it's all EPA garbage. They want blowby burned again and processed by the cat converter. As the system comes from the factory it can't handle the volume of blow-by at WOT effectively enough to not hurt power output.

It's late, I'll go into to it more tomorrow (I teach high school auto shop BTW, so i'll break it down)

 

please do. i want a way to remove the charcoal box and still pass emissions. i did this in my evo

 

Thats evap not pcv bbs.

 

Subcribing for updates

 

All you need to do is run a catch can off the driver side valve cover and either vent it to atmosphere or plumb it back into the intake. If you plumb it back into the intake the catch can should have some filter material such as steel wool and baffle plates to remove any oil in the air.

Regarding valve cover seal (for Jon) there isn't enough pressure build-up for the vavle covers to seal unless you have a big problem with ring seal. New valve cover gaskets properly installed will not leak!

 

Subd

 

First off, I only really care about track performance and race cars and stuff. Factory stuff is always not best for these things.

The PCV system is designed to work best under conditions with high manifold vacuum, ie, idle and cruising, and low mass flows. It's that pressure differential that causes it to work. (insert some science about differential, flow potentials, orifice size, etc,) Pressure differential is my primary theory i work with, for everything.

Identify your orifices, where differentials exist, mass flow, and when and how these variables change (or don't change).

Under cruise and light throttle there is less blow by for various reasons..... rpm (which affects ring seal), cylinder pressures, etc, so there is less mass flow to deal with, AND there is a greater pressure differential across the orifice leading to the intake via the PCV valve, orifice sizes stay the same.

Once you go WOT, blow by goes up, orifice sizes stay the same, and differential changes because now there is virtually no vacuum in the manifold, so now you have more mass flow to deal with, no assistance from the differential created by the intake manifold, and the orifice sizes are TOO DAMN SMALL to be ideal at WOT. Even if leakage percentage per combustion event staid the same, as RPM goes up the numbers of events where leakage occurs also goes up.

At 6000 rpms each cylinder is firing 50 times per second......... at 3000 rpms 25 times per second, and as VE and cylinder pressures go up leakage probably will too.

 

Right in Nissan's own service manual, it's not sufficient at WOT or with high blow by.

If someone has some valve covers they can take pictures of where PCV hoses and items attach it'll be clear as day.

 

you have to disconnect any PCV attachment from the intake manifold if you go this route.

We drill out the PCV valve hole and tap it for a largest NPT nipple we can fit, same for the inlet that usually attaches to the intake pipe, except we just drill out the restrictor. On the FWD VQ (and probably RWD) there is a hose that runs from one valve cover to the other, this would be another good point to open up the holes or add NPT nipples and a T fitting. At that point you'd have 3 points for the crankcase to vent. You'll lose a bit of oil, so routing everything to a vented catch can with a separator and a drain that drains back to the sump (above the oil level) would be ideal because any vented oil would be reclaimed.

 

I dont know if this helps but it will be here for reference. These are valve covers off a de.

 

there is 2 questions that I keep asking myself about this,

I have a little problem to understand everything correctly.
In my mind if you vent to atmosphere the PVC
and the valve cover still connected to the Intake pipe.

Aren't we losing air that is metered by the MAF sensor thus losing air going in the engine.
or it would pull the air from the crankcase to be aspired into the inlet from the intake pipe.


From my fluid dynamic understanding is the air will take the path of the least resistance which is the inlet from the intake piping.
so we are getting unmetered air into the intake manifold since its sucking air from the valve cover because of the small vacuum that is in the intake piping
Am I right ?


right now I'm just guessing on what you said previously on getting 5-10hp by doing this.
would it be because your MAF tube is a chocking point and you are getting IN more air by sucking from the valve cover which is also vented to atmosphere

 

here's a picture I took of a 2.5 valve cover a while back...... it's of the nipple on the valve cover that attaches to the intake inlet pipe. Unless you take a really close look all you see is a fairly large hose and nipple and assume it flows as much........

once you take a close look, you'll see that there is a built in restrictor, there has to be or throttle body wouldn't be able to control the idle speed of the motor.

(sorry for the profanity, only pic i have)

 

yea realized that lol, my bad. i did the pcv mod before, wanna get rid of the evap without a code

 

The ECU can compensate up to around +/-25% in fuel corrections before it freaks out. What I'm suggesting is to disconnect the PCV hoses from both the intake manifold and intake inlet piping, then there is no air meterd or unmetered lost or gained. Then make every possible point where crankcase pressure can exit the motor, as large as possible so pressure in the crankcase at WOT and high RPMs can be lower. You will lose oil if you simply vent the crankcase, so if you vent to a vented catch can with a separator and drain the oil will make its way back to the crankcase.

 

thank you for the pictures

I bet one or more of the nipples has a restrictor in it, it's hard to notice.

 

Thanks for the info

 

I will look at them when I get home.

 

This is the only restrictor I found. Its located on the left bank valve cover (D/S), its the rear outlet.

 

At WOT, there is basically no vacuum in the system because the motor is not creating any vacuum. Obviously if there is no vacuum, the PCV system cant pull out vapors. Hence the statement in the FSM and every FSM about PVC systems. Your statement about the system not being able to handle the blowby is taken out of context. As no system without an active vacuum pump could do that.

YOu need a mechanical pump if you want to create vacuum at WOT. Drilling holes, adding catch cans has nothing to do with maintain a vacuum to continuously pull vapors effectively at WOT.

What crankcase pressure are you talking about with a NA car? Its always equal or less than atmosphere. So you cant create positive pressure in the crankcase without pushing air into the motor greater than 1 atmosphere. You can add catch cans, drill holes etc to catch oil vapor, but you are doing nothing to prevent that issue at WOT without a mech pump.

If you are talking about a boosted car, there are hundreds of post already about this subject, in which case you eliminate a manifold vacuum source completely and focus on reducing the crankcase pressure that can be caused by boosting.

some more reading
http://forums.nicoclub.com/positive-...d-t446254.html

 

I never said create vacuum, simply reduce crankcase pressure. Like I said, it's all about pressure differentials, orifice size, and mass flow. You need to read the article you suggested I read.

the system is designed to comply with federal regulations and regular driving, not racing conditions, extended WOT running, extended redlines, increased cylinder pressure, and the amount of increased blowby and crankcase pressure that those conditions create. the motor and related auxillary and emissions systems weren't designed for those blowby mass flow rates....... more mass flow in a given time period with an unchanged orifice size = higher pressure, you loose some of the motive force of differential at WOT due to no vac in the intake manifold, so now the increased flow is forced to reverse, because the pcv valve is maxed out, and go out the "in" tube, even from the factory, read the whole passage from the FSM page I posted. Once you are at that point (meaning racing the car like we do on a regular basis) the only variable you can really change without adding a vac pump is to change orifice size, aka, that tiny hole inside the misleadingly large PCV tubes on the valve covers.

Adding a vac pump increases differential, which is the motive force for mass flow of a gas, but you still have to address orifice size for the pump to work correctly. If you hooked a pump to the valve cover vent tube and then couldn't figure out why the pump wasn't pulling vacuum like it was supposed to, it would be because you didn't take the time to read what I've been writing. If you are already venting to atmosphere, you can relieve more pressure (and all the nasty gasoline and gunky **** vapors in blowby), which is what you want to do anyway if you are modifying the PCV system to vent, if you address the orifice size it's win win, very cheap, and makes more power, you just have to realize you'll be losing more oil quicker, so if you catch it, separate it, AND send it back to the sump, it works great (for a race car or highly modified car).