Turbo + open PCV = fail?

Well, I had an interesting evening.

When i bought the MX6, i understood that the turbo would need to be rebuilt/replaced sometime in the future, but i figured i'd have some time on it, after all, it ran fine, smoked very little, etc....

So much for that. Last night, after painting for my buddy, it wouldn't hit positive pressure at all, and i couldn't even hear it spinning. After i started to smell oil, and seeing puffs come out the exhaust between shifts and on decel, i pulled into a gas station. Car still running fine, other than being dog slow.

Pulled the intake off, turbo is shot. So much shaft play that the wheel was stopping itself on the housing. Ok, i can live with that. Limped it home trying to keep it at 20lbs of vaccuum.

Called around, sourced another of the same turbo, went and picked it up for $60. In perfect shape.

That's the good part! I can live with $60 for a polished Supra turbo.

Now. The guy i got the turbo off of owns an import performance shop, specializing in Supras, 3000GTs, and the like. So.... high HP boosted cars. I noticed that he had his PCV plumbed back into the intake tract right before the turbo on his 700+whp MKiii Supra. So, i asked him about it, saying that mine was just vented to atmosphere. He immediately went on a rant that it's bad to do that, because there has to be some sort of vaccuum going on for the system to work properly, and that it possibly may have contributed to the death of my turbo.

So here's my question, since i don't anticipate getting a straight answer from the MX6 forums.

Is it bad to run a turbo 4-banger with the PCV vented to atmosphere or a tube running to a bottle? Is it advisable to run it back into my intake tract? It doesn't seem to be dripping or blowing a whole lot of oil everywhere, and it runs great. I just don't want to make a habit of blowing up turbos, and if putting it back through the intake is a good thing, then i'll do it.

I appreciatchya'all!

I used a PVC valve vented to a catch can that was in turn vented to the intake via a second PVC valve (so that it would not pressurize the can with boost.

He's an idiot. Run a hose from your PCV to a catch can. I like the plastic Summit ones (NHRA legal) with a vented top and a drainback. The PCV on 2.3's comes from the block so I set it up with another hose/valve from the valve cover as well.

Oil particulates onto a spinning compressor wheel = shortened life and less performance.

P71 wrote: He's an idiot. Run a hose from your PCV to a catch can. I like the plastic Summit ones (NHRA legal) with a vented top and a drainback. The PCV on 2.3's comes from the block so I set it up with another hose/valve from the valve cover as well. Oil particulates onto a spinning compressor wheel = shortened life and less performance.

Ok, so just a one way hose into the can, call it good? I'll probably rig up a temp solution tonite when i replace the turbo, then.

I don't have a PCV from the block, valve cover only.

I like John Brown's solution the most, I think the factory PCV routing runs from the valve in the valve cover and then over to a fitting on the rubber intake ducting before the throttle body. But I like the idea of the catch can and the second PCV valve. However, I would try to replicate the factory PCV setup exactly since it seems to be a reliable system, if you can.

There should be two vents, no? The one with the actual PCV valve goes into the intake manifold, where it can see vacuum. There's that taken care of.

The other is usually an inlet unless you have a failed valve or a blow-by problem. That one should be plumbed into the intake system between the air flow meter and the turbo - it shouldn't see boost.

If you vent it to atmosphere on a system that uses a mass airflow sensor or an air flow meter (as opposed to a MAP) then you'll be sucking in unmetered air causing mixture problems.

Does the vacuum hose diagram on the bottom of the hood include the PCV system? I forget.

It should.

Keith wrote: There should be two vents, no? The one with the actual PCV valve goes into the intake manifold, where it can see vacuum. There's that taken care of. The other is usually an inlet unless you have a failed valve or a blow-by problem. That one should be plumbed into the intake system between the air flow meter and the turbo - it shouldn't see boost. If you vent it to atmosphere on a system that uses a mass airflow sensor or an air flow meter (as opposed to a MAP) then you'll be sucking in unmetered air causing mixture problems. Does the vacuum hose diagram on the bottom of the hood include the PCV system? I forget.

I've really only poked around enough to know that the hose coming off the valve cover is a PCV vent. I'm not sure if the vaccuum hose diagram includes it or if it's even there to be honest with you.

There is a SMALL amount of oil residue in the tube coming off the valve cover. General consensus is that it's normal, because the PCV system isn't all that great on these cars to begin with.

I assume (makes ass of u and me!!) that the one going into the intake manifold if it exists is fine. Like i said, the car runs great, no stumbling, i'm not getting any weird vaccuum readings, it sits rock solid at 25lbs vaccuum at idle.

I guess i'll have to do more research. I do know for a fact that i do not have any lines going into the intake tract, anywhere. Is there a good reason to actually have it there? Or will the one way catch can idea be fine?

From CARS

I couldn't find a photo but here is a stick drawing to help

On a turbo car, you're going to want some sort of one-way valve on that thing so you don't pressurize your valve cover - I'm assuming that the valve cover on the left. Better to plumb it back into the intake pre-turbo.

Sorry, the I didn't save the last drawing, it was marked as the larger ports being Ford turbo style PCV valves, which offer great blow back protection one way.

From CARS

Keith wrote: On a turbo car, you're going to want some sort of one-way valve on that thing so you don't pressurize your valve cover - I'm assuming that the valve cover on the left. Better to plumb it back into the intake pre-turbo.

I apologize for seeming like i'm wasting anyone's time.... but i'm getting confused now with all the answers.

Is it HURTING anything besides making a slight mess that needs to be cleaned every week or so, having the hose coming off the valve cover just open like that?

What are the benefits to running it back into the intake?

Is it simply just a mess issue with it venting the way it is now?

I'd just like to take the oppurtunity to say that i love you guys.

I posted the same thing on the MX6 forums, and they're telling me that i shouldn't be running the line off the intake manifold open to atmosphere because it'll pull in unmetered air.

I felt a family of brain cells die through the force.

PCV systems are pretty poorly understood. I've seem some really odd "solutions" from tuner shops. And I fully acknowledge that I'm probably going to make some mistake in this post - I usually have Bill to lean on for the fundamentals on this sort of thing. So go ahead and point it out

But basically, you have to control your pressures. You don't want to pump boost into your valve cover, because that will blow oily air out the other side. Let's start with a naturally aspirated car first because that's a simpler setup.

There are two fittings on the valve cover. One has a PCV valve and is hooked to the intake manifold. Not to the intake plumbing before the throttle body, but where it's going to see vacuum. This allows the gases in the crank case to get pulled into the intake manifold, where they're burned up in the engine.

The other fitting is a vent. If the intake is sucking a lot of gases out from under the valve cover, the vent lets more air in. Under these conditions, some of your intake air is thus coming through the vent. That's why it needs to be plumbed back into the intake piping so the air is metered. If you have a car that runs off a MAP sensor, that's not critital.

Under some conditions and depending on the amount of blow-by, the vent can be an outlet. That's when you see your mess, and that's the purpose of the catch can - to pull the oil out of this air before it goes back into the intake system.

Now, add a turbo. You really don't want to dump boost into the valve cover and crankcase. So this means you need a PCV valve that can deal with boost, and the vent has to be connected pre-turbo where there's no boost.

Here's the basic thing: on a factory turbo car, you're not really going to improve on the PCV system unless you're simply adding a catch can. Putting a filter on the valve cover and letting it vent to atmosphere looks cool because it's race, yo and it's easier to plumb in when you're making your own home-brew intake system. But there's no benefit otherwise.

That you love us? Or the intake manifold part? The one that goes to the intake manifold is connected correctly.

I think i see what you're saying though. I will see if i can get a nipple welded on my intake and go from there. Thanks!

Is there any reason you can't just rebuild the PCV system to be exactly as it left the factory? You mentioned hearing somewhere that it wasn't a very good system, but I'm not sure what it does poorly. The factory IHI turbo lasted a good 180,000 on my Mazda so in my personal experience, longevity didn't seem to be hurt by the system as it came from Mazda. Hell, I never even changed the PCV valve itself, just made sure it would rattle when removed and shaken.

Keith wrote: PCV systems are pretty poorly understood. I've seem some really odd "solutions" from tuner shops. And I fully acknowledge that I'm probably going to make some mistake in this post - I usually have Bill to lean on for the fundamentals on this sort of thing. So go ahead and point it out But basically, you have to control your pressures. You don't want to pump boost into your valve cover, because that will blow oily air out the other side. Let's start with a naturally aspirated car first because that's a simpler setup. There are two fittings on the valve cover. One has a PCV valve and is hooked to the intake manifold. Not to the intake plumbing before the throttle body, but where it's going to see vacuum. This allows the gases in the crank case to get pulled into the intake manifold, where they're burned up in the engine. The other fitting is a vent. If the intake is sucking a lot of gases out from under the valve cover, the vent lets more air in. Under these conditions, some of your intake air is thus coming through the vent. That's why it needs to be plumbed back into the intake piping so the air is metered. If you have a car that runs off a MAP sensor, that's not critital. Under some conditions and depending on the amount of blow-by, the vent can be an outlet. That's when you see your mess, and that's the purpose of the catch can - to pull the oil out of this air before it goes back into the intake system. Now, add a turbo. You really don't want to dump boost into the valve cover and crankcase. So this means you need a PCV valve that can deal with boost, and the vent has to be connected pre-turbo where there's no boost. Here's the basic thing: on a factory turbo car, you're not really going to improve on the PCV system unless you're simply adding a catch can. Putting a filter on the valve cover and letting it vent to atmosphere looks cool because it's race, yo and it's easier to plumb in when you're making your own home-brew intake system. But there's no benefit otherwise.

I must say my drawing is suspect... here is another representation that better illustrates the system. I will correct mine to show the same.

pres589 wrote: Is there any reason you can't just rebuild the PCV system to be exactly as it left the factory? You mentioned hearing somewhere that it wasn't a very good system, but I'm not sure what it does poorly. The factory IHI turbo lasted a good 180,000 on my Mazda so in my personal experience, longevity didn't seem to be hurt by the system as it came from Mazda. Hell, I never even changed the PCV valve itself, just made sure it would rattle when removed and shaken.

That's the problem.... i have no idea how it was set up from factory, and my turbo setup is quite different from factory. I'm worried about having enough space to plumb the breather from the valve cover back into the intake. There's only about 2-3" between the VAF and the turbo, and i'd have to go over the exhaust manifold to do it if i want even a remotely direct route.

I guess it doesn't REALLY matter how long it is... i could run it around the battery and go through that way, avoiding heat.

As for what it does poorly, is hold up to non-stock conditions. That's at least according to mx6.com. Which.... i'm starting to just think i won't even bother there anymore, since they couldn't realize i was talking about the hose off the valve cover, which here, i was educated that it's just the breather.

Good diagram, John. Nice and clear. The "Air cleaner" should also be taken to include the mass air flow sensor or air flow meter. Note the position of the throttle butterfly, and a turbocharger should be between the breather hose and the throttle.

93celicaGT2 wrote: As for what it does poorly, is hold up to non-stock conditions. That's at least according to mx6.com. Which.... i'm starting to just think i won't even bother there anymore, since they couldn't realize i was talking about the hose off the valve cover, which here, i was educated that it's just the breather.

The hose running from the valve cover towards the intake does, however, have a check valve in it that rattles just like a PCV valve. I assume that's what it is, I always checked it that way to make sure it was still free internally. Don't run a straight hose to the thing or you'll probably be adding boost pressure to the air space under the valve cover.

I can't speak for MX6.com, I don't think I ever went there, there was some Probe site that I glanced over once a couple years ago that looked okay but not great either. My quest was always transmission info. I wonder if there's a good pictorial and description of the complete PCV system around that you could use to help rebuild the system. Also, I know your turbo itself isn't stock and there had been some other changes but the PCV system really should be the same I would think.

pres589 wrote:

93celicaGT2 wrote: As for what it does poorly, is hold up to non-stock conditions. That's at least according to mx6.com. Which.... i'm starting to just think i won't even bother there anymore, since they couldn't realize i was talking about the hose off the valve cover, which here, i was educated that it's just the breather.

The hose running from the valve cover towards the intake does, however, have a check valve in it that rattles just like a PCV valve. I assume that's what it is, I always checked it that way to make sure it was still free internally. Don't run a straight hose to the thing or you'll probably be adding boost pressure to the air space under the valve cover. I can't speak for MX6.com, I don't think I ever went there, there was some Probe site that I glanced over once a couple years ago that looked okay but not great either. My quest was always transmission info. I wonder if there's a good pictorial and description of the complete PCV system around that you could use to help rebuild the system. Also, I know your turbo itself isn't stock and there had been some other changes but the PCV system really should be the same I would think.

Oh, right. The PCV system is the same, they're just trying to tell me that it doesn't like higher HP situations.

I think the portion of that hose with the valve in it is gone. But if it's just a vent, how would it add pressure under the valve cover?

I'm sorry i'm such a n00b. It's been awhile since i bought a car that really needed much attention like this. It's eye-opening.

You don't want any lines going from the boosted area to the engine/valve cover. No PCV valve survives long in those conditions. If you need vacuum, go pre-turbo, but it's not necessary. If you route it like my diagram there is no reason for any lines in the intake tract at all. The entire PCV setup is now a separate airflow than the air used for the engine, so no metering problems. It also allows you to keep an eye on blow-by, reduce oil consumption (and thus valve and turbo coking), and lengthens turbo life.

Ok... when i say intake tract, i meant actual intake. Pre-turbo. Sorry for all the confusion. I wracked my brain last night trying to figure out why you guys were all making a big deal of running boost directly to the valve cover, when in my mind, i said nothing of the sort.

I got it now.