gryphon
Club Retro Rides Member
Posts: 330 
Club RR Member Number: 157
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Oct 20, 2019 21:35:35 GMT
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Probably a silly question I'm afraid, but I wanted to check my understanding and some second opinions!
I have a PCV valve that wants to share some space with my intake and needs to be moved. It should sit in the hole in the rocker cover below:
The valve is not sprung so I presumed it relied on gravity to provide the closing force that the vacuum acted against to open it, and was working out a way to mount it vertically elsewhere. The company I bought the intake plenums from then recommended mounting it kinda upside down:
Not clear in the photo, but it's a V6, that PCV is angled down across the head. My understanding is that will just hold the PCV valve closed, and stay closed unless there was a positive pressure in the intake relative to the crankcase.
Seems to me I might as well just delete the PCV and either plug the hole (there's a breather on the other rocker cover), or use it as a breather and feed it into the intake tract (pre throttlebodies)?
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Last Edit: Oct 21, 2019 14:53:01 GMT by gryphon
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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Oct 21, 2019 12:12:46 GMT
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If it's not sprung I cant see how it would work unless it's the right way up.
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gryphon
Club Retro Rides Member
Posts: 330
Club RR Member Number: 157
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Oct 21, 2019 14:26:52 GMT
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If it's not sprung I cant see how it would work unless it's the right way up. Thanks, I agree - I just have someone who really should know what they're talking about telling me otherwise and making me doubt myself. |
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gryphon
Club Retro Rides Member
Posts: 330
Club RR Member Number: 157
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Oct 23, 2019 12:16:18 GMT
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Looking into alternatives that aren't picky about their orientation, these SAAB ones seem like they might be a simple solution? Just an inline check valve... I'm ordering one to experiment anyway. www.ebay.co.uk/itm/SAAB-99-900-9000-PCV-ENGINE-VACUUM-BREATHER-VALVE-7521313 Reading into it more, I'm struggling to understand why one head has the baffles and PCV valve to the vacuum system, and the other head just has a free flowing breather pipe feeding into the intake tract... Is air supposed to feed in through that head and out through the PCV when under vacuum? |
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matty2300
South East
Red ones go faster!
Posts: 157
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Oct 23, 2019 16:08:18 GMT
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yeah sort of, a PCV valve is often sprung - its actually designed to allow maximum flow at low vacuum and low flow at high vacuum (or it would be a huge vac leak at idle) as you rightly figured, the other breather with no valve that's connected to the intake after the filter is designed to allow fresh air into the system There is a decent summary of a basic PCV system on an N/A engine here www.agcoauto.com/content/news/p2_articleid/197I guess on a fancy modern engine if the breather is connected to the intake after the MAF the air passing through the PCV could be metered keeping the fueling correct and the additional air getting past the throttle could somehow accounted for with other methods of idle control, removing the need for a sprung valve?? |
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Last Edit: Oct 23, 2019 16:14:38 GMT by matty2300
2002 Saab 93 - Daily
1972 Vauxhall Firenza Sport SL - in storage
1978 Vauxhall Magnum - PROJECT
1993 Vauxhall Cavalier 2.0 GLS - DEAD
1994 Vauxhall Astra 1.4 LS - DEAD
1999 Saab 93 2.0 SE - DEAD
1999 Mercedes W202/C200 - DEAD
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gryphon
Club Retro Rides Member
Posts: 330
Club RR Member Number: 157
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Thanks Matty, that's a better explanation than I've found elsewhere!
I take back anything I said about just deleting it, and I've found examples of the same part (same P/N) used horizontally in other ford engines so I think mine might just be broken. Guess I'll order a new Jag one as well as the SAAB one.
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gryphon
Club Retro Rides Member
Posts: 330
Club RR Member Number: 157
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Oct 25, 2019 17:16:08 GMT
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Well, new jag valve arrived - turns out my old one was fine! No spring, definitely only works when upright. Even did a couple of (literal) back of envelope sketches to prove my point... Restriction vs Vacuum in different orientations. (no, I don't know why I didn't do flow vs vacuum either). And a basic what's happening...
Hopefully the saab one is sprung, although the ID of the barbs look a bit on the small side.
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