1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Pcv or not to pcv?

Discussion in 'Carb Fuel Systems' started by 82sbshortbed, Nov 24, 2020.

  1. 82sbshortbed

    82sbshortbed Fuckemall!!

    Posts:
    6,846
    Likes Received:
    18,075
    Joined:
    Mar 1, 2018
    Location:
    SE Texas
    First Name:
    Doug
    Truck Year:
    1982
    Truck Model:
    1500
    Engine Size:
    454
    Well, I think I do an experiment with it on and off and see which one seems to be better. It's just that looked it up on line and I noticed that the sbc had a pcv a lot more than the BBC. That's why I was asking about it. I don't see why one would have one more than the other. The BBC just had two breathers and the sbc had a pcv valve.

    So ill do that and report back to see what y'all think. Thanks for the opinions and suggestions. Maybe a pic of your BBC vent systems.
     
    Paladin likes this.
  2. bucket

    bucket Super Moderator Staff Member

    Age:
    39
    Posts:
    22,843
    Likes Received:
    9,030
    Joined:
    Aug 3, 2010
    Location:
    Usually not in Ohio
    First Name:
    Andy
    Truck Year:
    '77, '78, '79, '84, '88
    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    Stock big blocks with no pcv? I've not seen that at all.
     
  3. potent rodent

    potent rodent Member

    Posts:
    38
    Likes Received:
    35
    Joined:
    Mar 22, 2020
    Location:
    indiana
    First Name:
    butch
    Truck Year:
    86 and 78
    Truck Model:
    1500
    Engine Size:
    350 and 305
    put a pvc on it and be done with it the engine needs to breath
     
  4. RecklessWOT

    RecklessWOT Full Access Member

    Age:
    32
    Posts:
    794
    Likes Received:
    1,190
    Joined:
    Feb 20, 2015
    Location:
    New Hampshire
    First Name:
    Kevin
    Truck Year:
    1987
    Truck Model:
    V10 Suburban Silverado
    Engine Size:
    350 TBI
    Nobody's saying to plug it up tight, there's a breather on there already (basically just a tiny cone filter in place of the PCV). The engine can breathe just fine, the only difference is that all those nasty oil fumes from the crankcase don't get sucked back into the intake and dirty everything up, they just get vented out into the atmosphere. AFAIK there is no performance gain or benefit, it is just an emissions device to keep the dirty fumes out of the air, at the expense of your engine's cleanliness.

    They also claim an EGR somehow makes your engine cooler by pumping hot exhaust gas into the intake instead of sucking in a nice cool clean air/fuel mixture. Emissions stuff is for the birds, my old exempt truck ain't single handedly killing the world, though it is a lot cleaner inside...
     
  5. 75gmck25

    75gmck25 Full Access Member

    Posts:
    1,055
    Likes Received:
    668
    Joined:
    Oct 13, 2016
    Location:
    VA
    First Name:
    Bruce
    Truck Year:
    1975
    Truck Model:
    K25 Camper Special TH350 NP203
    Engine Size:
    5.7
    Don’t confuse emissions control with crankcase ventilation.

    All car engines build up moisture in the crankcase because they heat up and cool down, and moisture forms. Without ventilation that moisture just stays in the engine. The moisture combines with the oil film inside the engine and you get a milky mixture.

    In the 60s ( and maybe 50s) most engines had a road draft tube that ran down behind the engine and into the air stream under the vehicle. Air moving past that tube created suction and that pulled moisture out of the crankcase. In the early 70s they switched to a PCV valve in the hose that ran from a carburetor vacuum port to one valve cover, and used a filtered air inlet in the other valve cover. This system functions just like the old road draft tube, but always provides positive pressure to clear out moisture.

    A PCV system may help a little to reduce emissions . However, its primary purpose is to improve the “health” of the engine by removing water vapor from the crankcase.

    Bruce
     
  6. RecklessWOT

    RecklessWOT Full Access Member

    Age:
    32
    Posts:
    794
    Likes Received:
    1,190
    Joined:
    Feb 20, 2015
    Location:
    New Hampshire
    First Name:
    Kevin
    Truck Year:
    1987
    Truck Model:
    V10 Suburban Silverado
    Engine Size:
    350 TBI
    so as long as there is a breather, it can be removed in some way shape or form without that vapor being re-introduced into the intake...

    Internal combustion engines produce pressure which finds its way into the crankcase, as well as the vapors from heated oil in the crankcase. With no vent whatsoever it would just build pressure until it began seeping past seals. A downdraft tube helped direct it down under the car, but with all that pressure suction is not needed for it to find its way out of the engine itself, the tube merely helped it get sucked away from the engine compartment, the pressure would naturally force the fumes out of the path of least resistance, whether that be a PCV valve or a regular old breather. The PCV valve/hose is primarily an emissions device just to stop those fumes from entering the enviornment (and to stop the black oily streaks in the middle of the driven lane we had on roads back in the day). The valve itself can also be a hindrance, once it becomes clogged, which is common, it causes leaks and rough running, where it is very uncommon for a regular vent to become clogged.
     
    Last edited: Nov 25, 2020
    DaleyDriver and 82sbshortbed like this.
  7. Bennyt

    Bennyt Full Access Member

    Posts:
    232
    Likes Received:
    227
    Joined:
    May 17, 2019
    Location:
    Surprise
    First Name:
    Ben
    Truck Year:
    1977
    Truck Model:
    C10
    Engine Size:
    350
    When I was a teenager, I worked at two different dyno shops. At both shops we would swap the PCV valves around or use adjustable ones to get the most power on GM applications and I believe Fords. Chrysler's had a hose that ran to the collector to suck out the crankcase pressure. A breather allows gases to rise but doesn't pull/ suck the gases out like a pcv does.

    Pretty much every vehicle that came in for tuning with 2 breathers left with a pcv to improve drivability and reduce/eliminate engine leaks.

    Not saying I'm right, just what we did at the shops I worked at.
     
  8. 59840Surfer

    59840Surfer Junior Member

    Posts:
    16
    Likes Received:
    35
    Joined:
    Oct 8, 2020
    Location:
    Montana
    First Name:
    Joe
    Truck Year:
    1986
    Truck Model:
    K5
    Engine Size:
    350
    No it wasn't.

    It was a government idea in older gasoline engines with blowby that was decided by a committee to re-route it back into combustion again to extract the last bit of power out of it.

    It originally was an economy device designated as necessary for government contracts to be allowed to various vehicle manufacturers during the war.

    It was a very good idea - but it had several other (good) sidebar things happen that were unseen by the decision-makers.

    1. The crankcase was kept cleaner of consolidated moisture from the byproducts of petroleum combustion and that vapor, when heated, could easily be sent through combustion again and out the tail pipe. A good thing.
    2. Build-up of certain acids and alkalis would constantly be flushed out of the crankcase, prolonging the bearing life and keeping camshaft corrosion to a minimum.
    3. Keeping the crankcase under a slightly low vacuum would tend to keep the old style labyrinthine, leather and waxed rope seals from leaking too badly.​

    Why is it important to mention the camshaft in regard to a PCV System? Because the cam followers are the first place of wear in most engines - until the advent of roller lifters, that is. The seriously small line of contact at any given moment in a lifters life, can create a lot of wear to the cam or the lifters.

    Keeping the oil wholesome was imperative in those days because the thinking was to use non-detergent oils that didn't typically "want" to adhere to all surfaces inside the engines and they were very easily corrupted by moisture, condensate and blowby gases.

    So now - put both the KV and a CV side of a PCV system on your engine for crankcase ventilation and even though it won't hurt performance - it also won't damage the air albeit by just tiny bit. It counts.
     
  9. 59840Surfer

    59840Surfer Junior Member

    Posts:
    16
    Likes Received:
    35
    Joined:
    Oct 8, 2020
    Location:
    Montana
    First Name:
    Joe
    Truck Year:
    1986
    Truck Model:
    K5
    Engine Size:
    350
    For the record and as I remember it when I took my first Smog License Installer/Adjuster/Inspector's test for the license back in 1965, was that the 265 ci SBCs had a road draft tube.

    SOME early 283 ci SBCs had an open system, but not for long.

    I was installing crankcase ventilation after-market systems for those early years - I had the 13th license in California to do that.

    I met a LOT of resistance by the owners of cars that had to have them before their next registration. What with drilling into the intake manifold and threading it for a hose nipple, etc., some guys got quite hostile - but after the owner noticed that his oil stayed cleaner and his engine didn't leak from the valve covers, the oil pan, seals and timing cover, they changed their stories.
     
    Craig Nedrow, Ricko1966 and Shorty81 like this.
  10. Ricko1966

    Ricko1966 Full Access Member

    Posts:
    905
    Likes Received:
    722
    Joined:
    Apr 11, 2017
    Location:
    kansas
    First Name:
    Richard
    Truck Year:
    1975
    Truck Model:
    c20
    Engine Size:
    350
    Surfer59840 after reading what you had written, I had to do some more research, after doing so it seems we are both wrong about its original intention, and it's implementation into automotive use.Anyone here who questions the benefits of running PCV or any form of vacuum crankcase evacuation should jump on the web and do some research.I was already a fan but after research am an even bigger fan.A side benefit non of us except Benny T saw was horsepower gains, not losses. Now moroso and others even even sell high dollar vacuum pumps to clear out the crankcase for even bigger gains, seems like a health pcv pulls 3lbs of vacuum in the crankcase high dollar racers like about 15lbs.
     
    Last edited: Nov 27, 2020
  11. Ken B

    Ken B Supporting Member Supporting Member

    Posts:
    180
    Likes Received:
    67
    Joined:
    Sep 18, 2019
    Location:
    indiana
    First Name:
    ken
    Truck Year:
    81
    Truck Model:
    c10
    Engine Size:
    250
    I just picked up a 85 K10 and someone has plugged lots of vacumn lines and I need to find a diagram on all the vacumn and pcv lines. I dont think this 350 can breathe. any suggestions on where to find a diagram?
    Not original engine so I cant just punch in 1985 K10 and find a diagram
     
  12. dsteelejr

    dsteelejr Member

    Posts:
    49
    Likes Received:
    32
    Joined:
    May 25, 2020
    Location:
    Hudson, WY
    First Name:
    David
    Truck Year:
    1973, 1980
    Truck Model:
    Cheyenne super C20 camper special, Sierra K25
    Engine Size:
    350, 454

    A lot has already been said and a lot of good information given, but I'll throw in my two cents.

    I would definitely run with PCV. Without it your crankcase will slowly vent as positive pressure builds up from blow by and heated oil vapors. Some of the vapors are corrosive and the atmosphere inside the crankcase will remain relatively stagnate. The purpose of the PCV is to have a fresh air draft moving through your crankcase while the carburetor is sucking up vapors. It removes the toxic, corrosive and combustible vapors out of your crankcase and disposes of them by burning them and sending them out the exhaust.

    The 454 I just replaced in my '80 K25 was worn to shit. There was so much vapor coming from the crankcase that the PCV couldn't keep up with it and I had no choice but to vent to the atmosphere. Several time while driving at highway speeds the vapors were enough to give me a headache and make me feel sick. I ended routing the vent hose to where it would exit below the cab and not enter it. Even if your engine is in good shape and doesn't have much blow by I would still recommend using PCV for that reason alone.

    The only drawback I've heard of on a PCV system (and why some people disable it) is because sometimes you can get oil in the PCV system. This only tends to be an issue on newer vehicles, especially with direction injection. If the PCV is connected to the intake before where the gasoline is introduced it can foul up components of the intake. Some people install an oil catch can or disable the PCV entirely. The oil being recirculated through the PCV system can foul the intake valves, but with carbureted, TBI and port injection systems gasoline still passes over the intake valves and cleans them. This doesn't happen with new direct injection systems. I don't feel bypassing the PCV system or installing a catch can is necessary on these older vehicles.
     
  13. MikeB

    MikeB Full Access Member

    Posts:
    1,545
    Likes Received:
    609
    Joined:
    Apr 4, 2014
    Location:
    Justin, TX
    First Name:
    Mike
    Truck Year:
    1982
    Truck Model:
    C10
    Engine Size:
    355
    Even in the pre-PCV valve days, GM knew they had to get combustion blow-by gases out of the crankcase to reduce oil contamination and pre-mature wear on bearings, cam lobes, etc. So they used a road draft tube that dropped down in the air stream to pull a vacuum on the crankcase through the breather on the oil filler tube. It only worked when the vehicle was moving, so it wasn't "positive". On vehicles with dirty oil or lots of blow-by those tubes would emit a trail of smoke. Anybody else remember those days?

    As for hurting engine performance, even the highest performance engines use PCV valves. If you've ever played with one, you'll notice they are only open at moderate vacuum, and are nearly closed at idle and WOT, assuming you have the correct valve for the engine.
     
    Last edited: Nov 30, 2020
    Michael Benardo likes this.
  14. MikeB

    MikeB Full Access Member

    Posts:
    1,545
    Likes Received:
    609
    Joined:
    Apr 4, 2014
    Location:
    Justin, TX
    First Name:
    Mike
    Truck Year:
    1982
    Truck Model:
    C10
    Engine Size:
    355
    Google this and take your pick of diagrams: 1985 Chevy K10 emissions diagram
     
  15. Michael Benardo

    Michael Benardo Full Access Member

    Posts:
    113
    Likes Received:
    42
    Joined:
    Nov 14, 2020
    Location:
    Vallejo, California
    First Name:
    Michael
    Truck Year:
    1973
    Truck Model:
    C 25
    Engine Size:
    292 Cubes
    You definitely should use one, or else you will have poor crankcase ventilation, which leads to excessive oil contamination and if it becomes acidic, corrosive damage to your main, rod, and cam bearings.
     
    Rusty Nail and fast68chevy like this.

Share This Page