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Bypass the PCV?

S

SoopaCooga

Veteran CEG'er
Joined
Jun 19, 2001
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Location
Fairfax, VA
I have attached an article found by Blackcoog that argues in favor of bypassing the PCV system for 99+ Ford engines which suffer from oil vapor blowby being recirculated into the intake. Why haven't I come across anybody here with a turbo having to modify their PCV system?

PCV Bypass said:
Lets talk about supercharged or turbo applications. We think the dual vent system is the way to go in any
high boost or blowby application because the general flow requirements through the PCV system are restricted
by the small size of the lines and the small aperatures of the vent and PCV valve. This is especially
critical on the 99-up models which already have PCV systems which may be seriously diluting the air/fuel octane
with oil vapor.

The drawback to venting an engine’s blowby is that the breathers will eventually become oily and start to drip.
The answer is not pretty but it is effective. Periodically remove the breathers, wash them in solvent or K&N
filter cleaner to remove the oil, reinstal them, and wipe off your valvecovers.
Click to expand...
 

Attachments

  • PCVBypass.pdf
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There is an oil seperator bolted to the block between the heads, a line comes out of the seperator and goes to the PCV valve, the line is split with one end going into the intake manifold and another line going to the firewall. Each valve cover has a vent which is normally run into the intake for NA engines. I'm not sure what the function is of the line that goes to the firewall.
 
My current setup runs the valve cover vents to a breather. When the intake manifold is under vacuum or there is positive pressure in the crank case the valve will be open allowing air into the intake from the crank case. This allows un-metered air into the system. At the moment this hasn't been a major issue but I do have somewhat of a rough idle I'd like to clean up and I think this could be the cause.

The article above states to remove the PCV valve and run the evap canister purge vent to a vacuum line. Is the evap canister perg vent the short tube that normally plugs into the intake from the PCV valve or is it the plastic line that goes to the firewall?
 
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Are people with FI Moving the PCV hose to the inlet size of the turbo? Along with the valve cover breathers?
 
Barge said:
Are people with FI Moving the PCV hose to the inlet size of the turbo? Along with the valve cover breathers?
Click to expand...
i just have the valve cover breathers on the inlet side of the turbo but i was thinking about moving the PCV valve to the inlet side as well. not only would you not have to worry about pressurizing the crankcase but there will always be some amount of vacuum in the line when the throttle is open.

Edit: both PCV and VCV lines have their own oil seperators in line as well.
 
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Yeah, any vent lines should be located between the MAF and the turbo. Besides not pressurizing you will also have a pretty good vacuum in this area at WOT.
 
Ahh, that stinks. I guess that would be a potential downfall to that.

Not having a vacuum on the crankcase and valve cover breather has got to be costing you some power.
 
Switch the PCV valve itself to one designed for use in a boosted application. The one for the 2.3L turbo T-bird is one that is really common for "homebrew" type setups.

When working properly, the pcv should NEVER allow air to flow from the intake tract into the crankcase, only out from the crankcase. Anyway, the stock valve was never designed to handle the positive intake pressure, so they often fail and allow air to flow the wrong way.
 
Chris ... I'm not sure what the best way to go about this with a blow through application would be. Ideally, you want the vacuum source for the PCV to be somewhat constant and to never see boost. That being said and with your setup the way it is, I seriously suggest you get a constant vacuum on the PCV and stop boosting it ... go the "exhaust slash-cut" setup that you asked me about in my thread on NECO.

Keep in mind that boosting the crankcase should NEVER happen simply because you are adding more resistance to the crank AND increasing blowby ... both bad for power ... combined, I would care to say that you are loosing a good 3-6% of your power potential! Thus the recommendations here to use a boost application PCV valve since in theory, acts more like a one-way checkvalve. My advice, if you keep the setup the way it is now, add a one-way check-valve inline with the PCV and keep using the existing PCV. However, my advice is to get a constant vacuum on the PCV system. There are reasons that drag/circle track cars use very expensive vacuum pumps on the crankcase ... it frees up quite a bit of horsepower!
 
Using a technique in an article posted over on NECO you can weld a tube on the exhaust after the O2's at a 45 degree angle and it will create a vacuum when the air rushes past. You could also do this on an intake pipe but then you could suck oil into the engine. Sucking it into the exhaust is safer.
 
Right, but it's still a leak of metered air. Granted you could probably adjust for it, but it's still there.

You can also use a GM air pump that was used on some corvette's and some other cars I believe. Fairly affordable way to do it.

I believe that doing the exhaust method is illegal in some places for use at tracks and drag strips because it can lead to oiling down the track.
 
How would it be leaking metered air? The vacuum source will be the exhaust and that isn't metered air. The valve covers will have breathers on them. It will completely separate from the intake tract.
 
Blackcoog said:
How would it be leaking metered air? The vacuum source will be the exhaust and that isn't metered air. The valve covers will have breathers on them. It will completely separate from the intake tract.
Click to expand...

The air in the valve covers is metered air, as is the PCV air.
 
I still don't see how is it metered If you route the PCV which normally goes to the intake manifold to a different vacuum source that isn't metered and the valve cover vents are vented via breathers then it can't be metered. The crank case air would be seperate from the metered intake air.
 
Blackcoog said:
Using a technique in an article posted over on NECO you can weld a tube on the exhaust after the O2's at a 45 degree angle and it will create a vacuum when the air rushes past. You could also do this on an intake pipe but then you could suck oil into the engine. Sucking it into the exhaust is safer.
Click to expand...

Basically what barge said. This is a big no-no at most any track since you will eventually spit oil out onto the track out the tailpipes. In fact, in most road racing classes, you will get black flagged during a race if you are dropping any oil on the track.

Blackcoog said:
How would it be leaking metered air? The vacuum source will be the exhaust and that isn't metered air. The valve covers will have breathers on them. It will completely separate from the intake tract.
Click to expand...

Where do you think the air comes from that you are drawing into the PCV system? EVERY bit of air going in is metered on these engines, even the valve cover breather air and the blowby that both contribute to the air drawn back in by the PCV system. If you are custom tuning on a speed density setup, and compensate for it, fine, but MAF systems really need to stay closed so that the ECU can stay on top of what is going on.

The right answer is a PCV valve designed to handle boost. It really isn't that hard people. I don't think some of you realize how much vacuum is really drawn on the PCV system whenever the throttle body is closed, even for a second.
 
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