Another Catch Can Thread
 

I did some searching. I came across opinions on setups, on different manufacture's offerings, etc, but I didn't find what I needed or didn't search enough.

I'll be running a Harrop SC with their CARB tune when it is released. I've been told to buy the WRX FA20DIT PCV valve, and I plan on running a PCV catch can, but not a dual catch can. I just doubt it is necessary, as I am not a track junky. My limitations are that I can't run an open system, not with putting filters on valves and venting to air, and not with putting filters on catch cans and venting to air. CARB allows for catch can/s to be installed, but the can/s can't modify the emission equipment more than routing a few new hoses, and the can/s need to be a closed system.

I figure I can replace the PCV valve as described above and get a universal catch can to route the hoses and be done with it, but some have said that the WRX PCV valve isn't needed when using a catch can, so I was hoping to get that clarified, and I also wanted opinions on catch can setups for NA vs forced induction. The only difference seems to be people recommending two vs one catch can, but I have seen multiple posts from people saying their catch can for their breather hose gets almost no output, and those are from people putting down some track time, so I am curious if a dual setup is worth the money, and I am curious if the install is different than putting a catch can between the PCV valve and the line running to the intake like on NA applications.

When there is a catch can, it is recommended to install a check valve between the catch can and intake manifold (to block outward air flow from intake manifold). You can leave the stock PCV valve in place in this case. It will not be functional. See boomba check valve.

So you are saying to not switch to the WRX valve? Why was this valve even suggested? Is it because with FI there is more pressure, so the WRX valve is designed around that pressure level? People suggested to switch why?... does it relieve pressure better with a larger opening or does it have a smaller opening to prevent excessive oil blowby through the PCV system?

Because WRX valve is designed for boosted engine and can hold higher pressure inside intake manifold from leaking into crankcase while stock valve starts to leak that boost into crankcase. But crankcase starts ventilating more oil with the air that goes into intake manifold with a boosted engine. When the oil catch can is added to avoid that oil going to intake manifold, it is also better to avoid the boost pressure expanding into catch can before being stopped on the PCV side. That is why adding a check valve between the catch can and intake manifold is better than replacing the PCV valve with WRX valve. Since boost is blocked at the exit of intake manifold, check valve reacts quicker. Hope I didn't make this too complicated :)

Edit: Another benefit is that the oil clogs up the PCV valve mechanism after a while. However, the check valve will experience less oil on the other side of oil catch can.

Is it ok to do both or is it overkill? I mean the items are like $20 a piece, so cost isn’t a factor. Would one completely negate the other or could it be worse to do both than just one? Thanks.

I think it should be okay to do both but it is unnecessary in my opinion. I wasn't going to mention but I installed WRX PCV valve like a check valve between the intake manifold and catch can. I just pushed the screw end into the hose and tightened with a clamp, it is working just fine like a check valve.

I was thinking of mounting the catch can to the rear engine brace. Anybody know of a good pipe-style mount that would work for like a Mishimoto catch can?

Hold up!!!
On a WRX the manifold is pressurised, obviously. However I would check the Harrop and the setup for the breathers. Most of the PD blowers put the PCV lines on the vacuum side of the blower (pre-compressor) which means that no change in valve is required as you're not pressurising the system. This is the way it is on the Sprintex.

The guy I’m buying my Harrop SC from said he never did the WRX PCV valve swap, but he said it was suggested, I believe by Neil at the Racers Line, but he was unsure about how a catch can would effect things. Would retaining higher pressures effect boost, power or be risky on the engine such that the WRX PCV valve relieves more pressure?

From my understanding is the WRX PCV had a check valve to prevent manifold pressure pressurising the crank case. If your blower connections on are pre-compressor then they will be in vacuum and there is no difference to how it is NA. @mrg666 runs a centrifugal system where the OEM intake manifold is used so when in boost the PCV hoses are pressurised from the supercharger. I would suggest that the Harrop is like the Sprintex, it'll be obvious as the brake booster line will be connected to the same location.

WRX PCV valve and our stock PCV valve have the same functionality and fit. The difference should be the higher pressure that WRX PCV valve can hold up. This is my understanding.

I don't know about the Harrop system. But one thing is obvious (at least to me) that the compressor (centrifugal or screw) is pressurizing the intake manifold. The crankcase should not be connected to the intake manifold without a check valve. And if there is a catch can, the check valve should be on the hose connecting the catch can to intake manifold.

If Harrop has a built-in check valve on the port connecting to crankcase, if this is what you mean, that I can understand. In that case, I agree, no additional check valve or WRX PCV valve replacement needed.

What he was getting at is the Harrop connects to the stock PCV on the vacuum side of the supercharger (throttle body most likely), so there is no difference from stock and you don't need a check valve.

Correct, but pre-compressor will always be in vacuum. Only post compressor sees positive pressure. Reading the Harrrop installation instructions you have one breather on the intake and the other on the compressor housing. These should both be pre-compressor and thus on the vacuum side of the manifold.

Yep, figured that out after the previous post. Thanks!