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Thread: why no pcv valve on thor 4.0 V8?

  1. 24th March 2011, 07:00 AM #1
    phuma Guest

    why no pcv valve on thor 4.0 V8?

    A simple question - why does the 4.0 V8 (thor version as used on Disco 2s) not have a proper PCV valve? It only has a little oil strainer on the non-breathing side of the crankcase ventilation system - as in here.

    I am sure that at overrun, with the vacuum at it's largest, there will be too much oil vapour going into the intake. "Other" PCV systems usually have a valve that restricts the PCV opening depending on vacuum.

    Ideas?
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  2. 24th March 2011, 07:41 AM #2
    bee utey's Avatar
    bee utey
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    Quote Originally Posted by phuma View Post
    A simple question - why does the 4.0 V8 (thor version as used on Disco 2s) not have a proper PCV valve? It only has a little oil strainer on the non-breathing side of the crankcase ventilation system - as in here.

    I am sure that at overrun, with the vacuum at it's largest, there will be too much oil vapour going into the intake. "Other" PCV systems usually have a valve that restricts the PCV opening depending on vacuum.

    Ideas?
    The kit you linked is for a GEMS engine. The THOR engine PCV connects from the drivers side rocker cover to the inlet plenum. The breather from the throttle body is the fresh air intake.
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  3. 25th March 2011, 06:11 AM #3
    phuma Guest
    Sorry - wrong link! But the principle is exactly the same - without a PCV valve. And that I find a but curious - or is this setup without a PCV valve common?
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  4. 25th March 2011, 07:01 AM #4
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    bee utey
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    I must not have looked closely at the Thor, no reason why you couldn't fit a pcv in the RH breather. This side connects to vacuum, probably with a restrictor, the other side gets air flow at the throttle body to suck in the excess fumes.

    PCV systems seem to be an American invention, so commonly seen on Aust and Japanese cars too. Not so much in European cars. So whatever meets your emissions rules I guess.
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  5. 25th March 2011, 09:07 AM #5
    PhilipA
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    AFAIR no RV8 has ever had a PCV valve.
    The 3.5 had 2 vents to the carbs.
    The 3.9 has a straight vent to inlet with a vacuum bleed into the plenum and so on.
    The Thor has a one way valve on the air to crankcase inlet which I presume reduces hydrocarbons venting to atmosphere when stopped.
    Regards Philip A
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  6. 25th March 2011, 09:45 AM #6
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    POD
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    Back in the day, I was taught that the PCV valve is there to prevent flame from a backfire from igniting the blow-by fumes in the crankcase, not to restrict ventilation at overrun. The older rover V8s have a gauze flame-trap for the same purpose, i.e. there is still Positive Crankcase Ventilation but with a different means of preventing a backfire from turning the crankcase into a bomb. Also if I remember correctly (which is not always the case these days), the crankcase vents upstream of the throttle butterfly, so overrun vacuum is not applied to the crankcase anyway.
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