Thread: Installing an oil catch can on ve

If you're doing that, don't forget the factory restrictor. It is inside the OEM hose, in the middle somewhere hidden.

oh really? What exactly is it for? I still have the hose sitting in my garage since i just used the lines that were supplied with the catch can

I'm not 100% sure on what the two restrictors are for, but I have a few educated guesses. I think it is a combination of all of these.

The small PCV side restrictor:
1) Prevents too much vacuum being placed on the crank case. (The engine is a very strong air pump.)
2) Prevents too much air ingestion which would cause the idle to be aggressive. (Air coming in through the PCV valve is additional to the normal idle air.)
3) Suddenly speeds the air which aids in oil separation.

The WOT section restrictor:
1) Allows vacuum creation in the crank case. (Without this restrictor, there is no way for the engine to create any real vacuum in the crank case.)
2) Prevents too much air ingestion which would cause the idle to be aggressive. (Air coming in through the WOT section is additional to the normal idle air.)
3) Suddenly speeds the air which aids in oil separation.

So there are 2 restrictors in the line or just the one which serves multiple purposes. My idle didn't change at all. Even though i was having some troubles getting the idle to stay at 850-900 before the install.

There are two restrictors total in the entire positive crank case ventilation system. One in the "PCV" hose that you've just replaced (sorry if my diagrams don't show that yet), and one in the wide-open-throttle section that is clearly labeled in my diagrams.