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Hello,
I just recently purchased this supercharged 88 corvette, and am running into a crank case pressure issue that I need help with.
the car spewed oil out of the dipstick so I took it to a mechanic and had a full inspection done and the only the issue the car has is that there’s too much pressure in the crank case and to my understanding I need a source for a negative pressure because:
positive + crank case pressure combined with (normally) negative - intake vacuum creates an equilibrium but because this car is supercharged that creates
positive + crank case pressure combined with + supercharged intake pressure causing this issue.
I would like to fix it by removing the pcv tubing and capping the intake side while adding a filtered ventilator to the top of the valve cover so that the engine can safely ventilate to atmosphere.
is this the correct solution and if it is, what parts would you all recommend?
I would make sure that only the drivers side valve cover has the PCV valve and the passenger side is just a clear connection.
Looking at you’re pics, it looks like there is 2 PCV valves.
I would make sure that only the drivers side valve cover has the PCV valve and the passenger side is just a clear connection.
Looking at your pics, it looks like there is 2 PCV valves.
yes I believe they both run to the intake manifold
On my setup I have one PCV valve on the drivers valve cover with a one way check valve. On the passenger side is a vent-no PCV valve T'ed to the throttle body with a one way check valve there. The other side of the T goes to the air filter. I had to install oil catch cans on both sides also. You really need the one way check valves on every vacuum line except to the surge valve.
On my setup I have one PCV valve on the drivers valve cover with a one way check valve. On the passenger side is a vent-no PCV valve T'ed to the throttle body with a one way check valve there. The other side of the T goes to the air filter. I had to install oil catch cans on both sides also. You really need the one way check valves on every vacuum line except to the surge valve.
can I get some pictures and if you have part numbers I would be so thankful
can I get some pictures and if you have part numbers I would be so thankful
On the drivers side the PCV hose goes up front to a catch can, the return hose has the check valve-it has a bunch of epoxy on it after it popped apart on me. The passenger side -the hose on the valve cover is coming from a vent in the valve cover towards the back, goes to the catch can. The return hose is into the T. One side of the T goes behind the engine and over to the air filter. The other side to the throttle body thru a valve that is controlled by a vacuum line, similar function to the purge valve function. All the check valves are just generic that you can buy at any auto parts store. The valve to the throttle body says Rochester vac control with a part number 17087244. I have a few thing apart fixing exhaust leaks right now so things are visible. What SC do you have? The catch cans are also just generic from ebay-sealed, no vents so still smog legal. This setup is working good for me with 15lbs of boost. If I'm going to a track I've made a filtered vent that goes over the oil fill once the screw cap is removed to really vent it, otherwise on the street I don't need it.
Last edited by drive it; May 21, 2026 at 11:54 PM.
On the drivers side the PCV hose goes up front to a catch can, the return hose has the check valve-it has a bunch of epoxy on it after it popped apart on me. The passenger side -the hose on the valve cover is coming from a vent in the valve cover towards the back, goes to the catch can. The return hose is into the T. One side of the T goes behind the engine and over to the air filter. The other side to the throttle body thru a valve that is controlled by a vacuum line, similar function to the purge valve function. All the check valves are just generic that you can buy at any auto parts store. The valve to the throttle body says Rochester vac control with a part number 17087244. I have a few thing apart fixing exhaust leaks right now so things are visible. What SC do you have? The catch cans are also just generic from ebay-sealed, no vents so still smog legal. This setup is working good for me with 15lbs of boost. If I'm going to a track I've made a filtered vent that goes over the oil fill once the screw cap is removed to really vent it, otherwise on the street I don't need it.
i have a pro charger with the MSD stuff, no idea on boost but it feels roughly about as fast as my C5 but the C5 has a 6 speed and the supercharged c4 is automatic. I’ll start looking at the parts you sent and do my best to replicate what you’ve done
So is it tuned for AFR by a separate boost referenced fpr? And timing retard with the msdbtm. And where are you located? So is it the P600b?
min located in Southern California, and unfortunately I don’t know much about the car, although I’ve found a scary red button and a timing retard switch so far. No AFR gauge or boost gauge and I don’t know why
You want an open to atmosphere breather on the passenger side and a check valve between the pvc and the intake on the driver's side. You don't want to blow high pressure air into the bottom end. Tuning should be done to accommodate the un-metered pvc air.
A cracked piston will blow the dipstick out of the tube and oil down the track (or at least make a big smoke show).
yes I believe they both run to the intake manifold
The passenger side valve cover takes in clean metered air from port on throttle body and the driver’s side valve cover with PCV valve sucks out crankcase gases through intake base.
If that is a PCV valve in passenger valve cover, it will not allow fresh air into crankcase.
The passenger side valve cover takes in clean metered air from port on throttle body and the driver’s side valve cover with PCV valve sucks out crankcase gases through intake base.
If that is a PCV valve in passenger valve cover, it will not allow fresh air into crankcase.
this could be part of the issue as I know the throttle body is capped off
You can see in my pics the hose route for the two hoses in PVC circuit. Only driver side has a PCV valve.
interesting, your passenger side goes to the throttle body like someone else said, is that hose not part of pcv system? Because my hose from the passenger side goes to the intake instead, I’ll get some better pictures after I get home and get some sleep (currently finishing up a 12 hour shift)
interesting, your passenger side goes to the throttle body like someone else said, is that hose not part of pcv system? Because my hose from the passenger side goes to the intake instead, I’ll get some better pictures after I get home and get some sleep (currently finishing up a 12 hour shift)
Yes, the hose from passenger side valve cover is part of the PCV system. It takes fresh clean metered air from throttle body into valve cover and the driver side pulls out the air and adds it to combustion air.
I checked again this morning and this is what I found
the two pcv valves do not run to the intake, they connect via a hose under it.
the driver side pcv hose only goes under the manifold cover to connect via a T to the passenger side then they go to this black box (catch can maybe?)
That is totally wrong! That is the air(smog) diverter valve. One line in from the SC-the SC provides air that used to be supplied by the smog air pump. One output exits xtra air to atmosphere-it should be a pipe routed downward. Then outputs to the exhaust manifold and a separate output to the cat converter. The computer controls switching the air to the different outputs.
I can't quite see in that pic, but it looks like one output is going to the air tubes on the headers-the other that should go to the cat converter is pressurizing air to the throttle body and both valve covers.
Last edited by drive it; May 22, 2026 at 04:49 PM.
New C4 owner please help with supercharger issue
