help with boosted pcv setup?

[92cavquest]

I'm getting really close to firing this thing up and it's finally time to address the pcv setup. I've done a little reading up on this and there are alot of different ways people do it and everyone thinks their way is the best. But I'm clueless on this when it comes to a v6 engine. So what I need to know is (short or a vacuum pump) what is the best setup?

Should I just get another front valve cover for the rear and vent them? Should I run a line from each VC to a vented catch can? Please help me. There are too many options.

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[The_Raven]

On every turbo engine I have built, I have used a PCV valve that will close completly, when there is pressure applied to the side where the vacuum line/hose attaches to the intake manifold, and then connected the other side of the PCV system to the turbo inlet/air filter. The only variation I have done to this is on a friends turbo Del Sol, where we installed an oil catch can in the system between the cam cover and the truno inlet.

You may have to find a different PCV valve that will truely close. I have one on my Datsun that is threaded on one side, that I think came from a Mitsubishi minivan. I just went to the Canadian tire aisle that had the PCV valves and found one that looked like it would work. Tested it and it definatly closes off completly.

[92cavquest]

Go go from the crankcase (valve cover) to the intake before the throttle body with a good quality pcv valve? This will let the crankcase breathe without pressurizing it with boost?

Won't that only let the crankcase vent when I'm out of boost or when the crankcase pressure is greater than the boost level? Is that good enough?

I'm not trying to seem doubtful of your methods. I just can't wrap my head around it quite yet.

[MidnightriderZ24]

use a breather on the rear valve cover, and in the front valve cover run a factory pcv valve. run that to a catch can with a check valve, and hook the other end back up to the intake where the factory pcv would get its signal from. works excellent!

[The_Raven]

The PCV valve side is essentiall left alone. The Valve is left in the valve cover (rear valve cover on genII, front valve cover on genIII), and is left attached to the intake manifold. This will open the valve only when there is high vacuum in the intake, such as at idle or part throttle cruise, and close when at WOT, or in the case of a force fed engine, when there is positive manifold pressure, just like the factory system works. The only change is where the other side of the PCV system is attached. It will remain attached to the opposite valve cover, but instead of being connected to teh intake tube, just before the TB, you move that connection to before the turbo. You can, if you wish to waste money (IMO), add an oil catch tank/can in this hose that is attached before the turbo.

This will keep the PCV system working as it should to remove crank case gasses, and also pull a bit of vacuum to the crank case to help with efficiancy, both at cruise, when the PCV valve is open, and WOT, when the turbo is spooled should pull a bit of vacuum at that point.

The PCV system essentially reverses it's flow between closed throttle conditions and open throttle conditions. This is what the OEM had in mind for this system to work.

You can change the PCV valve itself for a different valve that closes completly when there is pressure applied on the plenum side of the PCV valve. I haven't had a problem with the 660 PCV valve closing under the correct conditions, but it's a good idea to check. Simply blowing into the PCV valve and checking to see that no air is coming out of the crankcase side is an easy test.

So to re-cap, all you need to do is move one connection for the PCV system to function correctly, move the connection from just before the TB, to before the turbo charger inlet. This will also keep the SMOG police at bay too. No open element filters this way and the PCV system stays working the way the OEM had intended it to work.

[3400-95-Modified]

Technically the stock PCV systems connect just after the TB on the VAC side of things.

Owning a stock turbo setup I see they have the good holding PCV valve between the crankcase and a tube going to after the throttle body so when under boost that PCV stays closed, but then they also have a hose running directly to the inlet before the turbo, but also before the regular breather tubes themselves as well...

Best way I can describe the Subaru setup is with a picture so here it is,

Under VAC


Under Boost


Hope that helps describe how a factory setup is. Obviously you don't need to do it the same way. A few think the line that connects between the inlet and the crankcase thats T'd from the PCV defeats the whole purpose of the system since when under VAC it can pull air directly from the inlet, and doesn't have to pull it from the crankcase... which is a possibility.

[3400beretta]

The PCV valve side is essentiall left alone. The Valve is left in the valve cover (rear valve cover on genII, front valve cover on genIII), and is left attached to the intake manifold. This will open the valve only when there is high vacuum in the intake, such as at idle or part throttle cruise, and close when at WOT, or in the case of a force fed engine, when there is positive manifold pressure, just like the factory system works. The only change is where the other side of the PCV system is attached. It will remain attached to the opposite valve cover, but instead of being connected to teh intake tube, just before the TB, you move that connection to before the turbo. You can, if you wish to waste money (IMO), add an oil catch tank/can in this hose that is attached before the turbo.

This will keep the PCV system working as it should to remove crank case gasses, and also pull a bit of vacuum to the crank case to help with efficiancy, both at cruise, when the PCV valve is open, and WOT, when the turbo is spooled should pull a bit of vacuum at that point.

The PCV system essentially reverses it's flow between closed throttle conditions and open throttle conditions. This is what the OEM had in mind for this system to work.

You can change the PCV valve itself for a different valve that closes completly when there is pressure applied on the plenum side of the PCV valve. I haven't had a problem with the 660 PCV valve closing under the correct conditions, but it's a good idea to check. Simply blowing into the PCV valve and checking to see that no air is coming out of the crankcase side is an easy test.

So to re-cap, all you need to do is move one connection for the PCV system to function correctly, move the connection from just before the TB, to before the turbo charger inlet. This will also keep the SMOG police at bay too. No open element filters this way and the PCV system stays working the way the OEM had intended it to work.

Both of my 3500 PCV valves do NOT seal properly under any amount of boost. I can blow through them just by putting them up to my mouth. I'm going to install a check valve inline with my pcv valve.

[The_Raven]

The PCV valve is supposed to be a check valve. Odd that your 3500 PCVs don't seal up when pressure is applied. Just to verify you are blowing into the end where the tube to the intake would be connected, correct?

I can see from the Subaru diagrams above why they have so many oil leakage problems, if that is indeed how they are connected. With the system set-up as laid out above, there will not be any vacuum created in the crank case, at idle. The PCV valve would just be another way to let air into the engine, through the connection to the intake tube.

[92cavquest]

This is a rear mounted turbo setup. Where exactly should I plumb the rear valve cover to on my 3500? "Just before the turbo" is a good 6 feet away.

[The_Raven]

I would still run it to before the turbo. I would likely use some hard tube for the longets parts, and then just rubber hose to attach it at either end.

The reason you want it before the turbo is that under boost, it should be pulling some vacuum through this tube. This helps the engine to keep from blowing out gaskets and if there is enough vacuum created can help create more power, than if the crankcase was just vented to atmosphere or plumbed in after the turbo and a check valve used.