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Bypass the PCV?

You guys still aren't getting the fact that I would not be running the PVC into the intake! If the PVC isn't hooked to the intake then it wouldn't be metered air. Is there some magical way that metered air is getting into the crank case other than the PCV and the valve cover vents because those components would no longer be hooked to any source of metered air.

As far as the track I'm only looking into this setup at the moment. I don't actually have it hooked up this way and I never track my car anyway. I know FastCougar plans to run it to his exhaust though.
 
Air goes into the engine... it goes by the rings, and magically.. poof, it's in the crankcase and valve covers.

The intake has a vacuum anyway... so air only goes from the crank and valve covers into the intake... never the other way. If air is going into the crankcase from the intake then you PCV valve is bad.

I think you need to take a look at how the system works.
 
The amount of air getting by the pistons is negligible. You'd loose a significant amount of power otherwise during the compression cycle. I know how the "system" works.

Currently I vent my valve cover breathers and have the PCV running to the intake as it would normally. I don't have any lean or rich conditions from metered air moving in or out of the system. It sounds like people are recommending a stronger PCV valve for FI applications so I'll look into that along with checking my current valve to see if there are any leaks.
 
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Blackcoog said:
The amount of air getting by the pistons is negligible. You'd loose a significant amount of power otherwise during the compression cycle. I know how the "system" works.
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So get rid of the PCV all together and just seal up the crankcase... it's just a negligible amount of air in there anyway.
 
Right, because I forgot that myself and Rara already told him how to correct the problem and with 2 different options of doing it.
 
I'd just like to add.

If you have valve cover breathers to atmosphere the PCV should not return to the intake. You're adding unmetered air to the system.

Saying that, if you run valve cover breathers you need another way to evac the crank better than to atmosphere. I'd just a vacuum pump myself.

And it could be that your engine will be fine with the air lost to blowby especially since the engine will compensate for a pretty good amount of air variation from the MAF signal with long and short term trimming (in closed loop) and you can tune the WOT with a wideband and blah blah blah.

I however like to keep all my air where it is supposed to be.

In which case you need your valve cover breathers hooked up to a "Non-Pressurized" source of metered air and you want the PCV return hook back up to the intake. In this instance you have 2 options. Post or pre Turbo. I myself prefer the pre-turbo route because it will have a vacuum on it even under WOT and you don't need a PCV valve that will seal against pressure. Note that if you do this method you will want to insure that you have an air/oil seperator in place to prevent contamination of the air intake and cause possible compressor erosion.

Option #2 is to keep the pcv where it is and use a pcv valve that will seal against pressure.

There, that was my helpful post for the day.
 
Barge said:
There, that was my helpful post for the day.
Click to expand...

Sure was! Thanks, Barge!

The other day I discovered oil has been spraying out my BOV, which means that oil has been drawn out of the valve-cover-breather lines and run all the way through the induction system to the throttle body. :eek: The obvious fix here is an oil separator or catch can. Seems like a pint-sized can would be sufficient. Some guys are attaching small, air filters to their catch cans, but this is not emission-friendly and would seem to allow air into the system that was not metered by the MAF. One cheap yet attractive option is the Greddy/Megan catch can, but these twin cans by Saikou Michi sure look sweet!

With the PCV system on my mind, I was wondering what should be done about the valve. The more I learned about it, the more I understood that its stock connections were not meant for boosted applications.

In a normally-aspirated system, the valve is held open by the vacuum present in the intake manifold. The valve is open so long as the pressure inside the crankcase is greater than the pressure outside the crankcase.

In a forced-induction system, the vacuum inside the intake manifold would steadily decrease as the turbo spooled. Under full boost, the intake manifold would become pressurized and force the PCV valve to remain shut, trapping the oil vapor (a.k.a. blow-by). Of even greater concern is the possibility that the "one-way" PCV valve could be forced open under boost and allow the crankcase - the volume underneath the pistons - to become pressurized, which could cause seals to leak as well as hurt performance.

So if we cannot keep the PCV valve connected to the intake manifold, then the question becomes: to what should we connect the PCV valve? Someone tried each option on a Honda. Some guys are venting the valve to atmosphere by simply running a piece of tube under the car. Others, are venting into the exhaust stream. In each case, the hope is that there is enough vacuum to open the PCV valve and allow the blow-by to escape. Each of these options, as stated before, are unacceptable for track use, not to mention emissions. :troutslap:

In conclusion, if the system must remain closed, then the PCV valve, along with the valve-cover breathers, should be vented into the intake after the MAF but ahead of the turbo- or super-charger. BUT WAIT... that Saikou Michi guy says this:

Saikou Michi said:
Q:Why not join the breather and the PCV line into 1 can?

A: The simplest way to explain it is this... The PCV system works in ONE direction. Under vacuum the flow comes from the valve cover through the PCV valve and into the intake manifold, during this time, the air that is being sucked out is being replaced by the air coming in through the breather hose. Air comes in, and air goes out through the PCV line. When 2 lines go into 1 can, there is NO VACUUM effect possible.
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So, two cans are needed because two pathways are needed. If two pathways are needed, can both the PCV valve line and the valve-cover lines be inserted just ahead of the compressor?

Regardless, is there enough vacuum in the intake to sufficiently open the PCV valve? Manifold vacuum is -20 according to my boost gauge. I don't think the intake will create that much, at least, not before the compressor is spooled.

My final question is the same one poised by BlackCoog: Where does that other EVAP line go that is connected to the PCV valve? :help:
 
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you would have to use 2 seperate catch cans. one for the valve cover breathers and one for the PCV valve. from the catch cans both lines can then (and IMO should) go into the intake tract before the turbo.
 
Not to get sidetracked, but I came across another interesting idea. This guy suggests using vacuum from the intake manifold when not under boost, then using vacuum from the compressor when in boost.
 
That's basically what the stock WRX does.

Intake Manifold under vacuum. Pre-turbo during boost.

I'd hook up your boost/vac gauge pre-turbo to see how much vacuum it pulls. I keep meaning to do it on my car because I'd like to know.

Also you want to keep your vacuum side and your valve cover line side seperate from each other at different spots on the inlet to the turbo.

You want what was the PCV line... the line that will be sucking... to be connected close to the compressor inlet. Then you want your valve cover line a good 6-8" farther towards the air filter.

This way you should have a higher vacuum on the "PCV" line than the valve cover line.

Ideally you should not need an air/oil seperator on the valve cover line because air should be flowing into the valve covers, not out of them. However, chances are you'll get some back flow in it at times and some oil so you might as well put one in.

Theoretically with the above setup you should never really need a PCV valve since it will always be under vacuum but it wouldn't hurt to use one anyway.
 
Thanks again, Barge!

I was thinking that if separate pathways are required from the valve and breathers to the cans, then separate pathways would be required from the cans to the intake as well for the same reason. I agree that it would be wise to check the vacuum/pressure at the sites I am thinking of tapping on the intake. If it should read significantly less than the manifold vacuum, and there is concern about whether the PCV valve will open sufficiently, then I'll want to draw vacuum from multiple sources, as in a stock WRX.
 
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Livinsvt said:
plus a good sealing pcv is all you need. 1500 Miles on boost and not a single ounce of oil is anywere to be found in my intake or I/C.
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Is your PCV rerouted to the intake, along with the breather lines? Did you upgrade the PCV valve or are you using the stock spec?
 
Yes, everything is routed back to the intake like it should be. I have a seperate smaller seperator on the valve covers. Actualy thinking of removing it, there is not a drop of oil anywere in it. I am using an upgraded pcv valve. I believe from a older Cobra. Its ridiculous how clean my intake is. Plus with every thing else thats changed the car idles like stock. :cool:
 
what about possibly swappin to 04 valve covers with the updated pcv system? the pcv was mounted into the valve cover and the center block breather was blocked. then u could use the stronger pcv valve ? idea. just thinking out loud
 
fordrule said:
what about possibly swappin to 04 valve covers with the updated pcv system? the pcv was mounted into the valve cover and the center block breather was blocked. then u could use the stronger pcv valve ? idea. just thinking out loud
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i hear ya, but i don't know what advantage there would be to relocating the PCV valve itself. either way, i need to reroute it away from the intake manifold, at least while under boost.
 
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