Crankcase Evacuation Discussion

[DoubleD]

I am looking to get a discussion going on crankcase evacuation. I know how important it is to get the pressure out of the engine and it is even better to keep it under a slight vacuum if possible. I have an IROC R/T and I have done a lot of research on this topic and I think I have come up with a good way to properly vent the engine and not put oil back into my intake. Here is my current set-up. Let me know what you think.

[1BADVAN]

Looks awesome! are those white connectors plastic from Home Depot or similar? I have always just let mine vent to atmosphere, I prob should hook it up to something

[DoubleD]

They are just 5/8" Tee and angle barbed connectors from the hardware store (Menards) From my research venting to atmosphere is not the best way having it plumbed into the intake side pre-turbo is a better solution.

[RIMoparGuy]

Is there any negative effect to venting it into the atmosphere? Mine is currently hard-lined into the exhaust pre-cat and will probably just cut it to vent.

[rbryant]

Make sure you have a venturi on the barb for the turbo inlet or you won't get any suction under boost.

Also with that configuration you will probably suck most of the air through the baffled catch can from the turbo inlet not from the valve cover when in vacuum...
The best system will act like a normal PCV system when not under boost and will switch to draw from the intake through the oil seperator under boost.

Another check valve and/or solenoid or two catch cans that are completely independent is the best way to do that. (perhaps someday I will actually try it).

-Rich

[Shadow]

Is there any negative effect to venting it into the atmosphere? Mine is currently hard-lined into the exhaust pre-cat and will probably just cut it to vent.

No, there is No negative effect and this is how all the high HP turbo cars are doing it. Large enough volume flow to a filtered to atmosphere catch can and your set

[DoubleD]

I was finding more oil in my intake and turbo than I would like. The set-up I am currently using is not working, in fact I believe my pre turbo vacuum draw is rendering my pcv system inoperable. It is going to need an overhaul. Rich, I agree with the need to replicate the stock PCV system, I am just not sure where to vent the air while under boost.

Here is one idea I have had but I am still not happy with it.

[johnl]

Make sure you have a venturi on the barb for the turbo inlet or you won't get any suction under boost.

Also with that configuration you will probably suck most of the air through the baffled catch can from the turbo inlet not from the valve cover when in vacuum...
The best system will act like a normal PCV system when not under boost and will switch to draw from the intake through the oil seperator under boost.

Another check valve and/or solenoid or two catch cans that are completely independent is the best way to do that. (perhaps someday I will actually try it).

-Rich

Rich, my fault I'm sure but when you say "suck most of the air through the baffled catch can from the turbo inlet not from the valve cover when in vacuum" I'm not follwing you. Where else would the air come from if not from the valve cover? I can see where it could be sucked backward into the intake manifold . . . my blindspot.

[Ondonti]

I changed my exhaust evac setup to include the original OEM 3.0 pcv valve and it seems to work great. DOUBLE check valves in series on the downpipe so at high vacuum, low exhaust flow the pcv is doing the work. I do need to get a small check valve for the PCV to deal with boost better.

People running dry sump should never run an open vent setup so I would still say drawing the gases out is always the best policy. Sometimes its hard to get good results without a baller dry sump. The best that open atmosphere can get is near zero crankcase pressure. Exhaust evac will do better then that but it does not work at low loads/idle. Not at all. You will leak oil without a secondary system that WORKS at high vacuum situations. People don't seem to do well at that for some reason so the no brainer is aggressive open vent setup. Custom intake manifolds usually don't have pcv setups and I don't know that I have faith in slash cut intake manifold setups for high vacuum situations. I don't have any idea how I will use "pcv" + exhaust style setup in my P body since the intake manifold has no pcv Better off open vent then massive leaking at idle.

[Vigo]

I REALLY dont understand the reasoning behind the setup DoubleD is running.

Looks like the way it is setup, the PCV will be made less effective or totally useless by the fact that it can suck air in through the catch can instead of being forced to pull from the crankcase.

I think the best setup that retains PCV function is basically the stock system's routing, with a catch can added between the 3-way elbow and the turbo, a special tube thing i forget the name of in the intake tube to promote vacuum, and upgraded for higher flow out of the crankcase.

[rbryant]

Rich, my fault I'm sure but when you say "suck most of the air through the baffled catch can from the turbo inlet not from the valve cover when in vacuum" I'm not follwing you. Where else would the air come from if not from the valve cover? I can see where it could be sucked backward into the intake manifold . . . my blindspot.

The drawing in post #1 didn't have a one way valve from the Tee (between the breather and PCV valve) so when in vacuum it could suck air directly from the turbo inlet.

-Rich

[DoubleD]

Here is my theory behind what I came up with...
I can explain in more detail but here are some drawings for air/oil flow.
Under Vacuum

Under Boost

[rbryant]

I was finding more oil in my intake and turbo than I would like. The set-up I am currently using is not working, in fact I believe my pre turbo vacuum draw is rendering my pcv system inoperable. It is going to need an overhaul. Rich, I agree with the need to replicate the stock PCV system, I am just not sure where to vent the air while under boost.

Here is one idea I have had but I am still not happy with it.

In this setup you don't have a vacuum source when under boost.

Think about creating the stock factory PCV system for a 2.2/2.5 or Neon NA car when in vacuum.

Then add check valves to isolate that system when in boost. After that you want to run the "slash cut venturi" line from the turbo inlet when in boost which goes through an oil separator to the valve cover the oil separator is so you don't fill up your intercooler lines with the oil. The other side of the valve cover is sealed and the vacuum draws directly from the sealed valve cover to the turbo inlet when under boost. It is the same setup as an exhaust suction line except it uses the oil separator and the intake instead of directly putting oil into the exhaust which is generally not emissions legal.

The venturi is required to increase the vacuum provided from the turbo inlet to something sufficient to vent the crankcase. The other main difference in this setup is that it requires the normal PCV line to be sealed which is different than the NA setup. Some PCV valves may work well as check valves and others need a check valve to really seal that side of the system when under boost.

My real proposal on this stuff is that there should be solenoids that sway from one system to the other rather than check valves.

The stock system actually does some of this depending on how well the PCV valve acts as a check valve, how well the rubber Tee acts as a venturi, and how much suction is actually available in the airbox when under boost.

Alternatively buy an vacuum pump and just always connect to that instead of the intake on an NA style system. The problem is that the pumps are expensive and actually banned in some racing because of the slight horsepower advantage they give.

-Rich

[rbryant]

Here is my theory behind what I came up with...
I can explain in more detail but here are some drawings for air/oil flow.
Under Vacuum

Under Boost

Yea that should give you an open vent when under boost and stock NA style PCV when in vacuum.

For the non boost system:

As Vigo noted: I am not sure about the check valves and connection from the PCV valve side of the breather to the catch can. The path to the catch can should go through the valve cover not around it.

Here is an 88 NA vac diagram from http://thedodgegarage.com



The PCV connects directly to the valve cover on one side and the Air cleaner connects on the other.


For your boost system...

There is an advantage to getting some suction when under boost with the slash cut system rather than the open system. Plus the open system is not emissions legal in most places.

-Rich

[DoubleD]

What would this slash cut system look like? I could take the line that has the filter on it right now and re plumb that into before the turbo, I just thought my problem before was that I had too much vacuum on that side. When the car is running at vacuum at high way speed, will intake side of the turbo be in vacuum or will that be near atmosphere. I am trying to still wrap my head around a proper PCV system, I think I am getting close thou...

With my original design on the top of the page my car was acting weird. I actually took and removed the PCV valve, i capped the hose going to the intake manifold and I capped the adjacent part of the "Tee" The car ran much better then under boost. I'm still not sure what that was.
Here was that try..

[rbryant]

What would this slash cut system look like? I could take the line that has the filter on it right now and re plumb that into before the turbo, I just thought my problem before was that I had too much vacuum on that side. When the car is running at vacuum at high way speed, will intake side of the turbo be in vacuum or will that be near atmosphere. I am trying to still wrap my head around a proper PCV system, I think I am getting close thou...

Post #13 describes the slash cut system or you can google it.

The vacuum when not under boost should be much lower than when in boost as it is purely based on the amount of air the engine is sucking in. It will suck in more air through the turbo when under boost as it is making more horsepower.

Although hard deceleration is also a concern and might have to be dealt with... I will have to give some thought or research to how much air flow goes through the turbo on deceleration (I know internal engine vacuum is high but what about the actual flow into the engine through the air filter).

If you really get too much vacuum through the slash cut then a PCV valve is a device designed to fix that exactly the same way that it works on the intake manifold. It is all about sizing it right. I would put a vacuum gauge on the slashcut line and see what you really get. If it is too much vaccum then put in a PCV valve that flows the amount you like in that line to regulate it.

That is why I like the idea of having motorcycle solenoids that switch from one system to the other when you hit something near 0 boost/vac.

-Rich

[DoubleD]

My set up from the top also yielded more oil than I want in my intake, the tubing leading up to my turbo was covered in a thin layer of oil..

[DoubleD]

Still working thru some ideas...
Here is the stock TIII PCV set up, I have been told by numerous people the stock set-up is not enough for a modified car, you need to vent both valve covers too.


Here is another idea I was working thru, Under vacuum it operates as factory. The air goes straight from the crankcase into the intake, but under boost the air goes from the crank case and valve covers thru the catch can and onto the vacuum side pre-turbo. This set-up will draw the air out of the CC and VC's. I still have not figured an easy way to pull the air out of the valve covers under vacuum.

[DoubleD]

Here is my 2014 Plan, I am going full vented, I found a lot of oil in my intake pre-turbo. I will try fully vented this year with two different systems and two filters. If this plan works I will look to integrate them again next year after I freshen up the motor.

[Shadow]

Awesome! You should find this set-up Way simpler and should work Great! (dang, just look at all the hoses and crap you got rid of!)