from what i know, pcv's are use to vent the crankcase of blowby gases. engine draws air from the intake then pcv vent it to the intake manifold for burning with the a/f. that's the basic thing i know.

now, on a b16 there's a hose from the valve cover to the intake tract then a pcv is attached to the intake manifold. the pcv has a hose connected to it then routed to the plenum(i guess that's what it's called).

my question are: is the hose from the valve cover to the intake tract blowing air to the intake tract or is it sucking air in to the crankcase? where does the blowby gases pass to be burn with the incoming a/f, is it the through the hose connecting the pcv to the plenum?

i ask these question is bcoz i'm really confused as to what a catch can really does. i heard that you need a catch can to prevent oil from burning with the a/f so as not to reduce the octane rating of gasoline and also to prevent oil film inside the intercooler. so i tried to anylze how a catch can work and why is it needed in a boosted engine but not in an n/a but i still don't get it.

could anyone please explain how the catch can work and why is it beneficial. thanks in advance.

 

There has got to be a good post on this in the archives, did you do a search?

Basically, crankcase is under a slight positive pressure due to oil vapor and churning of the pistons. Fresh air comes IN the valve cover (due to slash cut in intake) and exits the back of the block through the accumulator and towards the manifold via the PCV valve. Under boost, no oil vapor should flow to the manifold becuase the PCV should close. At 1 atm the positive pressure will flow from PCV valve to manifold. At vacuum, the pressure differential between case and vacuum will cause vapor to flow or maybe not.

The catch can in series with the setup will remove much more of the oil vapor than the accumulator alone. If you use the catch can with no connection to the manifold, then PCV is achieved to the outside air. This is common in older domestic engines, but is illeagal by Federal law in every state and punishable by a $25,000 fine and prison time. Then again, most lawmakers don't know what a PCV is.

Why use it on a boosted engine? under high boost levels the positive pressure is really high and when you come out of boost the PCV valve can give your fuel charge a nice big gulp of oil vapor. This will increase the chance of detonation and may damage the engine. It is especially bad since many PCV systems vent right to one cylinder only, giving it all the punishment.

Good enough explaination?

Randy

 

Did my catch can install this weekend. Tried several different configs and this is my 2 cents.

The pcv valve is a one way valve that only allows vapors to travel from the valve cover to the manifold.

It only does this under vacuum.

I tried leaving the pcv valve in place and running a hose to the catch can then to a mini filter. Never opened. Had to take the pcv valve out to make it work.

 

so , coles notes=
get a catch can system

 

so now it's a bit clear. one more question, since the pcv regulates the vapor to the manifold, where does the vapor go? i mean, there's a hose from the top of the pcv connected to the plenum(where the t/b is connected to) and the pcv itself is connected to one intake runner. so which side does the vapor exit to be mix with the incoming a/f charge, to the plenum or directly through the pcv which attached to one intake runner?

 

Very good explanation, allow me to add a few points. The slash cut in the intake tube is the "ideal" way how fresh air is enter the crankcase. However, during boost situations, there isn't enough vacuum in the crankcase to operate the PCV valve. Therefore, any buildup pressure within the crankcase will escape to the least restricted path. In this case, the valve cover tube that connects to the intake with the aid of vacuum exists within the intake tube. The oil vapor then travels pass the TB and ended up in the intake manifold, rendering the slash cut useless. This is the very same reason why people experiencing oil coming out from their mini oil filter on the valve cover. I have used a catch can before in a closed loop system, but later switched to a open system instead without any catch cans.

Yes, it's illegal to not have a PCV system, but so is removing the cat converter.


[Modified by JT, 8:08 PM 8/26/2002]

 

thanks. things are beginning to clear up bit by bit. but there's one last thing.
where does those blowby vapors exit, is it on the end of the pcv itself where it is connected to one of the runners OR on the other end that is connected to the plenum(where the t/b is attached) via hose??


[Modified by _Endless_, 8:25 AM 8/27/2002]

 

The blow by gases will exit either through the breather valve or the pcv back into the intake manifold.

Under boost, the blow by gases will through the breather valve since the PCV will close when it sees boost. Its kinda like a 1 way check valve.

When in vacuum, the blow by gases get suck into the intake manifold by vacuum

 

-----
The blow by gases will exit either through the breather valve or the pcv back into the intake manifold.
Under boost, the blow by gases will through the breather valve since the PCV will close when it sees boost. Its kinda like a 1 way check valve.
When in vacuum, the blow by gases get suck into the intake manifold by vacuum
-----

Ok let me get this write… so after reading all that…. And above on a boosted car you should install a catch can to breath from two locations.

1 from the breather valve on the valvae cover, so the catch can.. can filter oil when in boost..

and no2 have it also filter after the PCV valve so separates any oil that the PCV has missed before it goes back into the manifold.

# 1 So from the valve cover – hose – catch can – hose – intake piping.

# 2 And also from the back of the block – hose - PCV valve – hose – catch can – hose – intake manifold.

And if I understand correctly.. on a non boosted car you would only need to catch can #2.. but on a boosted car you should catch both ?

Or have I completely lost the plot ??

Regards

James

 

Here's how I'm running:

Old: Valve cover to what was a cold air intake (prior to throttle body)
New: Valve cover to minifilter. No hole on intercooler piping.

Old: Valve cover PCV hose to manifold
New: Elbow (w/o PCV valve) and hose to catch can. Exit of catch can to 2nd mini filter. Manifold plugged.

 

You basically have an open system. Here is my open system. It's been this way for about a year.

 

I like yours better. I've got mine going to the filters up in front of the radiator above the IC.

 

seems like there's so many ways of setting this up.. its not funnie...

JT when you say u have a open system... is this what your system is.. ?

valve cover to filter under car

back of the block into pcv then to another filter under the car... or stright from the back of the block to the filer ?

of coruse havin the manifold pluged up... were the pcv hose used to run to.
Or are you using a catch can anywhere ?

Grrrr at 101 ways to set this up... there's so much wrong infomation floating around on this topic... its hard to work out whats correct.. and whats wrong.

Regards James

 

I agree that it's kind of confusing on how to setup a PCV system, because there are so many options. The method that I use is a complete open system without PCV valve or catch can. One hose (large) connects to the valve cover and the other end goes under the car with a filter (optional). The second hose (large) goes to the back of the block where the PCV valve used to be (PCV removed). The other end goes under the car with a filter (optional). This setup is very simple and works fine but not emission legal.