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 Post subject: B18 crankcase ventilation
PostPosted: Sun Jun 07, 2015 9:24 am 
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Joined: Tue Jan 27, 2015 9:46 pm
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On my B18B I have a non-vented oil cap, my air filters don't have any vents on them, the oil breather on the spark plug side of the block is being vented to air with a small K&N filter and the PVC plug hole in the manifold has been blocked off with a bolt threaded in. This is the setup it had when I purchased the car.

I understand that this could give me blowby/seal issues with pressure building up.

I found this page which is helpful:
http://www.sw-em.com/pcv_diagrams_and_notes.htm

So to get it set up properly, I found a vented oil cap and an air filter plate with the tube on it. I'll connect those two easily.

Now what should I do for the PCV valve. The hole in the manifold is threaded and the PCV valves are not threaded. I assume there is something that threads into the manifold and has an attachment for a hose, to run to a PVC valve? Then I would run that hose to the oil breather and get rid of the little filter?

Thanks for you help!

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 Post subject: Re: B18 crankcase ventilation
PostPosted: Sun Jun 07, 2015 9:48 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Dec 21, 2005 8:40 pm
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Location: Calgary, Ab
The way you have it now is just fine, provided you don't mind the emissions contribution or the smell. Crankcase pressure will be slightly over atmospheric all the time. With either of the OE PCV schema, crankcase pressure won't be much lower than it will be as you have it now during part throttle conditions, nor will it be much better during full throttle conditions.

The OE systems WILL, however, have unclaimed and unknown gasses being breathed in for combustion, which is why the racers don't typically apply anything beyone what you've already got going on. You don't know the composition of that gas: some of it is combustion blowby, some is uncombusted blowby, some is oil vapour, and the rest is air. The carburator mixture is coarse enough already, and when tuning on a knife-edge you don't want the "controlled vacuum leak" coming with a PCV system like the OE.

If you're not bothered by trying to max out your engine and want to burn the blowby (like me), which system to use? Either one uses a restricted nipple threaded into the intake manifold. I like the B18 style better, since it puls gasses down through the head, in the same direction that oil is trying to drain. With the B20 style, PCV gas is being pulled up through the head, and in my experience this can cause an excess of oil to stay in the head and even to overflow. My Mini would literally empty itself on a higway trip.

I'm not sure why the factory changed to the "upflow" style PCV, surely the Volvo doesn't suffer the same malady my BMC did, but I plan to run the B18 style in my car until someone can give me a better reason to change.


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 Post subject: Re: B18 crankcase ventilation
PostPosted: Sun Jun 07, 2015 10:38 am 
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Joined: Tue Jan 27, 2015 9:46 pm
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I'm not too worried about emissions at this point. Just want the car to be healthy for the road trip. Is there any benefit to putting on the vented cap and running it to the air filter, but not putting in a PCV valve?

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1967 Volvo 122S
1969 Lotus Elan +2
2000 Subaru Impreza


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 Post subject: Re: B18 crankcase ventilation
PostPosted: Sun Jun 07, 2015 11:54 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Dec 21, 2005 8:40 pm
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Location: Calgary, Ab
RSready wrote:
I'm not too worried about emissions at this point. Just want the car to be healthy for the road trip. Is there any benefit to putting on the vented cap and running it to the air filter, but not putting in a PCV valve?


That I cannot say. The PCV valve is there to reduce flow at part trottle (high vacuum) conditions, so I assume it's pretty necessary. However, the B20 doesn't use a PCV valve so maybe the nipple is a bit more restricted or the flame trap restricts flow enough. The PCV valve is a pretty generic piece, should be readily available at your local auto parts store.


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 Post subject: Re: B18 crankcase ventilation
PostPosted: Mon Jun 08, 2015 11:21 pm 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Jun 14, 2006 4:19 pm
Posts: 2974
Location: Lethbridge, AB
The only thing I can offer is that the B18/B20 systems don't interchange as the blocks are different. The PCV valve on the B18 is mostly a check valve...I've used a generic valve and they work just fine. So that's the advantage, the B20 has no moving parts.

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