NewbVetteGuy

Can some of you give me a quick primer on oil control and crank case vacuum/pressure or even exactly what constitutes the "crank case", exactly?

I can understand everything in the bottom half of the engine being called the "Crank case" but I don't understand how the crank case connects to the rocker cover area.


Windage Trays, Crank Scrapers and how pressure gets generated, why it's bad, etc...



I'm really interested in what goes up in the rocker / valve covers and how the breather systems are supposed to work, when to use an oil catch can, why some valve covers have hoses connecting the left and right banks, etc...


I think I at a basic level get windage, understand a few mechanisms to control it, that vacuum can help oil particulates fall out faster, that "ring flutter" can occur at high RPM and reduce power because of pressure that's blowing by the rings and getting into the crank case, but the practicality of it all, I'm missing: How much power are we talking about for each of these, what constitutes "high RPM", and especially vacuum vs. pressure and how all those breathers and hoses on top of the valve covers help.




Adam
P.S. I'm happy to read links to other sources; no issues there.

MelWff

the crank case is an old term for the oil pan
have you ever seen the inside of an engine including the cylinder heads, that would help you understand how vapors get from the bottom to the top of the engine.
by using google you can find lots of information on the topic you are inquiring about, below is an example.
http://www.enginelabs.com/engine-tec...d-air-control/

Alan 71

Hi Adam,
Here's a simplified drawing that illustrates how 'blow-by gases' are evacuated from the crankcase through the pcv system.
Notice the crankcase breather in one valve cover and the pcv valve in the other.
Perhaps you'll find it informative.
Regards,
Alan

cv67

every time a piston comes down, the air behind it has to have somewhere to go.
There are holes in your lifter valley, timing cover area and cyl heads where it can travel but still needs an escape path thats what your breather/pvc helps out with. Add in blowby from old rings it gets worse, adding stroke same thing. Real long strokes ran really try to whip your oil up into a froth, hard cornering etc. Good oil pans windage trays help out also gotta upgrade everything .

NewbVetteGuy

Thanks that helps. The PCV generally doesn't make any sense to me; why is it good to fling oil into the intake and the intake valves and back into the inside of the cylinder where it can lead to detonation??!?

Is it simply because with open breathers the oil gets splashed around the outside of the engine? My thinking right now is just to use dual breathers and no PCV.

I'm also confused a bit by how the diagram works when you've got dual breathers installed because I thought the breathers had baffles inside that only allow air out and don't allow air back in...??


I'm also confused by the diagram showing the air coming in one side and always going out the other side- wouldn't it be the opposite for the other side of the engine? Is the air really unidirectional? (because the crank is always spinning in the same direction?)



Adam

NewbVetteGuy

HA! I'm reading the Engine Labs article right now and I'm proud of myself for asking about the oil being re-introduced ala the PCV to the intake, here's a direct quote from Moroso on a problem with stock PCV's (I'm slowly learning, but I'm learning!):

“Removing this oil mist before it reenters the engine reduces detonation, and deposits on the intake track, including the valves themselves,” according to Moroso’s Thor Schroeder.

Buccaneer

Check this site out, has some good info on the entire system and how it works. I have their PCV in my new motor, works awesome, easy to adjust and no more oil leaks.

http://mewagner.com/

jim2527

For the most part its not a big deal. LS engines can have so much blow by that 'catch cans' have become very popular. Heck, GM even lists a 'catch can' for use when tracking.

NewbVetteGuy

What I really don't understand is why the catch can is even necessary or good; why can't someone design a breather that just separates the oil and air and drops the oil back into the valve cover so it can drain like it's supposed to?

Injecting it into the intake seems stupid, pulling it out of the engine entirely ala a catch can seems stupid. The oil is important but it shouldn't be injected into the incoming air stream, right?


Adam

maj75

BMW did. It's made of plastic and meant to drain into the pan. Until they get old and crack and leak oil all over. After the warranty expires.

NewbVetteGuy

Well, I felt like I was starting to understand this until I read the site that Buccaneer linked to...

http://mewagner.com/?p=1130

This article seems to indicate that for some reason with breathers the engine is under constant pressure....??!?? I don't understand. If the breathers appropriately open to let any pressurized air out, wouldn't that solve the problem?


Why are the results with PRV valves almost always better regarding pressure / vacuum levels in the crank case?


Adam

NewbVetteGuy

You require 2 of these, right? ($250 for PRV valves???)


Adam

ddawson

No just one because one side is sucking and the other is blowing "vacuum".

I can hold my hand over the breather tube and it's like a vacuum hose.

As for scrapers and windage, think of the difference running in a pool of water vs on dry land. The fluid slows you down.

SH-60B

PCV is Positive Crankcase Ventilation. Breathers alone would merely be passive. The PVC system is for vacuuming out crankcase blowby gasses that contain moisture and of course other corrosive compounds that would quickly contaminate the oil, and sludge up the crankcase. The oil mist you're talking about is beyond the factory PCV system's ability to separate, and that's where a catchcan is useful. Why is collecting it in a catchcan stupid? If it's collected it won't be re-introduced into the intake.

Silvertone

I just got this ME Wagner dual stage PCV to attempt to improve scavenging at cruise while restricting flow at idle. I used stainless steel wool scrubbers to help catch oil mist both in the catch can and in the valve cover insert. The left side valve cover has the open breather.

I believe the idea is to create a slight vacuum in the crankcase to help seat the rings and prevent pressure from blowing oil out the seals.

Steve

jim2527

Modern engine oil lose through a catch can is minimal...depending on who you talk to. Guys over in C6/C7 tech go into full blown V-tach panic attacks over this. There's a single drop of oil in my intake the world is ending GM needs to pay to have my intake and valves cleaned I'm having a panic attack Some of them want the inside of their engine to be as clean as their floor mats.

But seriously, its all part of modern emissions, venting it to atmosphere isn't 'good' so its re-routed back into the engine and burned off.

Buccaneer

No, you only need one and almost any price within reason is ok if the motor runs better and no oil leaks. The theory is pretty much straight forward and what Alan posted is the system in a nutshell. The site goes a long way to help understand more how PCV works and why you need to adjust the PCV for a certain amount of vacuum, especially if your motor is more high performance than stock.

Silverstone, how do you like yours and the setup you are running? Thanks

Alan 71

Hi Adam,

"The PCV generally doesn't make any sense to me; why is it good to fling oil into the intake and the intake valves and back into the inside of the cylinder where it can lead to detonation??!?"

On a clean engine ONLY blow-by GASES are being brought back into the induction system to be burned with the regular intake charge of gas and air.

Regards,
Alan

gkull

Let's me list some true facts!

Our 4 cycle motors from valve cover to the oil pan is a air chamber

Motors make the most hp with @20 inches of vacuum.

The best system to create a 20 inch vacuum is a dry sump oil scavenging system with an adjustable fresh air bleed to the cam valley area to not exceed the 20 inch value

The next best system is electric or belt driven evacuation pumps

Big free flowing breathers are next even though they just maintain no pressure

In last place is for people who don't desire performance. The pcv system. Intake manifold vacuum is the highest at the lowest throttle opening. Which is also the point of lowest hp and cylinder pressure. Which is also the least amount of ring blow by. Your pcv will be flowing through the most air and oil mist. At wide open throttle you have the vacuum drop off to the lowest point, the highest hp, and the most blow by. The pcv is flowing through the least and not helping and actually containing crank case pressure very dumb idea. Pcv is also a variable vacuum leak to the air fuel system. Another dumb idea

maj75

You forgot plumbing the breathers into a hose to the header collector. That generates the highest vacuum at the highest exhaust velocity. Also the simplest, since a passive breather doesn't create any vacuum.

I run a catch can on my C5 track car. After a shortblock replacement, I did my first track day. While replacing the shortblock, I also switched to the LS6 valley pan which rerouted the PVC hose connection. I opened the catch can after the first 30 minute session and it was almost full. I was losing almost 1/2 quart after each session into the catch can. The back of the car was covered in oily mist. We discovered that the valley pan baffle was defective and was allowing un-baffled air into the PVC hose. We switched the valley cover and no problems since. For comparison, my son's C5 Z06 generated about 2 tablespoons of oil for each track session.