How does the FA20 PCV system work?

[86fun]

I'm confused why there are two PCV ports on the block(s). Can someone explain why?


One is on the right half and one on the left half. The passenger side port goes to the intake manifold after the throttle body. The drivers side port is plumbed into the intake before the throttle body. Why are there two? and why would they vent back to the intake differently? Isn't the case a single space cavity inside the two block halves? I'm guessing there is a difference between the two, why else would they vent differently. Why is this?


I put this in the forced induction area because I want to understand how the PCV system works so that I can fully understand the implications of different kinds of forced induction will have on it (turbo, roots SC, centrifugal SC).

[Irace86.2.0]

http://www.ft86club.com/forums/showthread.php?t=103674

Both of these vent pressure. The rear vents more or is more directly connected to the block. That one has a check valve because of where it recirculates gases to and where it comes from.

All FI applications will increase blowby gases. Managing that excess blowby gases can be done with a catch can that is vented to atmosphere or one that is closed, which may be necessary for emissions. You could not do catch cans and just upgrade your PCV valve to a WRX one from a FA20DIT motor, but you will likely see more crap collecting in the intake.

[Trust86]

The side connected to the intake tube is is the “intake” side of the pcv system, sucks in clean, filtered air. The rear that connects to the intake manifold is the “exhaust” side which recirculates the blow by back into the engine. When you go FI, the stock pcv cant handle the excess air and blow by will “burp” out the intake side of the pcv system (the side that connects to the intake tube). I personally run an open fitting that is also bigger, in the rear side and vta on both sides. No problems.

[Irace86.2.0]

The only issue with Trust86’s setup, besides emissions compliance, is some would prefer to keep a check valve, so under boost the pressurized manifold isn’t pushing against a pressurized crankcase. The car will see much more vacuum than boost, even on track, so it may not matter, but it is something to consider.

[Trust86]

The manifold is capped off, not even connected to the open fitting

[Irace86.2.0]

Originally Posted by Trust86

The manifold is capped off, not even connected to the open fitting

My bad. I didn't read careful enough.

[86fun]

Thanks for the replies guys.


What is the chance that the Edelbrock roots SC could either get unmetered air in the system or have it escape the system via the PCV's causing incorrect fueling? Someone with the stumbling issue I have with mine said they used check valves and catch cans on the PCV's and it resolved the stumbling issue. I'm curious what I should do exactly as I don't want to use catch cans or vent to atmosphere.

[Irace86.2.0]

Originally Posted by 86fun

Thanks for the replies guys.


What is the chance that the Edelbrock roots SC could either get unmetered air in the system or have it escape the system via the PCV's causing incorrect fueling? Someone with the stumbling issue I have with mine said they used check valves and catch cans on the PCV's and it resolved the stumbling issue. I'm curious what I should do exactly as I don't want to use catch cans or vent to atmosphere.

I have a Harrop kit, and all the PCV and vacuum lines are routed pre-blower so those ports never see boost, so a check valve isn’t necessary, nor is it necessary to upgrade to the WRX FA20 PCV valve, but I did anyways. I don’t know what Edelbrock does.

I had a plastic connector break which made for a poor idle and poor performance overall, but much more noticeable at low speeds. I replaced it with a brass connector, and everything was fixed. I also had my direct injector seals that needed replacing, so I was working on that when I found the big leak.

[86fun]

One of the PCV hoses on the Edelbrock kit actually back into the intake after the MAF (but before the blower), and so could possibly alter the air fuel ratio outside of the computers control.

[Fullcoverage]

Did you ever figure out your problem? I have the same issue did you do anything to the pcv system?

Originally Posted by 86fun

One of the PCV hoses on the Edelbrock kit actually back into the intake after the MAF (but before the blower), and so could possibly alter the air fuel ratio outside of the computers control.

[toast]

I don't see how a check valve on the PCV side fixes anything. What kind of stumbling are you talking about? You have logs?