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Thread: PCV valve

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    Member stevolwevol's Avatar
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    Default PCV valve

    Is it necessary to have the PCV valve routed into the carb? I can help but to wonder why all those crankcase fumes needs to go into the carburetor. Can it be plugged at the carb, and a breather installed instead?

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    Administrator Tom Bryant's Avatar
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    The idea is to run the crankcase vapors through the intake to burn them using engine vacuum. It's an emissions thing. Before PCV systems the oil fill tube would have a vented cap on it and there would be a road draft tube sticking below the rear of the engine. Air flowing over the open end of the tube would cause low pressure and suck vapors out of the crankcase into the air stream under the car while fresh air came in the oil fill tube. You could remove the pcv and run vented caps on the valve covers to relieve crankcase pressure but there would be oily vapors vented out in the engine compartment that will coat things with an oily film. If the engine is worn oil could actually be blown out of the vent caps.

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    Remember the tar strips in the middle of the roads on each lane before PCV valves? I remember as a kid having to walk over them.
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    I remember. Also you would pull up behind a car at a stop sign and see a puff, puff puff of white smoke out of the road draft tube if it had a worn engine and with bad rings the underside of the car would be covered in oil. Made it easy to tell if the car had a bad engine when used car shopping though.
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    Well, I was thinking of venting it instead of letting all that junk coming from the crankcase go into the intake. My engine is has only about 10000 miles on it, but crankcase gasses are still there. When I removed the stock intake to replace it with a performer, I noticed how dirty it was, possibly due to the way the PCV is set up. I could leave the PCV in, and put a vent on it, or remove the PCV entirely, and just having a vent cap like I have on the other valve cover. Would that work, or will I still get oil coating my engine compartment?

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    Quote Originally Posted by stevolwevol View Post
    Well, I was thinking of venting it instead of letting all that junk coming from the crankcase go into the intake. My engine is has only about 10000 miles on it, but crankcase gasses are still there. When I removed the stock intake to replace it with a performer, I noticed how dirty it was, possibly due to the way the PCV is set up. I could leave the PCV in, and put a vent on it, or remove the PCV entirely, and just having a vent cap like I have on the other valve cover. Would that work, or will I still get oil coating my engine compartment?

    The crankcase vapors will accumulate under your hood area, which is why the pre '64 vehicles had a down draft tube almost to street level.
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    Quote Originally Posted by LLC5 View Post
    The crankcase vapors will accumulate under your hood area, which is why the pre '64 vehicles had a down draft tube almost to street level.
    Ok, there was a tube that long. BUT, would having a breather with a filter prevent this?

    By the way, my 69 Ford F100 had the same thing, a down draft tube, so it was being used post 64 maybe, unless it was arranged that way by a previous owner.
    Last edited by stevolwevol; 05-10-19 at 07:46 PM.

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    Quote Originally Posted by stevolwevol View Post
    Ok, there was a tube that long. BUT, would having a breather with a filter prevent this?

    By the way, my 69 Ford F100 had the same thing, a down draft tube, so it was being used post 64 maybe, unless it was arranged that way by a previous owner.

    Or it was an older engine. Possibly California started in 1964 and the Feds later on.


    A filter may slow it down, but if and when that filter clogs the crankcase pressure will vent somewhere which is either your engine bay or gaskets.
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    Quote Originally Posted by LLC5 View Post
    Or it was an older engine. Possibly California started in 1964 and the Feds later on.


    A filter may slow it down, but if and when that filter clogs the crankcase pressure will vent somewhere which is either your engine bay or gaskets.
    So far what I have learned from this thread is to just leave it the way it is. It wouldn't be real stylish to have a hose hanging near the ground, and probably wouldn't work with headers. I have seen that junk that looks like black molasses inside the intake, and in carburetors, probably from years of returning crankcase gasses into the system, so that's why I considered deleting it.

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