PCV System Details
Thread Starter
Burning Brakes
Joined: Mar 2009
Posts: 830
Likes: 6
PCV System Details
Team,
the car in question has a stock L98 motor, 1990 6sp which is autocrossed regularly.
Engine has been resealed. Performance / power is excellent. However since all the leaks have been sealed I have noticed I pump oil out the dipstick.
I have searched the numerous threads here and other sites, and feel I am not getting enough pull off the PCV under WOT. I have brand new AC Delco PCV valves and fresh hose, nothing blocked. Was thinking of cutting in a breather but I a couple of the threads implied that one side the PCV sucks and the other it doesn't, not sure why I it would work that way. Seems to me that both the line running to the throttle body area and the other to the manifold.
What I was considering doing is putting a breather element in line between the PCV valve and the intake, with a T that can be capped for street driving but opened for track and autocross events.
Thoughts, examples of other solutins?
Thanks
the car in question has a stock L98 motor, 1990 6sp which is autocrossed regularly.
Engine has been resealed. Performance / power is excellent. However since all the leaks have been sealed I have noticed I pump oil out the dipstick.
I have searched the numerous threads here and other sites, and feel I am not getting enough pull off the PCV under WOT. I have brand new AC Delco PCV valves and fresh hose, nothing blocked. Was thinking of cutting in a breather but I a couple of the threads implied that one side the PCV sucks and the other it doesn't, not sure why I it would work that way. Seems to me that both the line running to the throttle body area and the other to the manifold.
What I was considering doing is putting a breather element in line between the PCV valve and the intake, with a T that can be capped for street driving but opened for track and autocross events.
Thoughts, examples of other solutins?
Thanks
Burning Brakes
Joined: Jun 2008
Posts: 892
Likes: 1
From: New Smyrna Beach Florida
Team,
the car in question has a stock L98 motor, 1990 6sp which is autocrossed regularly.
Engine has been resealed. Performance / power is excellent. However since all the leaks have been sealed I have noticed I pump oil out the dipstick.
I have searched the numerous threads here and other sites, and feel I am not getting enough pull off the PCV under WOT. I have brand new AC Delco PCV valves and fresh hose, nothing blocked. Was thinking of cutting in a breather but I a couple of the threads implied that one side the PCV sucks and the other it doesn't, not sure why I it would work that way. Seems to me that both the line running to the throttle body area and the other to the manifold.
What I was considering doing is putting a breather element in line between the PCV valve and the intake, with a T that can be capped for street driving but opened for track and autocross events.
Thoughts, examples of other solutins?
Thanks
the car in question has a stock L98 motor, 1990 6sp which is autocrossed regularly.
Engine has been resealed. Performance / power is excellent. However since all the leaks have been sealed I have noticed I pump oil out the dipstick.
I have searched the numerous threads here and other sites, and feel I am not getting enough pull off the PCV under WOT. I have brand new AC Delco PCV valves and fresh hose, nothing blocked. Was thinking of cutting in a breather but I a couple of the threads implied that one side the PCV sucks and the other it doesn't, not sure why I it would work that way. Seems to me that both the line running to the throttle body area and the other to the manifold.
What I was considering doing is putting a breather element in line between the PCV valve and the intake, with a T that can be capped for street driving but opened for track and autocross events.
Thoughts, examples of other solutins?
Thanks
Le Mans Master
Joined: Dec 2002
Posts: 5,270
Likes: 3
From: Seattle Area WA
On my 86 PCV airflow goes:
through the airfilter/MAF (metered)
tee'd off line to pass side valvecover (stock this is on your throttle body IIRC, no PCV)
through the engine crankcase
out through the driver's side PCV valve
into the intake manifold (vacuum source)
90 could be different, or you just have 1 extra valve.
through the airfilter/MAF (metered)
tee'd off line to pass side valvecover (stock this is on your throttle body IIRC, no PCV)
through the engine crankcase
out through the driver's side PCV valve
into the intake manifold (vacuum source)
90 could be different, or you just have 1 extra valve.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Common problem with WOT operation.You have little or no vac on PCV system.
Under normal running cond , air enters pass cover , goes through engine and exits to intake through
PCV valve on drv side cover
@WOT , the fumes travel back up the hose from pass side cover ( which is the inlet air for PCV when you have vac
at PCV valve) to the TB .
Port for that hose is in front of throttle blades so only passing air "suction" ; not true vac
as if pulled from behind the blades like the PCV valve does
At WOT when you have greatest case pressurization , engine is only being vent by tiny 3/8" line with no vac on it
Short of a dedicated pan Evac system , possibly open breathers on each cover to relieve crankcase pressure (temp seal PCV valve ) and clean the mess off the valve covers at end of race?
PCV valve on drv side cover
@WOT , the fumes travel back up the hose from pass side cover ( which is the inlet air for PCV when you have vac
at PCV valve) to the TB .
Port for that hose is in front of throttle blades so only passing air "suction" ; not true vac
as if pulled from behind the blades like the PCV valve does
At WOT when you have greatest case pressurization , engine is only being vent by tiny 3/8" line with no vac on it
Short of a dedicated pan Evac system , possibly open breathers on each cover to relieve crankcase pressure (temp seal PCV valve ) and clean the mess off the valve covers at end of race?
Last edited by rodj; Jan 20, 2012 at 08:03 PM.
Le Mans Master
Joined: Oct 2007
Posts: 9,682
Likes: 3,434
From: Akron Ohio
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How many miles on the car? I would do one of two things. When my '90 got to about 100k miles it started sucking oil through the TB during track days. My solution at the track was to cover the tube on the TB with duct tape and put the hose back on. It didn't suck oil anymore but I pressurized the crankcase enough to blow the grommets out of the valve covers and spew oil all over the engine. I later tried breathers like you mentioned but then the oil comes out the breather and drips and burns on the exhaust. My final solution was to remove the PCV system and plumb both valve covers to a vented catch can. The problem was the rings were worn and allowing too much blow by. Now that you have replaced all yhe gaskets and stopped the leaks the oil is trying to find another way out. It sounds to me like a rebuild is in your future. Anything you do now will just be a band aid fix.
Thread Starter
Burning Brakes
Joined: Mar 2009
Posts: 830
Likes: 6
Thread Starter
Burning Brakes
Joined: Mar 2009
Posts: 830
Likes: 6
On my 86 PCV airflow goes:
through the airfilter/MAF (metered)
tee'd off line to pass side valvecover (stock this is on your throttle body IIRC, no PCV)
through the engine crankcase
out through the driver's side PCV valve
into the intake manifold (vacuum source)
90 could be different, or you just have 1 extra valve.
through the airfilter/MAF (metered)
tee'd off line to pass side valvecover (stock this is on your throttle body IIRC, no PCV)
through the engine crankcase
out through the driver's side PCV valve
into the intake manifold (vacuum source)
90 could be different, or you just have 1 extra valve.
Thread Starter
Burning Brakes
Joined: Mar 2009
Posts: 830
Likes: 6
How many miles on the car? I would do one of two things. When my '90 got to about 100k miles it started sucking oil through the TB during track days. My solution at the track was to cover the tube on the TB with duct tape and put the hose back on. It didn't suck oil anymore but I pressurized the crankcase enough to blow the grommets out of the valve covers and spew oil all over the engine. I later tried breathers like you mentioned but then the oil comes out the breather and drips and burns on the exhaust. My final solution was to remove the PCV system and plumb both valve covers to a vented catch can. The problem was the rings were worn and allowing too much blow by. Now that you have replaced all yhe gaskets and stopped the leaks the oil is trying to find another way out. It sounds to me like a rebuild is in your future. Anything you do now will just be a band aid fix.
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Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
Thread Starter
Burning Brakes
Joined: Mar 2009
Posts: 830
Likes: 6
Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
So your were screwed
Valve in pass side cover not opening because no vac from TB and valve in drv side not working
because no air available from pass side.
At WOT; totally relying on the crankcase pressure to blow fumes pass spring loaded closed valves
Valve in pass side cover not opening because no vac from TB and valve in drv side not working
because no air available from pass side.
At WOT; totally relying on the crankcase pressure to blow fumes pass spring loaded closed valves
Heel & Toe
Joined: Oct 2010
Posts: 19
Likes: 2
From: Roy Utah
http://www.smokinvette.com/corvettef...t=21390&page=2
