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Small Block Chevy Venting Question.

Discussion in 'The Hokey Ass Message Board' started by Billy the kid, May 29, 2006.

  1. I need to know if this is ok or a bad idea and could cause a potential problem. I'm gonna be running a 1976 or so small block in my T-Bucket and I want to put an old style intake,( one with the filler tube on the front ) on this motor. Will the tube alone be enough ventilation, or will I need to run breathers in the valve covers too? I want to run old cal custom no hole valve covers. Will I need to put breathers in them and a pcv valve or can I get away with just breathers?
  2. 57JoeFoMoPar
    Joined: Sep 14, 2004
    Posts: 5,066


    Personally, I'd run a PCV set up on that motor. The orginal SBCs that had the oil fil tube in the front also had a road draft tube for crankcase ventilation, which you don't have of course. Breathers might be sufficient, but running a real PCV system and creating real negative crankcase pressure would be most beneficial. It is possible to set up the PCV set up with the front filler tube, someone on here did it and it looked clean and worked well. A great trick so you can run smooth valvecovers.
    LOU WELLS and lothiandon1940 like this.
  3. George
    Joined: Jan 1, 2005
    Posts: 7,460


    You should run a PCV valve in one of the valve covers. If you have a filter in the oil cap on the tube that should work.
  4. SinisterCustom
    Joined: Feb 18, 2004
    Posts: 8,269


    Sounds like your doing the same thing that I'm doing. I plan on runnin' my 350 with just the oil fill tube cap as the breather. If things get messy, I may hide a pcv somewhere. Maybe at the back of the intake.


  5. Jethro
    Joined: Mar 5, 2001
    Posts: 1,604


    There was a post about this not too long ago that got pretty heated. The argument was a pcv wasn't traditional and was a "pollution control" device. Anyway it degraded into a schoolyard fight with name calling and mud slinging.
    Here's what I know about pcv....A pcv(positive crankcase ventilation system)is kinda like a bathroom sucks the fumes out of the crankcase and sucks in clean air from the breather. The fumes consist of water vapour, exhaust gas,unburned fuel and other nasties. When the engine cools and there is water vapour and nasties in the motor they condense and create acids and sludge that eat up and bung up your motor.
    I have yet to see a pcv cause any measurable power loss or economy or mileage issue.
    Because it is a "pollution " device it gets lumped in with the inefficient pollution controls like EGR and air pumps......
    Long story short PCV=Good!... NO PCV=not good!

  6. Is that possible, so it's not in the fill tube? What about breathers in the valve covers?
  7. Gator
    Joined: Dec 29, 2005
    Posts: 4,016


    Some of the early Vettes used a PCV valve which threaded into the oil fill tube, makes a nice clean set-up and works fine.
    LOU WELLS likes this.

  8. So no valve cover breathers then right?
  9. Flatbush
    Joined: May 23, 2006
    Posts: 47


    The PCV valve " sucks" air out and you must have some type of air intake. Or the suction will pull oil past the rings or valve guides making blue exhaust smoke
    1Nimrod likes this.
  10. The PCV can go anywhere in the bottom of the intake manifold (that covers the intake valley). It IS a good idea, but not "traditional". I have seen them installed in a threaded hole straight up into the plenum or a runner. Nobody would ever know it's there, but it's a bitch to fix if anything ever goes wrong (TERMINAL vacuum leak). I know the mid 70s Jeeps used a PCV that threaded into the carb base fitting. You could put one of those up through the bottom of the manifold, but you'd have to screen it pretty good to keep out the liquid oil (unless you LIKE giant smoke clouds out the pipes...)

  11. So right in the top of the intake, like in the valley. Or right under the carb. I've never seen it done. Old Vette style in the filler tube sounds kinda cool too.

    I just really don't want to run it in the valve covers.
  12. Gator
    Joined: Dec 29, 2005
    Posts: 4,016


    Right, they had closed valve covers, the oil fill tube up front had a threaded bung and used a threaded PCV. I know the mid-year Vettes (63-67) used this set-up. I know you can get repops from the Corvette restoration places. They come in chrome with a small chrome cap and actually don't look bad compared to a cheap aftermarket tube.

    If you're gonna use a SBC the aluminum finned Corvette valve covers and stuff would at least lend a 60's 'period' look to it. I think it looks cool anyway.

  13. Thats the plan as far as the intake goes, but i got roller rockers and screw in studs so I don't think I can run stock valve covers. I guess I should put a post up for that too.
  14. enjenjo
    Joined: Mar 2, 2001
    Posts: 2,548

    from swanton oh

    Lets get definitive about this. Every engine, old or new creates pressure in the crankcase. It comes from several sources, heating of the oil drives off water vapor, there is blowby on even a new engine, and fuel and other impurities also vaporize, creating this pressure. If you don't vent it somehow, the pressure will get high enough to blow out the gaskets, valve covers, oil pan, rear main seal, ect.

    The old school way of doing it was a breather in the front of the engine, and a road draft tube in the rear. Now a road draft tube is not just a tube. It was extended into the low pressure area under the car, and cut in such a way at the bottom end, that a partial vacuum was created. This kept the fumes from creating a pressure in the crankcase, and blowing out gaskets. The major disadvantage, it vented the vapors into the air with no treatment, and pulled unfiltered air, along with the dust and so forth into the crankcase, where it mixed with the oil creating more wear. Another disadvantage, it doesn't work unless the car is moving.

    In 1963, the California Air Rescources Board mandated that the vapors from the crankcase could no longer be vented into the atmosphere, in the state of California. So all cars sold in California had to have some type of closed system. The Positive Crankcase System was used to comply. It was not new, but had not been used as a matter of course, because it cost the manufacturers more to make it. this system works by drawing filtered air from the air cleaner, and pulling the crankcase vapors into the intake manifold under the carburetor with manifold vacuum. The PCV valve is made to close in low vacuum conditions so the engine doesn't run rough. The PCV valve is also calibrated in size so it doesn't create a massive vacuum leak when open. All PCV valves are not the same. As a plus, the warrantee claims for using oil went down, so by 1965 it was used on almost all domestic cars sold everywhere in the country, even though it was not required.

    So in addition to being a pollution device, which it is, it also makes the engine run better, have fewer oil leaks, and last longer.

    So the elements of a PCV, and a road draft system are pretty much the same, an air inlet, and a vacuum to draw the vapors out of the engine. It's just that the PCV works much better than the road draft tube.

    With a little thought, it's possible to make a completely hidden PCV.
  15. whitewallslick
    Joined: Mar 14, 2001
    Posts: 279

    1. oHIo

    So where is the air inlet in this situation (with a later engine)?
  16. Irish Dan
    Joined: Jan 19, 2006
    Posts: 1,231

    Irish Dan

    I finally "vented" both valve covers on my 68' 327 after having to wipe the "oil mist" my windshield accumulated at highway speeds. Even though I was running the old style "oil tube" intake, I still needed to vent both valve covers! The 327 has a "mild" cam, and maintains about 25 to 30 lbs. of oil pressure when I'm cruising. the oil tube vent idea is a good one that would probably allow you to run the valve covers w/o breathers. Good Luck!
  17. weemark
    Joined: Sep 1, 2002
    Posts: 819

    from scotland

    does anyone have the link to the other post which shows the pcv valve install? i tried searching for it but couldnt come up with anything.

    ive resisted running a pcv valve up to now because i dont want to drill the cal-custom valve covers...but like someone else mentioned im wiping oil mist from the car every time i get out in it, gets a bit tiring after 4 years of it.

    the threaded PCV valve sounds just like the thing ive been looking for..
  18. Jimv
    Joined: Dec 5, 2001
    Posts: 2,924


    I went thru this about a yeart ago on here.A PCV pulls vac. on the engine when its got vac.!! The tube that goes from the other valve cover to the breather( air cleaner) lets the crank breath thru there when theres no vac on the PCV!!The Vac in the carb pulls the fumes, etc. out then.If you ever had vac wipers you'd know that theres not always a vac being pulled.
    Any way, i tried the PCV in the front tube & that doesn't work unless you use a tube with a close cap on it(like the vettes had) but you still need another breather somewhere to even out the breathing.
    on my SBC i have a tube in front with a breather cap, I run "olds" valve covers sometimes( I know it ain't "normal", but i've seen "SCTA" decals on cars that never ran on the dry lakes!!!)Any way what i did on those is i drilled a 1" hole in the very back of the R/S valve( a little bigger in the olds one) covers between The cover & the firewall , put in a grommet & stuck the PCV valve in there, i brazed a small baffle in ther to keep oil out & it work "OK" I still get some oil "dots" on my windshield when i'm doing about 65MPH.But it really hides the PCV.
    I hope this helps ya, but its he easiest way i can explain it.The problem most people ahve undersatnding the PCV system is that they think that the PCV valve pulls vapors from the breather tube to the airfilter in , thru the crankcase & into the carb, which isn't really all true.
    1Nimrod likes this.
  19. hot rod wille
    Joined: Oct 27, 2005
    Posts: 695

    hot rod wille

    I agree with Jethro---pcv's can almost disapear--I did it on my 350 with tri-power

    Attached Files:

    vtx1800 and 1Nimrod like this.
    Joined: Nov 22, 2005
    Posts: 7,591

    from SIDNEY, NY

    My '63 Impala had a PCV valve threaded into a 90 degree brass elbow on the rear of the carb base, and the hose went to a tin fitting retained by one long bolt that replaced the '62 and older draft tube on the rear of the block.
    X-cpe likes this.
  21. FuelRoadster
    Joined: Nov 17, 2005
    Posts: 1,077


    Looks clean,,,how did you baffle the bottom side of the manifold?
    There's a lot of oil activity/mist in those SB lifter valleys.
    Its pulling fresh air thru the filtered,oil fill tube/cap?
    Cool setup man
  22. bobw
    Joined: Mar 24, 2006
    Posts: 2,368


    I have 327's in a couple cars. No pcv systems. If I'm gonna blast down the highway I put a diaper over the filler cap using a wire tie. A shop rag, paper or cloth, or a Harley do-rag works. Keeps the oil mist off the windshield. Around town, I take it off if I feel like it. As for crankcase contaminants, I agree that without a pvc system it will be worse. I suggest changing oil regularily.
  23. hot rod wille
    Joined: Oct 27, 2005
    Posts: 695

    hot rod wille

    The PCV is the metal piece in the hose---it's an in-line on from a Mopar---so it doesn't have a problem picking up oil since it is farther up the hose---and yea--freash air comes in the breather cap.

    Attached Files:

    Tim and 1Nimrod like this.
  24. Clyde
    Joined: Mar 3, 2006
    Posts: 171

    from Las Vegas

    Could you please post the part # for the inline Mopar PCV you are using hot rod wille.
  25. I did the same thing on a '62 283. It was stock with the draft tube and vented fill. A PCV system is definitely the way to go. We have nice chrome valve covers with "Chevrolet" embossed on them, so we did not want to replace them.

    A little searching and I found that the '62 (or '63) vette with the 327 had a filler tube on the front with a non-vented cap. There is a nipple for a medium size rubber hose. I ran the hose from the filler to a nother nipple I installed in the base of the air cleaner. This supplies filtered air to the crankcase. I the filer tube and cap from Corvette Central. They are chrome and very nice, but a bit expensive.

    I then removed the draft tube and replaced it with a '62 vette piece that screws down in the same place. I don't think I was able to find this as a reproduction item, so I bought mine off of Ebay.

    From this nipple you run a hose to an inline style PCV valve, then another hose to the PCV nipple on your carb based or manifold. Neat, clean, works great.

    Would have been a lot cheaper and easier to just replace the valve covers and do it the "normal" way, but hey, this is the HAMB.

    1Nimrod likes this.
    Joined: Apr 17, 2005
    Posts: 1,349

    from New york

    I have a '64 327 in my roadster with just the oil fill tube and a small vent on the front of each valve cover with no issues whatsoever
  27. wayfarer
    Joined: Oct 17, 2003
    Posts: 1,790


    I know this is an old thread, but I'm just getting ready to do this. Here's what I've got: a good running '69 307, chevrolet script valve covers with no holes and two intakes; an edelbrock c3B and a performer. If I've got this all straight I can use either intake, but I'll have to put a threaded hole in either one and use a fitting and an inline PCV. I know I'll have to add the hole for the oil fill if I use the Performer. I need to run an unsealed breather cap on the oil fill tube. Can I hook the inline PCV to the rear port on the carb (an edlebrock performer 600 cfm)?
  28. ray-jay
    Joined: Feb 23, 2008
    Posts: 200

    from Buford GA

    I think most factory PCV valves are placed in some sort of oil separator ie there are baffles below the rubber grommet on the valve covers.
  29. Lobucrod
    Joined: Mar 22, 2006
    Posts: 4,122

    Alliance Vendor
    from Texas

    Yes the 1/4 npt threaded hole on the bock of the carb is the place to hook up the PVC valve.
  30. Danimal
    Joined: Apr 23, 2006
    Posts: 4,144

    1. A-D Truckers

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