Valve cover breathers - yes or no?
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Valve cover breathers - yes or no?

  1. #1
    Off Road Badass Bonzen's Avatar
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    Default Valve cover breathers - yes or no?

    I'm running a 2" dia valve cover breather on each side of the motor. No PCV valve or anything. I am getting a small amount of oil misting and recently a oil leak at the back of the intake manifold where it mates to the flat part of the block valley (between cylinder banks) I had sealed this all with a liberal amount of Ultra Grey RTV but it recently started leaking.

    Question is should I be running these breathers, or should I switch to a PCV/hose system that vents the pressure and oil fumes back into the air filter? I have read that just using breathers doesn't really vent the pressure as well and having the intake "suck" the pressure from the crankcase. Bottom line I don't want excess crankcase pressure blowing oil seals or RTV out and making leaks everywhere. Whats the best setup? (Motor is fuel injected, if that makes a difference)Click image for larger version. 

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    Last edited by Bonzen; 07-17-2017 at 02:55 PM.
    "I'd love to help you out wags, but there is larger issue concerning breast cup sizes on another thread that we have to work thru first. This subject suddenly became a non issue." - GN7

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    Senior Member bville's Avatar
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    Breathers have worked for as long as I have been around if your rings are sealed.However I can only see small breathers and by small I mean by how much it will pass(flow) at its smallest point not how big it is on top.Also pull it off and look up in it and make sure it is opened up.
    Having said that running lines to your air cleaner is a viable alternative esp.with having an engine cover.
    Last edited by bville; 07-27-2017 at 10:11 PM.

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    Senior Member SoldHondaBoughtHondo's Avatar
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    The pcv deal only works at idle/low rpm/load when intake vacuum is high. More load/rpm means a higher volume of blowby gases need someplace to go. If you put filters on both valve covers all you are doing is plugging the inside of the filters with oily vapors that at some point will begin to restrict flow which starts to build pressure in the crankcase which will try to push oil out gaskets and causes drag on internal engine parts. Everybody has their own preferences but I have had good luck with a breather in each valve cover...the chrome ones with the 7/8 nipple that sticks out at a 45 degree angle and they use the extra large grommet in the valve cover. The idea being that a large hole means the gasses are moving slower than through a small hole...the breather is actually oil separator and slower moving gives it more time to work...I run a hose from the nipple to a bung in the collector with an old school smog pump check valve to keep exhaust from blowing back into the valve cover..And...if you get the bung set up just right it might be worth a few free horsepower..exhaust gas blowing past the bung trys to pull from the crankcase and reducing pressure in a crankcase is always a good thing. And there should always be some kind of deflector inside the valve cover so oil from valvetrain cant squirt directly into the breather.

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    Off Road Badass Bonzen's Avatar
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    Thanks for the replies. My main concern is to not cause excess pressure and have oil leaks. Also to keep the oil contaminant free (as much as possible) from blow by contamination. I have put the venting system back to stock, since it is an under hatch motor. Vent hoses routed to the air cleaner to help suck the blow-by fumes out at higher rpm. At idle, it doesn't make much pressure as stated so not really an issue, but it can still vent. I "hope" the blow-by fumes don't screw with the A/F ratio. It's not full vacuum like a PCV system, but there should be a good amount more of a scavenging effect when that throttle body is wide open and helping to pull air through the vent hoses.

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    The setup of using the exhaust pulses to pull out the crankcase pressure is a cool idea. I have wet logs so I would have to make sure I don't get any water or excess condensation traveling back into the heads.
    "I'd love to help you out wags, but there is larger issue concerning breast cup sizes on another thread that we have to work thru first. This subject suddenly became a non issue." - GN7

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    Village Idiot fc-Pilot's Avatar
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    Your setup is just fine running to the air filter like that. The factory car stuff often times has that that same hose setup, but it runs to the duct system AFTER the air filter. This creates a stronger suction on the crankcase. The systems in the 60's and 70's used a little filter to keep the potential oil mist from getting too much in the oil intake system that the baffles did not get in the first place. The best would be the factory style but yours should work just fine.

    Paul

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    Member Tahoe540's Avatar
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    I am going through this right now and sick of the mess the breathers make so I am going with this setup to a 1.5 quart catch can https://www.cantonracingproducts.com...-WITH-PETCOCK/.

    All lines are 12 AN and the valve cover fittings are fuel cell bulkhead fittings.
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  9. #7
    Off Road Badass Bonzen's Avatar
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    Ran the boat last Sunday at the lake. Seemed to run fine, no noticeable acceleration difference or anything that in my mind could equate to the hoses venting into the air cleaner.

    Did not notice any oil leaks coming from anywhere on the engine, except where the dip stick plugs in. And that was very minor, like a slight trickle.

    Also, no oil mist all over the valve covers was nice.

    I honestly thought about using the exhaust to "suck" the pressure out like SoldHondaBoughtHondo's setup but being that I'm running wet logs, I'm not about to risk water or lots of moisture running backwards into the valve covers from the exhaust. Shouldn't happen but you never know.
    "I'd love to help you out wags, but there is larger issue concerning breast cup sizes on another thread that we have to work thru first. This subject suddenly became a non issue." - GN7

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    Default Pcv.....

    Quote Originally Posted by fc-Pilot View Post
    Your setup is just fine running to the air filter like that. The factory car stuff often times has that that same hose setup, but it runs to the duct system AFTER the air filter. This creates a stronger suction on the crankcase. The systems in the 60's and 70's used a little filter to keep the potential oil mist from getting too much in the oil intake system that the baffles did not get in the first place. The best would be the factory style but yours should work just fine.

    Paul
    Paul, the little "bow tie" in the outer portion of the a/f body is actually filtering the air going into the engine ( that hose is outside the airfilter's clean air) as the PCV valve sucks it through... While it would also prevent the "misting" of oil vapor going the other way, that condition is usually reserved for excessive blow by engines... A properly ringed engine can survive quite nicely with a simple breather on one valve cover, and a PCV valve on the other with the hose going to the bottom of the carb or another manifold vacuum source... A set up coming from the A/F to the valve cover and the other side through a PCV to manifold vacuum... "Positive Crankcase Ventilation"....

    Ray
    Last edited by Moneypit; 08-03-2017 at 09:06 PM.
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