Hey, sorry to bump this thread but it was brought to my attention by someone else on a Nissan forum I frequent more often.
There, I have a
couple threads that try to fully explain the factory PCV system on the SR20 engine and I rate different modifications based on the following criteria resulting in an over-all rating:
- De-clutters the engine bay - Yes/Maybe/Unchanged/No
- Simplifies crank case ventilation system - Yes/Maybe/Unchanged/No
- Maintains stock prevention of crank case pressurization - Yes/Maybe/Unchanged/No
- Stops intercooler from acting as an oil separator - Yes/Maybe/Unchanged/No
- Helps remove more oil from the air - Yes/Maybe/Unchanged/No
- Help evacuate the crank case - Yes/Maybe/Unchanged/No
- Maintains or improves the stock flow capacity - Yes/Maybe/Unchanged/No
- Helps promote ring seal and prevent blow-by - Yes/Maybe/Unchanged/No
- Helps prevent oil smoke in exhaust - Yes/Maybe/Unchanged/No
- Helps prevent dip stick from popping out - Yes/Maybe/Unchanged/No
- Helps prevent oil leaks due to pressure - Yes/Maybe/Unchanged/No
- Helps keep intake track clean including throttle body - Yes/Maybe/Unchanged/No
- Helps keep intake manifold/plenum clean - Yes/Maybe/Unchanged/No
- Maintains or reduces amount of pollutants - Yes/Maybe/Unchanged/No
- Maintains prevention of un-metered air from entering the intake - Yes/Maybe/Unchanged/No
A final verdict is then given.
My point? Well, first off I wanted to congratulate the members in this thread who've figured out the system and how to improve that. That is no small task. Plenty of people make things worse when they start messing with this system. You who have it figured out, you know who you are.
Secondly, I wanted to touch on the PCV valve itself. The most recent posts in this thread mention the valve is quite literally a ball-type check valve. That is not the case. The valve is slightly more advanced than that, and information on it can be found here:
Crank Case Ventilation fully explained. (Naturally aspirated edition.) - SR20 Community Forum - The Dash
And here' Nissan's diagram of it:
http://i160.photobucket.com/albums/t...Inspection.jpg
Thirdly, I wanted to touch on the factory restrictors that exist in the system. I noticed there was some talk about them, and pictures posted. I too was surprised to find both of them. Yes, there are two. One is in the small "PCV hose" that goes to the plenum (pics of this were posted), and the other one is sort of in the factory intake "boot. Here is
a picture of that one.
The reason for these restrictors is hard to fathom, especially the second one in the WOT section of the PCV system. Since everything we know and have been taught is to maximize flow through that system. It just boggles the mind.
Maybe you've figured out why the restrictors? If not, the short answer is that it facilitates vacuum creation in the crank case. When at idle or low load, the PCV line on the plenum is trying to create a vacuum in the crank case. If there is no restrictor on the WOT section then the crankcase has full access to atmosphere (through the intake tract before the turbo or a filter venting to atmosphere on some modded setups). This makes it almost impossible to create a good vacuum inside the crank case. That's the main reason for the WOT line restrictor. I'm betting 95% of people who modify that section of the system have removed this restrictor. Now you have almost no vacuum at idle and low load situations.
The other restrictor? The one in the small PCV hose by the plenum after the PCV valve? I believe that is there to limit flow into the engine during idle so the engine doesn't get a large source of oxygen that by-passes the throttle plate and idle control valve. Without it, the engine could ingest a good bit of air at idle and there is no way a 850 rpm idle could be kept.
Oh, and where to connect the WOT PCV hose to the intake? Before or after the MAF? You want to do it after the MAF for a few reasons.
1) Absolutely no oil from blow-by should be allowed to contaminate the MAF element.
2) The air has already been metered so you don't want to double-meter it.
If you experience issues with the connection placed after the MAF, that is likely because you've removed one or more of your restrictors and your engine is now able to ingest a good bit of air quickly (the entire engine acts as a plenum in this case) before air even moves through the MAF causing it to register air flow.
Happy motoring!