does crankcase need evac system on street with mufflers?

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dragondan64

dragondan64

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Curious as to what is the best system just to keep pressure out of the crankcase on a street engine with full exhaust? I have read some conflicting answers and want to hear from experienced guys/girls whats the easiest best way to do this? valve cover breathers with baffles under so no oil comes out is all I have ever done is this correct?
 
so use one PCV on one valve cover and a simple breather on other? or use 2 pcv valves and T them together with one hose hooking to carb?
 
just one on one valve cover and a breather on the other, preferably with the breather hose going to the air cleaner.
 

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EL5DEMON340 how do you like that six pack with the pumps on the end carbs?
I have been wanting to try some on a 440. Your setup looks good.
 
ssba said:
EL5DEMON340 how do you like that six pack with the pumps on the end carbs? I have been wanting to try some on a 440. Your setup looks good.
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LOVE them!!! they run great and i havent even jetted them just a stab in the dark, i plan on installing a wide band over the winter and will dial them in next spring. heres the write up i did on them. http://www.forabodiesonly.com/mopar/showthread.php?t=275946
 
69_340_GTS said:
One good breather in each valve cover is also a good setup. You don't really need a PCV valve.
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Breathers by themselves aren't enough. Before PCV's, engines had a "road draft tube" that evacuated the crankcase pressure. The end of the tube was cut at an angle and extended down into the airstream below the car, so at speed the air passing by the tube pulled a draft on the crankcase.

A PCV is far more effective, and less messy.
 
You need a breather (a closed filtered one or if it's open run it to the air cleaner as mentioned) on one side and a PCV or an evac line/tube down to the ex system to pull the blowby out of the crankcase. I've heard conflicting reports on if a nipple in the ex pipe at an angle like a hypodermic needle then run it up to the valve cover (the evac system) will produce enough suction. I'm gonna try this if it passes tech. A vac in the crankcase lets the pistons come down easier for more power. Plus I dont like the varying vac leak which is what the PCV system is, manipulating the A/F ratio
 

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Running fine is not the issue.
What happens is over time the pressure inside the engine pushes the gaskets out. This Leeds to o leaks. Inside the engine gunks up pretty badly.

The PVC and the valve cover breather are designed to keep the inside of the engine clean and The other positive is it keeps the pressure down which helps create more HP.
These devices help engine life.
 
Ok going with a PCV valve on one cover and breather on other cover should be good, thanks for all the info and advice.
 
PCV removed moisture in the oils as well as acids and dirty combustion byproducts. It keeps oil clean and keeps varnish off internals. I doubt the weak volume of vacuum supplied through a pretty small PCV valve is going to do anything beneficial for piston travel, let alone even register on a crankcase vacuum gauge when there is a huge breather on one valve cover and constant positive pressure developing through about 16 other places ie. pistons and exhaust guides. It simply pulls fresh air into crankcase and meters the bad into the intake. Even routing it to header exhaust scavengers will help as that does not pollute intake charge.
 
make sure it's hooked to the correct place on your carb. some carbs have a particular spot for PCV, another for power brakes, another for the vacuum advance, another for vacuum accessories (air grabber hood scoops, headlights etc). each port holds a different amount of vacuum, so be sure to get the docs for your particular brand/model of carb so you get it perfect. also the hoses are different than fuel hose (they are not pressurized, they are for vacuum which will collapse after the engine compartment gets all warm and toasty if the wrong type of hose)
they should be capped off if not in use.


here's an example (holley street avenger):

View attachment carb1.jpg

View attachment carb2.JPG
 
69_340_GTS said:
Nice reply. Tell me why. Engines ran just fine this way for decades before PCV was invented back in the '60s.
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pishta said:
PCV removed moisture in the oils as well as acids and dirty combustion byproducts. It keeps oil clean and keeps varnish off internals. It simply pulls fresh air into crankcase and meters the bad into the intake.
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Also - Without the PCV you would have water vapor (blow-by) condensing on the inside of the valve covers when cooling, forming that icky emulsified grey sludge .. Oil would have to be changed more often as that nasty abrasive black carbon from blowby,, and water vapor would remain in the crank-case and have to be absorbed by the oil..
 
rumblefish360 said:
Running fine is not the issue. What happens is over time the pressure inside the engine pushes the gaskets out. This Leeds to o leaks...
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How is it building up pressure when there is a big hole in each valve cover, totally open to the atmosphere? I have been running my 340 with a K&N breather in each valve cover for 7 years and the engine is as clean as an operating room inside, doesn't smoke, runs great, and the only leaks it has is some coolant seepage. No oil leaking anywhere!
 
todays oils are years ahead of yesteryears dino non detergent oils. You are just doing your air quality an injustice by not allowing your motor to harmlessly injest and burn off some of that crankcase byproduct. 2 breathers will just vent it all out under its own pressure. How does your garage smell the next morning? Synthetics run very clean too.
 
moparlover said:
.............. each port holds a different amount of vacuum, ............
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Manifold vacuum is a constant, doesnt matter how small of an orifice you pull it from, its still the same pressure, the area of the dashpot dictates the force it can manipulate. Sounds like you are talking about timed vacuum ports, ie ported or manifold. Your pic is a great source.
 
With breathers your essentially equalizing the presure in the engine to the atmosphere. Not really PULLING out vapor,condensation. With the PVC it's always pulling cool air into the engine plus filtered if it's connected to your air cleaner + when at wot your vacuum is to low so the PVC is closed and not pulling air in but if the breather is hooked to the aircleaner there will be a slight draw and all blowby which hopefully will be next to nothing will get pulled back in through the carb.
 
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