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Running dual PCV valves?

Discussion in 'The Garage' started by Burt4x4, Dec 13, 2004.

  1. Burt4x4

    Burt4x4 3/4 ton status

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    On my 350 I had to run two PVCs one on each side due to blow by on one cylinder. This caused my crank case pressure to go way up and puke oil out of the crank seal onto my header and all over the pass side. Adding a second PCV to the pass side fixed the puking of oil.

    On my new BBC I was thinking of just running two PCVs from the get go.

    Does this cause any issues on a new engine?
    Is there such a thing as too much crank ventalation?

    Instead of running a 'breather cap' I am thinking of runnig another PCV?

    Thoughts & opions please
    Burt
     
  2. 84_Chevy_K10

    84_Chevy_K10 Banned

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    How's it going to work?

    How's air going to get into the engine?
     
  3. Burt4x4

    Burt4x4 3/4 ton status

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    So a breather is for letting air in, not out? All the breathers I have allways had seam to get all oily and such so it always seamed to push air & oil out?

    I duno....
     
  4. sled_dog

    sled_dog 1 ton status

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    Tim means that air has to get into an engine. If all the engine does is heat up and push air out then sooner or later it would be a vaccum and we know that is just not the case. Where does the air come from? I really have no idea but I would run 2 PCV valves. My 89 TBI Burb has 1 PCV valve that goes into the base of the throttle body and a breather tube that goes right above the throttle body. So it has 2 suction points ventilating the crank case.
     
  5. madmike

    madmike 1/2 ton status

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    Tim, PCV stands for positive crank case ventilation (but I'm sure you knew that), the inside of the crankcase is under positive pressure (blowing out), the pcv valves relieve the buildup of internal pressure.

    Burt4x4, nothing wrong with using 2 pcv valves, it won't hurt anything, especially having one on each bank of cylinders. I've done the same thing on my bbc.
     
  6. sled_dog

    sled_dog 1 ton status

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    I've run 2 active crankcase ventilation systems on the same motor, many drag racers and circle track cars do it without a problem.

    Tim's line of thinking is a little off I think. hes thinking that if you have to PCVs it will suck the crankcase into a vaccum. In reality this would be ideal. It would lower windage and help power production. In fact thats what Active Crankcase Ventilation does. You install valves in the header collectors then attach them to breathers on the valve cover. The exhaust flow passed these valves in the collector cause a vaccum and suck the crankcase pressure down to about nothing.

    The big differen between standard PCV and the Active setup is that PCVs suck the pressure as well as oil vapor into the motor where it can be burned. If you just suck that into the exhaust emissions will be higher.
     
  7. Burt4x4

    Burt4x4 3/4 ton status

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    Ok cool, Thanks for the info.:D

    Burt
     
  8. rubbinz raczn

    rubbinz raczn 1/2 ton status

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    so sled dog is that why the setup with the pcv's going to the exhaust is racing only, emissions?
     
  9. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    The other thing I'd heard is that the "volume" inside the crankcase is constantly changing as the pistons travel up and down, at any given moment some pistons are travelling up and others are travelling down, but it's not a situation where the "UPs" cancel out the "DOWNs" and pressure stays at 0psi.

    The exact sequence creates variability in the crankcase volume and the excess air needs to have a way to escape.....which I thought was the function of the PCV????


    What the heck do I know....? I can barely even get emoticons to work in my posts these days! :grin:
     
  10. Burt4x4

    Burt4x4 3/4 ton status

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    Ya to me that is what it sounds like he said.

    I can't wait to get my BBC fired up, YukonJack beat me to it! Now that his is running I have to step up and "Get Er Done" hehehehheeh
    Someone call my wife and tell her Christmas is canceled so I can work on my K5 instead of 'doin the hollidays' hehehehe

    Thanks again everyone for the info, great stuff!!
    Burt
     
  11. Burt4x4

    Burt4x4 3/4 ton status

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    I see :D you got it working:) ;) :p:

    You can even change the font

    hehehee
     
  12. Yukon Jack

    Yukon Jack 1/2 ton status

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    We can still have a race for who is road ready first ;)
     
  13. Burt4x4

    Burt4x4 3/4 ton status

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    hahaha OK, deal:D
     
  14. big d

    big d 1/2 ton status

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    how about a pic of how u set setup yur dual pvc setup, please ? thanks.
     
  15. sled_dog

    sled_dog 1 ton status

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    I can't really say thats the reason. I believe it is, its the reason that makes sense. That and I guess there is a chance of flames in the exhaust traveling up those tubes causing a fire, though I've never heard of and really doubt that would happen.
     
  16. Burt4x4

    Burt4x4 3/4 ton status

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    No pics yet, the way I set up my 350 was to simply put a T connector off the vac source on the front then one PVC to each vavle cover.

    That is how I will doit with my BBC too:D
     
  17. tx_sub

    tx_sub 1/2 ton status

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    on my 91 tbi, it has the regular pcv setup and then one on the driver's side valve cover that goes to the spacer ring that fits between the tbi and air cleaner. is that a second pcv? not sure if it has a valve on it per say, but looks like it serves the same purpose.
     
  18. chulisohombre

    chulisohombre 1/2 ton status

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    if you have ever looked at the breather schematic from a stock 72 blazer,it shows one pvc,(right side going from valve cover to carb),and a breather going into the air cleaner(left side valve cover).the thing about having that go to the air cleaner would allow any blowby and oil fumes to go back through the engine and be reburned.this is how mine is setup.but my truck is carbed not tbi.the way you have it that you will set it up sounds exactly the same setup and will keep oil out of your intake with having a pvc on both valve covers.
     
  19. big d

    big d 1/2 ton status

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    k, i get the idea, thanks.
     
  20. 84_Chevy_K10

    84_Chevy_K10 Banned

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    The vent is indeed to allow air in. If you have oil sprewing from one you probably have too much blowby.

    The idea is for air to come in one side of the engine and out through the PCV valve. The idea really isn't to create a vacuum as much as it is to reduce the positive pressure to zero.

    I can't see how two PCV valves would help. I can tell you that running without one will make for a leaky engine though. :)
     

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