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For comparison, I'm running 10.7:1 scr and have about 30K miles on my bottom end and about 5K miles on my top end build built by myself. I'm just wondering why so many guys have problems with crankcase breathing leading to carbon buildup on intake valves, oil misting/dripping, to name a few. If at some point down the road I get problems like yours I will go the catch can route to keep the oil out of my intake manifold.
It must have something to do with the design of the breather your using. Maybe yours drains back into the valve cover vs onto the valve cover.
I doubt you built a blowby free engine.
For comparison, I'm running 10.7:1 scr and have about 30K miles on my bottom end and about 5K miles on my top end build built by myself. I'm just wondering why so many guys have problems with crankcase breathing leading to carbon buildup on intake valves, oil misting/dripping, to name a few. If at some point down the road I get problems like yours I will go the catch can route to keep the oil out of my intake manifold.
Have you taken the intake manifold off to look into the ports at the valves? You can have an intake manifold that looks completely free of oil on the inside, but when you take it off and look at the valves you find buildup on them. My engine is an example of this. I've seen it a lot of times before too.
My vacuum port for the PCV valve is on the back of my carb. When I pulled the carb off, the intake was clean and dry. When I pulled the intake off I found buildup on the 4 rear cylinders and not much on the front 4. The valve stems looked dry and the valves didn't look like they do when a valve seal is leaking, the buildup was much dryer. I don't think it's a coincidence that the valves closest to the vacuum port had the most buildup.
Now I'm not talking a huge amount of buildup on the valves, nothing like if the seals were leaking, but it was buildup just the same. Carbon buildup on the valves has a drastic effect on airflow, especially low and mid lifts. I didn't spend all the time and effort on these heads to get them to flow huge air through all the lift ranges to loose it to carbon buildup, hence the Mopar breather and catch can.
I was still seeing oil mist/drips around the valve cover ports no matter the set-up so tried a different method.
I added two small oil catch cans, one for each valve cover, and routed the hoses from the covers to the cans then to the carb vacuum port using a tee, so both valve covers can vent equally.
Much nicer setup, but did see a small amount of oil at the valve cover grommets. I took everything out of the covers and inspected the baffles, They are in place but I noticed that they both are very close to the valve cover vent holes. Making a few measurements I've found that no matter what type of vent fitting or breather fitting I use, they bottom out on the baffle - effectively blocking the venting. I did not want to remove/modify the baffles so I shortened both vent fittings and after a good hard run I didn't see any leaking!!
Believe I have solved my problem....
I have two cheap Mr Gasket breather caps with some sort of filter material inside. I don't have any pcv tube connected to the carb. So, no oil is ever introduced into the intake system. I'm not sure of what others perceive blowby pressure to be in the crankcase but at least one other forum member did a measurement and it was about 1 psi. Near negligible to have any significant effect on an engine that is not used for racing. PCV is positive crankcase ventilation and not a pressure relief valve. One hole in the engine such as the size of a breather cap hole in a valve cover will easily vent any 1 psi pressure created by blowby without a pcv system. Thus, no pressure build up in the crankcase from blowby. Anyway, I use two breather caps and do not have any oil misting problems but I do have an oil free fuel/air vapour going into my cylinders. I also change my oil regularly to rid any contaminants from the blowby.
Jim T. You are running twin suction with twin oil cans on twin valvecovers. So now, how is fresh air getting into the crankcase if both valvecovers are blocked from getting fresh air?
If anyone runs a evacuation system on a engine, you have to have a fresh-air intake somewhere to replace the outgoing gases (breather) or you are defeating the purpose.
Basically, its the same as running twin PCV valves with no inlet breather.
If you want to test to see just how much oil is getting sucked through your pcv valve just pull the hose off the carb base and put a cheap fuel filter between the line and the carb. Below is what I use for testing as you can unscrew it, clean it out and use it again. You only have to drive it about 10 miles to see if you have a pcv/oil problem and it's cheap.
Seems like nobody mentionned using the exhaust sucion yet, the ideal solution imho, positive crankcase ventilation and no inlet charge contamination. Think they call it An evacusump
If you want to test to see just how much oil is getting sucked through your pcv valve just pull the hose off the carb base and put a cheap fuel filter between the line and the carb. Below is what I use for testing as you can unscrew it, clean it out and use it again. You only have to drive it about 10 miles to see if you have a pcv/oil problem and it's cheap.
Now you guys messed me up. I was perfectly content being dumb and happy with my factory PCV system!! I read this thread, and the previous thread related.
What are your thoughts on the ME Wagner adjustable PCV valve....is this unnecessary overkill or concern? You read their information and they talk about aftermarket PCV valves flowing too much and causing problems like oil leaks. I am having some of that, even on a new built engine with the best gaskets. Is it marketing hype?
I like the catch can I idea that V2 Racing has talking about, and might add this as well as possibly the adjustable PCV valve. Just throwing in some additional thoughts and questions.
Last edited by Torqued Off; 03-18-2018 at 08:54 AM.
The way I worked it out is there are 64 tablespoons of oil in a quart so if you end up with a tablespoon of oil in there after 10 miles you would be burning a quart of oil every 640 miles just through the pcv system. A cheap way to check out the efficiency of the baffles in those aftermarket valve covers and the pcv system. Then if you do have a problem you can fix it if possible or spend a few bucks on a catch can setup.
Seems like nobody mentionned using the exhaust sucion yet, the ideal solution imho, positive crankcase ventilation and no inlet charge contamination. Think they call it An evacusump
Does not work with mufflers.....any backpressure at all negates the scavenging. They are the hot tip to this day for open headers though if not wanting to run a vacuum pump.
The system you speak of was pretty much how oil was evacuated back in the 50s /60s.
It was called a road draft tube off of the rear of intake manifold. It relied on vehicle speed for suction on the pipe connected to the lifter valley to expel vapors. It worked, but todays purist would frown on thousands of gallons of oil droplets on the road.
Then came the bung welded into the header collector with a hose to the valvecover. Same principal. But again, relies on vehicle speed and high RPMs to remove vapor. It does nothing at idle and is likely illegal on the street.
I myself run a simple PCV setup with a Mr. Gasket chrome breather. The 406 only makes 10 inches of vacuum but the system works fine.
Since this photo....I have gotten rid of the line going to the Charcoal canister and changed the PCV to one from an early 80's GM V8.
Canada Grant,,,
I liked your idea about a fuel filter in the pcv hose to measure possible contamination going into the carb. Put one one and went for a "spirited" 30 minute ride and saw only a tiny pin-head speck of oil in the filter.
As mentioned before, I think I had found the problem, the baffles in the tall valve covers placed to high and close to the vent ports thus blocking proper venting. I also adjusted the input pipe inside the oil catch can so that it drops well below the pickup port to the carb.
My set-up now is an oil catch can on the passenger side that connects to the carb vacuum port. And on the driver's side I have a valve cover vent/filter with a very short sleeve into the valve cover.
Think I'm good to go...
Thanks for all the input!!!!
Question: with the factory crankcase vent system, the PCV valve is only open at high manifold vacuum correct? So, when the manifold vacuum is low such as when you have your foot down blow-by pressure i.e. crankcase pressure would be at its highest, at this point does the factory system reverse and then draw this pressure off by sucking back into the air cleaner?
Question: with the factory crankcase vent system, the PCV valve is only open at high manifold vacuum correct? So, when the manifold vacuum is low such as when you have your foot down blow-by pressure i.e. crankcase pressure would be at its highest, at this point does the factory system reverse and then draw this pressure off by sucking back into the air cleaner?
Yes. It just blows up the fresh air intake, and gets sucked into the carb.
02-02-2018, 11:38 AM
