Yes, you can run with only breathers. I personally do NOT recommend it. For proper 'Positive Crankcase Ventilation' you need to have a good vaccum source PULLING the crankcase vapors out. I think if you were to have the exhaust as a vaccum source, you could possibly end up getting more oil and oil vapors in your exhaust than you might hope for and might always smell like burning oil (because it just might be the case).

A couple solid reasons for running a proper PCV system:
1. Creates positive crankcase ventilation (hence 'PCV').
2. Helps seal the piston rings.
3. Prevents excessive pressures resulting in leaking/blown out gaskets and seals.
4. Is for better emissions (I could give a rats ***** about emissions, but #1-3 are enough to over-rule #4).

To counter the oil vapor build up and oil from collecting in your vaccum hoses and your intake and carb, you can purchase an air/oil separator designed for PCV systems. I have a homemade one. I purchased a hollow alluminum enclosed cylinder with the ends capped and drilled/tapped for fittings. I then bought some stainless steel mesh (the same stuff in the home cleaning isle) and string it out and inserting it in one end until it is stuffed fulled. 2 bottom fittings and one top fitting. A bottom for draining and another bottom for the vaccum inlet from the PCV valve. The top fitting is the outlet that goes into your carb. My unit is kinda small I think, so I drain it about 2 times a week and get a few ounces of oil within a week collected. Imagine over time what that does to your intake runners and carb, not terribly bad, but definitely not great!

 

Another issue is that every engine has some blowby into the crankcase. The PVC Valve helps to pull that out. Someone here posted a picture of a totally sealed engine that has a balloon hooked to a tube from the valve cover. When the engine was started it filled the balloon up within seconds of the engine being started.
The amount of CFM pulled by the 1/4 to 3/8 PVC line out of the crankcase in comparison to the CFM of a carburetor is also quite a difference.

 

PCV is the way to go. Granted it doesn't look as cool as 2 matching breathers but without, you will wind up with 2 OIL DRIPPING breathers. Here is mine.

I would however, split the booster to its own source. It needs as high a vacuum as you can pull and I would guess seeing your setup, it is not going to be a vacuum monster.

 

PCV is the way to go. Granted it doesn't look as cool as 2 matching breathers but without, you will wind up with 2 OIL DRIPPING breathers.

You could always go for something like this,

It looks like a breather but is really a PCV made to look like a breather. My brother got this for his 318 we just assembled and tossed into his Dart.

 

Can't just plug the one valve cover like that. It will start to pull valve cover gaskets in to get the fresh air it needs.

Use an oil separator like stated above. I've used them on all of my forced induction cars because they tend to have lots of blowbye during WOT. If you want to cheap out on one use a glass fuel filter with the filter part removed (mount it horizontal), or for a few more bucks get an air/water separator for an air compressor and mount it on your firewall for a finished look. Use 2 barbed fittings and you can get straight or 90* angle ones to make it fit however you want. Just empty them as needed.

 

Thanks for the replies. Anyone else an opinion on vacuum (no flow through, no over pressure) inside the crank case?

 

If you have it no flow through and vacuum you'll find weak gaskets in a hurry. Besides valve cover you can suck in the china wall gaskets easy too. There's really no reason to do it.

 

You definitely need some sort of crankcase evacuation system and that requires creating a negative pressure in the crankcase along with a source for fresh air to get in (breather).

You can create the negative pressure with:

• A PCV valve
• A draft tube
• A venturi in the exhaust
• A driven vacuum pump

In addition to all the reasons given for using crankcase evacuation already stated above, one of the most significant reasons for evacuating the blowby gasses is because they are acidic and will corrode the heck out of your engine's internal parts. Blowby gasses also contaminate the oil.

If you use PCV vs. just breathers, your oil will stay "golden" longer and not turn black as coal like it will without PCV which reduces it lubricating properties.

Not all PCV valves are the same either. You need to select one that is best suited for your engine combo.

A PCV valve operates similar to the power valve in a Holley carburetor. It opens and closes based on engine vacuum. That's why once you start changing cams and other performance enhancements that affect the vacuum signal, the PCV valve might not work properly.

Unfortunately, PCV valve manufacturers haven't been much help to hotrodders and unlike Holley power valves, there isn't a concise selection of them to perfectly match a specific performance engine combo. This has been an issue for years and is why a lot of guys eliminate PCV and just run breathers, but they are doing harm to their engines by doing so. I used to just go get some that were used in 60's performance engines and experiment but that wasn't very scientific or accurate.

Here is a product I've been saying we've needed for a long time. An adjustable PCV valve that you can set exactly for your particular engine combo.

Check it out:

 

You definitely need some sort of crankcase evacuation system and that requires creating a negative pressure in the crankcase along with a source for fresh air to get in (breather).

You can create the negative pressure with:

• A PCV valve
• A draft tube
• A venturi in the exhaust
• A driven vacuum pump

In addition to all the reasons given for using crankcase evacuation already stated above, one of the most significant reasons for evacuating the blowby gasses is because they are acidic and will corrode the heck out of your engine's internal parts. Blowby gasses also contaminate the oil.

If you use PCV vs. just breathers, your oil will stay "golden" longer and not turn black as coal like it will without PCV which reduces it lubricating properties.

Not all PCV valves are the same either. You need to select one that is best suited for your engine combo.

A PCV valve operates similar to the power valve in a Holley carburetor. It opens and closes based on engine vacuum. That's why once you start changing cams and other performance enhancements that affect the vacuum signal, the PCV valve might not work properly.

Unfortunately, PCV valve manufacturers haven't been much help to hotrodders and unlike Holley power valves, there isn't a concise selection of them to perfectly match a specific performance engine combo. This has been an issue for years and is why a lot of guys eliminate PCV and just run breathers, but they are doing harm to their engines by doing so. I used to just go get some that were used in 60's performance engines and experiment but that wasn't very scientific or accurate.

Here is a product I've been saying we've needed for a long time. An adjustable PCV valve that you can set exactly for your particular engine combo.

Check it out:


http://www.youtube.com/watch?v=nd92jPRH3YY

This is pretty cool!

 

I think I will stay away from the "full vacuum" version and rather re-install one breather to give the already installed PCV the chance to create an flow instead of just sucking a vacuum. However what I did was to use a "closed grommet" on the breather side and drilled a 0.1" hole into it just to slow down the pulling a bit and having it pull a little more on the break booster side of the T-joint that way.

The adjustable PCV can be ordered here by the way: http://mewagner.com/?page_id=444

Seems like a killer piece while 130 Dollars is not that cheap though.

Anyway, thanks again for your input guys.

 

Get yourself an adjustable vacume relief valve: http://www.mcmaster.com/#vacuum-relief-valves/=l3k256
So you can control the amount of vacume on the crankcase and also attach a breather to it so the inlet air gets filtered. There's no problem running the T'd vacume hose to the PCV and brake booster-it will work fine. You can also mount a remote resivoir/accumulator with the vacume relief attached to distance this from the engine for less oil vapor if needed. Some also attach two vacume sources so it works in all rpm ranges-PCV and a Pan evac system. At high rpm the PCV mostly works like a vent when the manifold vacume drops to zero and if it doesn't flow enough gaskets blow out, dip sticks pop out...this is where a pan evac system can take over and get the job done.

 

electric vac pump

anybody use them?

 

I know I'm getting one from the link below.

http://www.stevesnovasite.com/forums/showthread.php?p=2038524#post2038524

 

positive crankcase pressure

after reading this thread and some others, i covered the holes in my valve covers with duct tape and started the motor to see what would happen. the pressure from the inside of the motor pushed out on the tape on both valve covers until a channel for air and oil to escape was created and the motor didnt seem to like being choked up like this.
Is this much positive pressure at idle normal?
I dont really want to spend $100 on a pcv valve, but I obviously will if I need to.
My motor is brand new and I'm trying to get this type of thing ironed out before I hit the street.
I was running a check type valve on each side tied into the back of the carb before, but like some other people have said, i didnt really like the idea of the oil and bad air being sucked in the carb.
So am I reading everything correctly that the proper set up in almost any engine combo would be a pcv connected to a vacuum source from one valve cover and a free flowing breather on the other valve cover?

 

after reading this thread and some others, i covered the holes in my valve covers with duct tape and started the motor to see what would happen. the pressure from the inside of the motor pushed out on the tape on both valve covers until a channel for air and oil to escape was created and the motor didnt seem to like being choked up like this.
Is this much positive pressure at idle normal?
I dont really want to spend $100 on a pcv valve, but I obviously will if I need to.
My motor is brand new and I'm trying to get this type of thing ironed out before I hit the street.
I was running a check type valve on each side tied into the back of the carb before, but like some other people have said, i didnt really like the idea of the oil and bad air being sucked in the carb.
So am I reading everything correctly that the proper set up in almost any engine combo would be a pcv connected to a vacuum source from one valve cover and a free flowing breather on the other valve cover?

I run a pcv valve and a breather cap on the other valve cover. My valve covers have baffles and don't suck up any oil. No issues here, idles fine and runs great. :yes::yes::yes:

 

Cant say that I am against PCV, just don't know that I buy the absolute need for a true PCV system. At least not in a hobby application. Better quality oils, probably changed more often then practical, probably not seeing temp extremes of late fall/winter environments to produce condensate. While a good means of removing the air volume within the crankcase to remove unburnt gases and water vapors to reduce sludge and build up is your primary focus. A true PCV system is an emission system to capture and burn unused hydrocarbons added benefits are the removal of vapors and other impurities which can cause sludging.

Seems like a contradiction as we shoot for cool dense air, now lets plug a 250 degree air stream into that carb.

I am not saying don't do it as there are benefits. However realize what your objectives are with your car. As long as you have a breather your engine does have some of it own ventilation do to the inherit blow-by. Especially if it sees any kind of RPM. Thus you get the oil soaked breathers.

I just wonder if PCV vs no PCV would have an effect on a dyno.

 

I can tell you that on a 72 chevy truck that I did a cam/head/intake on after I was done the T they had in the line for the brakes would not work, that being said, I would say adjustable PCV woulda took care of it.