yamahaSHO

Pressure on intake piping is lower than the pressure in the crankcase.

06Estukay

Delete it. My intake ports have never looked so clean since I did it. As long as you have enough venting, the pressure will find its way out. For what it's worth, my dip stick stopped popping out since deleting the pcv. Under full throttle, the pcv is closed. By removing it, you're actually allowing more crankcase pressure to be vented. I used a simple M18x1.5 to barb fitting where the stock PCV was, routed to a baffled catch can vented to atmosphere.

Apex1.0

Excess crankcase pressure needs to be evacuated fast enough. So normally the vacuum in the manifold draws crankcase gas through the PCV. Fresh air is restored to the crank from the port going to the air inlet tube. During closed/low throttle position (high manifold vacuum) the pressure in the intake tube is high relative to the manifold.

When you go to WOT the system can work the other way. There is zero pressure in the manifold which closes the PCV valve. However you have an excess of blow by from WOT combustion that is pressurizing the crank case. That pressure can be expelled out the fresh air tube in the intake pipe. During WOT there is a slight pressure drop in this tube that will aid in expelling the gases.

FWIW, I would go with a closed system (with catch can) or a dedicated vacuum pump system long before I would just open the system to the atmosphere.

06Estukay

Theories are great, but experience is better. I've tried all the B.S. with trying to maintain the PCV valve (track car). It doesn't work. I removed the PCV valve and vented straight to atmosphere. I actually tear down my motors and inspect everything. It works.

Let's keep in mind why modern PCV valves exist - it is solely for emissions purposes, and cannot be compared to a vacuum pump. The whole idea is to send crank case vapors through the combustion chambers to burn off excess gas and send it out through the cat and tailpipe. These vapors have contaminants, like vaporized oil. Oil in a combustion chamber reduces efficiency, increases probability of knock, cakes on piston tops, valves, etc. Don't believe the hype on the intrawebs that engines require a PCV for it to run optimally.

Drag racers use vacuum pumps for a totally different reason than you're alluding to. The vacuum pumps are used to create vacuum even during WOT pulls down the strip. Vacuum in the crank case reduces windage, which increases power, and to aid ring sealing. The vacuum created in the crankcase for a system with a PCV valve is only effective during light to no throttle conditions. Totally different.

No, it does not work the other way. When the PCV is closed, the loop is essentially closed. The amount of pressure drop in the tube is infinitesimal and will not provide any significant pulling of gases from the crank case.

Under full engine load, I'll take 2 vents (front breather + PCV removal) vs 1 vent (front breather open only with PCV closed).
So yah, FWIW, what you would go with is irrelevant since this is your opinion and not quantified by any actual testing.

King Tut

I like this guy.

Apex1.0

A little touchy are we? If I had a fresh engine build blowing out dipsticks, I guess I would be too.

The side with the PCV side does close. The inlet side of the system can and will flow the opposite way at WOT. I don't know what kind of experience you have, but that is how the system works. I agree cars that use vacuum pumps are to have the benefit of vac at WOT, however there are benefits to having vacuum on the crankcase at all throttle positions. It will help the rings seal, this is a benefit to efficiency even at low to mid throttle positions.

So yeah if you like having the crankcase force the extra blow by out two holes under pressure, good for you. I hope you got a good ring seal when you broke in that motor.

yamahaSHO

Just about every tracked S2000 I've seen with the factory PCV setup pushes up the dipstick of the seal is needing replaced. Mine used to do it and then I got a new dipstick with installed seal and it didn't do it anymore.

06Estukay

A little touchy are we? If I had a fresh engine build blowing out dipsticks, I guess I would be too.

The side with the PCV side does close. The inlet side of the system can and will flow the opposite way at WOT. I don't know what kind of experience you have, but that is how the system works. I agree cars that use vacuum pumps are to have the benefit of vac at WOT, however there are benefits to having vacuum on the crankcase at all throttle positions. It will help the rings seal, this is a benefit to efficiency even at low to mid throttle positions.

So yeah if you like having the crankcase force the extra blow by out two holes under pressure, good for you. I hope you got a good ring seal when you broke in that motor.

[/quote]

Not touchy at all. Just trying to help others from being misled from false info being spread around by someone with no real world experience on the matter. Where did I say that I had a fresh engine blowing out dipsticks? Stay on point and don't be a dick.

OEM motors blow out dipsticks all the time on track. Search the forums, talk to local members who track their S2000's often. It's a sign of excess crankcase pressure with nowhere to escape. The pressure will find its way out, and its very common for the pressure to blow out the dipstick hole. That's a clear sign that the OEM PCV system is inadequate at venting excess crank case pressure.

Much of what you're saying is wrong and based on assumptions.

1) High manifold vacuum created under closed throttle is one of the factors that helps seat rings during break-in. The opposite and equally important factor is adequate cylinder pressures, i.e. high load. And once the rings are seated, they are seated. By your logic, any race motor without this emissions control system, the rings will never seat, and will never seal during normal operation. We know this to not be true.
2) The PCV valve is closed under WOT. This effectively seals up one of the two ports used to vent crank case pressure. That vacuum that you talk about is non existent under WOT. The closed PCV causes more pressure to build inside the crank case. This pressure is working against your rings from seating. But they still seat, because the cylinder pressures far exceed the pressures in the crankcase.
3) Under WOT, you've only got the front breather to help bleed off excess crank case pressure back into the intake. 2 ports for crank case pressure to bleed is better.
4) PCV's are emissions devices so we don't have cars with smelly engine bays and dripping oil vapors on the road.
5) PCV's are easier for end users to maintain their cars. Imagine if OEM's installed catch cans from factory that required emptying all the time?
6) Recycling nasty crank case vapors into your combustion chambers is not ideal.
7) The effect of the manifold vacuum on the crank case is negligible. The 3/8" PCV line running from your intake manifold to your valve cover is like you sucking on a straw sealed around massive garbage bag. How much volume do you need to suck through that straw to create any significant vacuum?

But don't take my word for it...
http://www.hotrod.com/how-to/additio...s-and-answers/
http://oppositelock.kinja.com/ditch-...ate-1634156554
http://www.superstreetonline.com/how...lation-system/

You're making assumptions and speculating without actual experience. Let me know your findings when you try both ways.

yamahaSHO

My diesel truck came with one in OEM form. It sucks and causes the radiator to be clogged over time from vapors that escape.

cleenyc99

from my under standing working as a mechanic my hole life + years of factory and outside schooling. the PCV valve is open and flows the most vapor at WOT. high Crank case pressure + low vacuum = open valve. the PCV valves job is to assist the CCV at high rpms when CCP is at its highest. the only reason there is a valve and not a straight hose is so in the event of a backfire it closes protecting the engine.

Recycling crank case vapors into your combustion chambers is 100% not ideal and the engine vacuum does little to help the flow of CCV or seal rings