What are you guys running for PCV valvves in your B18s?

I spoke to Rhys at Island Automotion who said many of the generic PCV valves that are typically made for American cars but fit the Volvo don't work very well. He said to try idling the car, then clamping the hose that runs from the PCV to the intake manifold. If the revs drop, air is flowing by the PCV at idle, which will have a negative affect on the idle. Sure enough, the revs dropped when I clamped the hose.

I'm running a generic one from NAPA. Volvo can't get me the proper one any time soon. It's been on backorder for a month now with no end in sight. IPD doesn't seem to carry them. Olof might, but he hasn't got back to me yet.

I have some carb issues that Rhys is helping me sort out, but it's probably a good idea to have this all sorted too.

I don't know if what I described to you earlier made sense, but I am not running a PCV valve in my car. I restricted the flow through the hose between breather box and intake manifold with a slug of aluminium that has a small hole in it for the PCV gasses to pass through. In effect, I'm choking down the flow from the 3/8" ID hose to something closer to 1/16-3/32" ID.

PCV valves make no sense to me.

This doesn't have to be anything fancy, just a hunk of bolt with a small hole through the middle, jammed into the hose at one end. I don't have a photo of it, but I have no idle issues. I would venture to guess, though, that no matter how you vent the crankcase to the intake manifold, you're going to be sucking SOME unmetered air through there and altering your idle in some way. Simply saying that if you see a difference in the idle once you clamp off that hose means you have a problem is a bit of a broad and misleading statement.

I've had so much going on in my head that I forgot we even talked about it Matt. I do remember some of the things you said though. Interesting set up you have. I understand what you're doing now.

When I clamped off the hose, the difference was very noticeable. The car actually sputtered and died. I understand having some unmetered air going through, but that seemed a bit extreme. Of course, I'm far from an expert.

All I was saying was that your idle RPM will probably drop SOME when you pinch off that hose. It could be worse if your car is too rich at idle, as pinching off the hose will make it richer, or if the valve is allowing too much air. If you've got a huge cam you may need to have the throttle valves open more at idle due to the reduced vacuum, and the PCV won't flow as much air in that case so pinching it off wouldn't affect the idle as much. If the engine is really worn and there's a ton of blowby, it will affect the idle differently than if the engine has good ring seal. And there's combinations of all these conditions...

There's more to it than just the PCV valve, is my bottom line, and saying that the PCV valve is the problem when the RPM changes a lot is a little too general for my taste.

But based on your engine practically shutting down when you pinch that hose, it suggests that you have a problem and reducing the flow through the PCV system is probably the right move.

For the crankcase hose connection to the intake manifold, I used a brass fitting (3/8"threaded X hose bib ) and drilled and tapped the I.D. I then installed a set screw in which I had drilled a small ~3/32" hole. By using the set screw, I could replace with a smaller or larger drilled orifice depending on how it worked out. No PCV valve.

dean

Here's what you have...



Here's what works better...



B18's and B20 systems are reversed with respect to flow. The B18 block gets a vacuum signal from the intake via the PCV valve (which is just a one way valve in these things), this opens the valve and vents the blow-by into the intake track to the back side of the carbs (this is critical). This gas is then burnt in the combustion cycle. To prevent a vacuum in the block the negative pressure is balanced by providing filtered air from the front carb through the oil filler cap (note the inclusion of an oil separation media in the cap). If this is not functioning properly, then the flow tends to reverse and you get nasty junk accumulating in the front carb which causes them to stick and generally be a bother. Never vent oily gunk into an SU.

The B20 changes the flow up as the other guys are hinting at. Volvo has run this system on (I believe) every engine since the B18...so I change all B18's I see to B20 style as it's more reliable and has no PCV valve at all. I'm showing the FI version as it had pretty arrows. Both of these figures are from the Volvo service manual BTW. Once again, vacuum is generated by the intake, but this hose is connected to the oil fill cap. In order to meter the amount of suction, there is an orifice (as Dean has mentioned) in this fitting (so you need to either make this up or find one from a B20 (or weld up your B18 one and drill a 1/16" to 3/32" hole in it). In essence, there are enough mechanical things in the pathway of the vapor that most of the oil does not make it all the way back up the path and drains back. If you've got really worn rings...this doesn't work. The pressure is balanced through the flame trap on the side of the block which has a strainer on it (wound brass) and is connected to filtered air (to the front of the carbs or FI manifold behind the throttle body. Note the absence of filter media in the oil fill cap. If you switch a B18 to B20 - take the filter media out of the cap (it's probably not there anymore anyway). Later B20's even got a taller cap in an attempt (IIRC) to try to shed more oil/blow by from this pathway to comply with stricter emissions regulations.

In an ideal world, you'd use a puke can and not feed oily vapors back into your engine. The B20 plumbs easily for this.

And as a counterpoint, I personally feel the B18 style is superior, at least in terms of the direction of flow through the engine. I do not like venting crankcase gasses OUT through the valve cover or cap. There's too much splashing going on up there and with the oil trying to flow down the same channels that you're trying to let the PCV gasses flow up, you risk preventing oil from draining at all. I've experienced this in a couple cars with this PCV arrangement, and while it might not happen with the Volvo pushrod engines I'm once bitten, twice shy, and will preach it forever (sorry).

If the B18 routing were designed with a restricted orifice fitting instead of the PCV valve (as Dean and I suggested doing), I am the most comfortable. I'm not saying that the B20 style is wrong or inferior, I just feel better plumbing it like the B18.

Funny, I have no issue with the B18 style either as the pathway is cleaner and the flame-trap more effective in that flow direction. The issue is those silly one way valves, that's the reason I advise changing them to the later style. So either way - get it routed properly for whatever you've got and you'll be fine.