Catch Can Design Comparison Question

Hey Guys, been a longtime reader of the forums and I have a questions that I haven't been able to find an answer to in all the Catch Can discussions;


What are the pro's and con's (if any) of the two different catch can designs out there with regard to catching off of the intake manifold side of the PVC vs. catching of the air intake side of the PVC?


For example; I notice that APR's Catch Can is catching off the intake manifold side, and conversely ECS Tuning Catch Can and many others on the market are catching off the air intake side, yet they both plug the intake manifold. Does this fundamentally change anything?

I'm not sure that it matters, to be honest. A lot of aftermarket setups use an Africa plate and those eliminate the rearward outlet entirely, leaving only the forward outlet/inlet.
Air flows fairly uniformly out of both ends during OEM operation and by plugging one side or the other, you're still forcing air out of one direction. It shouldn't change anything.

I've personally had issues with catch cans on my cars. I have also seen issues with them on cars at my work.
I'll explain a bit to help.
The Oem pcv will use the intake manifold vacuum at idle and off boost to create suction. When the intake manifold is under pressure or boost the pcv will block that port and use the intake tube side to create suction. This prevents pressure from going into the crankcase and blowing out oil seals. It also keeps vacuum in the crankcase at all times.
When you use any aftermarket pcv that blocks the vacuum port on the intake manifold, you are eliminating vacuum at idle and when off boost cruising. The intake tube port creates nearly zero vacuum while off of boost.
This is bad because you want vacuum at all times in the crankcase, especially with an engine that is prone to blowby gasses such as ours. Vacuum is necessary to remove blowby gasses and to help seal the piston rings as well.
You can cause excessive oil consumption due to oil escaping past the rings into the combustion chamber. You can also cause oil drainage issues on the return line from the turbo due to pressure build up in the crankcase. These issues will vary due to engine wear and quality of oil and will get worst over time. I'm sure many people will back up these companies selling garbage pcvs and catch cans. But at the end of the day, this is the truth. I have a two dragsters in my shop right now, both of them have belt driven vacuum pumps going to the valve covers to remove crankcase gases. If that doesn't tell you how important vacuum is, I don't know what will.

My advice for the best catch can, put a catch can between each line on the system. One between the oil separator and intake manifold, another one between the oil separator and intake tube.
This should ensure proper function and oil separation.

Thanks guys. That's great feedback.



Jiffy, you bring up an interesting point as well that was a concern of mine with regard to the vacuum pressure, but I didn't even think about the idea of putting on two catch can systems. Its a bit of an expensive endeavor, but it seems like it would resolve some of the issues with the OEM PCV without any negative implications. I haven't had any PCV system issues yet (somehow), but I'm trying to anticipate replacement as I'm at 95k miles now.

I would definitely replace the diaphragm in the pcv immediately. They usually fail around 100k and blow the rear main seal.
Here is a good quality one that holds up.
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/233114364631

I have gone back and forth about installing a catch can. I think I'll just replace the OEM PCV at 50k.

Jiffyjetta said:

I would definitely replace the diaphragm in the pcv immediately. They usually fail around 100k and blow the rear main seal.
Here is a good quality one that holds up.
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/233114364631

Click to expand...

Is this an alternative to replacing the whole PCV? I was going to replace mine as a precaution but if all I need is the diaphragm then that would be better.

Jiffyjetta said:

I would definitely replace the diaphragm in the pcv immediately. They usually fail around 100k and blow the rear main seal.
Here is a good quality one that holds up.
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/233114364631

Click to expand...

Thanks for the suggestion. I will replace that sucker asap.

i like to put an external check valve in the intake line they are available to hold 30 psi and open about 1/2 pound of vac. I run 2 seperate cans on my TSI one on each side.

GolNat said:

I have gone back and forth about installing a catch can. I think I'll just replace the OEM PCV at 50k.




Is this an alternative to replacing the whole PCV? I was going to replace mine as a precaution but if all I need is the diaphragm then that would be better.

Click to expand...

I want more information on this as well as i am about to replace my PCV and this would save me a ton of money.

From experience I can tell you that it's a pain the ass replacing the diaphragm. The plastic cover is a bitch to remove without breaking the tabs. I've only tried on two crapped out PCVs out of curiosity though.

leiito said:

From experience I can tell you that it's a pain the ass replacing the diaphragm. The plastic cover is a bitch to remove without breaking the tabs. I've only tried on two crapped out PCVs out of curiosity though.

Click to expand...

The kits come with a new plastic cap and spring. It litterally takes 1 minute to replace.

Tagged, this seems like a very interesting thread

Here is a good comparison between the cheap pcv diaphragms and the quality ones.
As you can see, the thickness of the material is more than double. The thin black one can be torn by hand easily, and the thicker orange one cannot be torn by hand. There are fibers woven into the rubber for strength.
I would recommend using a quality one, either the newest revision OEM, or simply replace the diagram with the link posted above.

I can post a few pictures or a short video of how to pull it apart tomorrow.

I took off my PCV Revision ending in an E. I took off the plastic cover without any tabs breaking and found both the Check valve and diaphragm without any rips. Once i do my catch can ill replace this at the same time. Couldn't hurt.

Thanks for the pics!

Just ordered mine should be here Saturday.