Catch Can Oil

[AMpcass]

:bash
Why bother?--------IT can be proven in every single Corvette engine, from pre c4 to present, that if you rev it, positive pressure in the crankcase is produced.
This pushes crankcase vapor out the fresh air tube, into the manifold, where it condenses.
So now if the vapor that would normally be sucked into the engine and BURNED with the PCV system, reverses based on RPM and gets sucked in the engine through the OTHER SIDE of the PCV system, what is abnormal????
Allthebest, c4c5

Correction to the myth of positive crankcase pressure: it does not exist. There is always a vacuum present of -1 to -9 mm. I have a meter on this in fact. Also, I have two catch cans installed, which for ME is a lifesaver.

so which is it?

 

[c4c5specialist]

HI there,
I stand by my statements.
Also, if there is no positive pressure, how does the OIL VAPOR get UP to the fresh air intake hole, just behind the bolting point of the throttle body?
Allthebest, c4c5

 

[NORTY]

HI there,
I stand by my statements.
Also, if there is no positive pressure, how does the OIL VAPOR get UP to the fresh air intake hole, just behind the bolting point of the throttle body?
Allthebest, c4c5

If there is "no positive pressure" downstream pushing the oil, then there must be a vacuum "upstream" to pull the oil. I don't believe the surfaces are close enough to create "capillary action" however.

Just thinking of something else...how about the velocity of the gases going through the PCV system lines?

 

[TODD L GRIFFITH]

Here is the way I look at it. 14.7 psi. is considered atmosheric pressure, or 1 atmoshere at sea level. This is the MAP sensor reading with the engine off.
Anything less than 14.7 psi at sea level is considered negetive pressure or vacuum pressure. An engine at idle should have a MAP pressure reading of +/- .800 psi. This is negetive in relation to atmosheric pressure, or considered vacuum pressure, or negetive pressure subtracted from 14.7 psi.
However, the more the throttle is opened, the more positive the MAP pressure becomes, allowing more air into the intake, but is still less than one atmoshere or 14.7 psi.. Out on the open road at WOT above 50mph you may see a MAP pressure close to 1 atmoshere. (14.7 psi.) The filter efficiency, or pressure drop of the filter comes into play and may result in a MAP reading of 14.5 psi. or a .200 psi pressure drop at the filter at this time.
Any reading above 14.7 psi is considered positive boost. This can result from a RAM air setup, or means other than naturally aspirated as we all know. A MAP of 15.7 psi is considered 1 psi of boost.
Now you all can tell me I'm wrong, the flame suit is on.

 

[c4c5specialist]

If there is "no positive pressure" downstream pushing the oil, then there must be a vacuum "upstream" to pull the oil. I don't believe the surfaces are close enough to create "capillary action" however.

Just thinking of something else...how about the velocity of the gases going through the PCV system lines?

Then, the velocity would take the vapor DOWN through the crankcase away from the fresh air intake at the throttle body and UP to the PCV valve.
If you notice in any oil residue issue, it is always on the FRESH AIR side inside the hose.
Allthebest, c45

 

[c4c5specialist]

Here is another way to look at it.
Now, the vacuum placed on the PCV system from the vacuum of the engine comes through a certain size hole, be it from the PCV valve of a fixed orifice to METER the air being ingested from the crankcase system into the engine during operating conditions.
We all agree that the pistons COMPRESS air and fuel into the cylinders, creating power.
Now, why is it that the same condition cannot be said for the crankcase?
Your orifice is still fixed, it has not changed.
However, at higher rpms, the pistons running up and down at a higher rate of speed create more pressure that CANNOT be overcome by the same orifice that is allowing that same predetermined amount of air into the engine to burn.
It has to go somewhere, so, it will go to the point of least resistance, the FRESH AIR INTAKE. The vapor then condenses on the cold throttle body/intake area and your condition.
GM realized that the only way to substantially reduce the conditions on the higher revving engines, was to make it integral into the lower valley cover, like on Gen 4 small blocks in c6. That way, it doesnt condense on colder parts and produce oil film.
Allthebest, c4c5

 

[TODD L GRIFFITH]

Like I said before, I've seen oil at idle being pulled up from the oil valley tube into the can. (clear tubes, transparent). If the catch can wasn't there, it would be pulled into the intake through the PCV under vacuum. Not only oil is pulled, moisture as well at start-up.

 

[c4c5specialist]

Which is normal.
Allthebest, c4c5

 

[NORTY]

Then, the velocity would take the vapor DOWN through the crankcase away from the fresh air intake at the throttle body and UP to the PCV valve.
If you notice in any oil residue issue, it is always on the FRESH AIR side inside the hose.
Allthebest, c45

Thanks for the clarification. I was thinking about all the reciprocating surfaces (piston bottoms) and the turbulence they create.

 

[AMpcass]

Now that we know that oil vapor gets into the air intake and that the use of a catch can collects that oil instead of allowing it to go thru the intake valves, does the catch can enhance the engine life/performance or degrade it by preventing a form of top cylinder lubrication?

 

[c4c5specialist]

HI there,
There is no actual data to indicate the catch cans either HELP OR HURT engine life or performance.
No company has any documented testing of validation of catch cans.
Allthebest, c4c5