.com/joeybsyc/elcoengine.jpg

take a look at this picture of Joey Bs BB which looks to me to be 100% correct, if you look on the passenger side valve cover there is an elbow coming out the valve cover with a hose that runs to the underside of the air cleaner assembly. if you also look at the drivers side valve cover you will see that the pcv valve is also there.

im no expert but it seems to me that the way this system is set up it does exactly as you describe. i havent given this area much thought and currently im not using this breather setup, only a pcv. i wonder if may benefit from getting a stock air cleaner and setting it up the way it was designed. or if would be better off using a vacuum pump setup.

thoughts?

Originally posted by RatONaStick:
Bob

i think the General is one step ahead of you.

http://members.aol.com/joeybsyc/elcoengine.jpg

take a look at this picture of Joey Bs BB which looks to me to be 100% correct, if you look on the passenger side valve cover there is an elbow coming out the valve cover with a hose that runs to the underside of the air cleaner assembly. if you also look at the drivers side valve cover you will see that the pcv valve is also there.

im no expert but it seems to me that the way this system is set up it does exactly as you describe. i havent given this area much thought and currently im not using this breather setup, only a pcv. i wonder if may benefit from getting a stock air cleaner and setting it up the way it was designed. or if would be better off using a vacuum pump setup.

thoughts? Before I became a moron and cut out all my original cowl stuff and the 70 was stocker, it was set up exactly as described above.

I think the stock set up gets the Intake Filter for the filtered inlet air and the suction side is still the PCV valve. Unless the air breather in clogged, you will not get any vacuum in the breather assembly (if that's what I think you are getting at).

basically the way i see the stock system working is the pcv takes care of crankcase evac during idle and part throttle driving. basically anytime there is vacuum present the pcv will work.

But during wot there is no or very little vacuum, so the pcv valve isnt doing anything. this is where the breather assembly works , once there is plenty of airflow through the carb and air cleaner assembly, the suction created by the engine will evacuate the crankcase.

At wide open throttle the pcv system does not work, that's when most people start blowing seals, valve cover gaskets, dipsticks, etc. The vacume port on a Holley vacume secondary carb that controls the opening of the secondaries is a result of high amounts of airflow through the carbs primary throttle bores. Now if ports were existing on all four carburator bores on say a double pumper carb which wouldn't be dependant for opening the secondaries, would the combined vacume from all four throttle bores be enough to evacuate the crankcase when the pcv system fell off at wot? Trace the secondary diafram vacume port on a Holley vacume secondary and you'll see it gets it's signal from near the booster in the main body of the carb, not related to manifold vacume. I think it would work and I'll probably test this when I get my engine up on the test stand. The only thing that concerns me is how much it will affect the booster signal having the port open on all four barrels. Constant negative crankcase pressure should increase ring seal and reduce oil consumption I would think.

Bob
i understand what you are saying, from what i see there is little difference from what you propose and factory evacuation system.

in my opinion that breather assembly that runs from the air cleaner to the passenger valve cover accomplishes the same function.

wouldnt you agree that at wot there is a high amount of airflow in the air cleaner????

With the amount of available air flow within the filter assembly the suction on the breather tube must be minimal, In a cowl induction setup the pressure within the aircleaner assembly could well be positive pressure, no vacume.

now i dunno about that, the only way i see the air cleaner assembly getting positive pressure is if you had a forward facing scoop.

what about cars that didnt have cowl induction? plenty of them on the road. Gm didnt design that breather assembly in there for nothing you know, otherwise they would have never installed it.

you know this breather assembly has its own filter inside the air cleaner, and ive seen them come out pretty oily and dirty. so you cant tell me it has little effect. plus what you propose would have no filters and dump all that nasty crud right into the venturies.

keep in mind im not trying to be rude here, just respectfully disagreeing. :D

Well, how about this: airflow is stupid - so it always take the path of least resistance. In the example of the passenger side valve cover air feed off the air cleaner base: the only way that you will have significant airflow out of the crankcase and through this hose is if it is easier for air to flow this way than through the air cleaner filter into the carb. Given the size of this hose vs the filter inlet area of an open air cleaner I cannot see much chance for this to happen. At best there will be a substantial amount of airflow passing the hose and little suction excavating the crankcase at wide open throttle.

Now let's consider using the vacumn secondary carb diaphram port for high rpm crankcase excavation/ventilation. Yes, there would be enough "suction" off this port. Unfortnately the port size is too small to ever have a chance of being able to excavate any noteable quantity of crankcase pressure.

So most people will always choose between using a pcv system for more regular driving, or very large open crankcase breathers for high speed operation.

Cheap note for street cars that get a lot of dragstrip flogging: pop the pcv out at the drags and pop an open breather in its place.

Thomas

Maybe I'm overthinking this here, but with no disrespect to GM engineering I feel the oil accumulated on your breather filter is a result of the engine belching positive crankcase pressure as a result of poor ring seal-gasses are passing the rings. I do not think the air filter assembly is sucking them out. You will experience the same oil accumulation on a valvecover mounted breather not routed to the aircleaner assembly. My main focus was to create negative pressure in the crankcase throught the rpm range therby producing better ringseal and reducing leakage past the rings. Make sense?

Now let's consider using the vacumn secondary carb diaphram port for high rpm crankcase excavation/ventilation. Yes, there would be enough "suction" off this port. Unfortnately the port size is too small to ever have a chance of being able to excavate any noteable quantity of crankcase pressure.


consider four tied together

There are plenty of cars at the track running low tension rings with vacuum pumps,similar to the A.I.R. pumps on california vehicles. One of the guys that finished behind me in the points chase had this set up and he is going back to regular piston rings and doing away with the vacuum pump, He replaced the vacuum pump a couple times this year. Its more of a pain that what its worth. I just run a K&N filter in each valve cover and suprisingly enough there isn't much oil accumulation on the valve covers,and all my gaskets and seals are intact after two years of full time racing.

just to clarify, my 427 in my chevelle is not using the breather assembly nor is my biscayne. when i referred to seeing the breather filters oily it wasnt necessarily mine, just that i have seen them this way.

anyone know how the vacuum secondaries in a holley get the vacuum to open? there are two small holes in the passenger side venturies of the carb, one in the primary and one in the secondary. the sheer fact that when airflow passes over these holes at a sufficient speed is what causes the vacuum in the first place.

what about the evacuation systems that are used in headers on alot of race cars? they have bungs that are welded in the collectors and tubes that run to the valve covers, when airflow (in this case exhaust flow) passes over these bungs at a sufficient speed it creates a vacuum.

seems like the breather assembly applies here too, the fact that lots of airflow passes over this breather tube in the air cleaner assembly is what causes the vacuum or suction effect.

i just cant believe that the breather assembly was designed by GM for looks, it has to serve a purpose. and in my opinion its function is to supplement the pcv valve when there is no engine vacuum present for the pcv valve, such as wot. i believe a simple test would verify just how much airflow the breather assembly will pass if any at all. remove the breather tube from the valve cover and rev the engine to a few thousand rpms and put your hand over the end of the breather tube to see if there is some sort of suction, if there is some there at 3000rpm imagine what it would do at 6000rpm. i would perform this test myself but i dont have a stock type air cleaner with the breather assembly at the moment.

even though this isnt critical to performance, i think its still worth discussing.

Originally posted by baddbob71:
My main focus was to create negative pressure in the crankcase throught the rpm range therby producing better ringseal and reducing leakage past the rings. Make sense? Bob
it makes sense to me, but my intention was to show you that I believe that the breather assembly was designed for this purpose by GM. it doesnt make sense to me to try and engineer something that was already designed by GM in the first place.

how effective is the GM designed Breather system? i dont know, maybe thats something that should be tested just to find out how effective it is.

Okay i cant sleep, and i had a few more thoughts on this.

after some thinking i dont see how either system whether it be the Stock GM evacuation system with the breather or the system that Bob proposes would create a significant amount of negative pressure (vacuum) in the crankcase. maybe they would create a small amount but i doubt it would have any significant effect on ring control.

i can see however that either design would evacuate any positive pressure that may be there.

the only way i see to create a significant negative crankcase pressure to have an effect on ring control would be to install a vacuum pump, whether it be belt driven or electric.

maybe ill be able to sleep now smile.gif

Sorry to get everybody's gears turning. Looking at this theory, chances are this has been tried before. Does anyone know what amount of vacume a typical evacuation pump pulls? If I drill out one of my carbs for the four port tubes needed and monitor crankcase vacume while testing how much should I be looking for for good results?

Baddbob, you would need to tie together many times the four vacumn ports you propose to get a sufficient volume of airflow. Those vacumn ports are mighty small, and the two used for the secondary diaphram have a very small job to do compared to excavating the crankcase. Nothing wrong with venturing off in another engineering direction - but don't fool yourself for one minute that the hose placement issue has not been thoroughly researched by all the different factory engineers.

Thomas