I recently found oil at the front of my manifold when changing the throttle body. I posted this and heard that the PCV valve or crankcase(both) need vacuum from the intake to operate correctly. Dan can you give us some insight into this and how you deal with that?
Yes, the PCV system needs vacuum to work correctly. The crank case does not need vacuum, however you definitely dont want any positive pressure (leaks). It is true you can pick up a few HP with some vacuum, however, a PCV system will NEVER do this anyway, as the only time it would matter is WOT, and there is no vacuum in the manifold to speak of at WOT anyway, maybe 1-2" tops... nill.
The PCV system is a tree-hugger solution, thats all. It keeps oil vapor out of the atmosphere, end of story, no other purpose. On the downside, this oil vapor can lower octane, it gets oil all over your intake system, and it cakes your combustion chambers over time. Its really best to get it off on these cars, especially if you are running on the track where the oil is being sloshed through the PCV system regularly. For reference, the manifold connects to one cover and to a metered orifice in the cover. The intake connects to the other side to a wide open port. This keeps crank case pressure close to zero with good flow-through, as the wide open intake side has no problem balancing out the pressure as it can flow much more. Connecting the hoses backwards is NOT good, it will put close to 20" of vacuum in the crank case at idle, and such in large quantities of oil under load.
In most Big Power cars, the solution is smple; disconnect the PCV hoses at the manifold, intake, and valve covers, plug all ports, and add some type of stand alone, separate breather system, and your done.
Another BIG issue is on cars with Paxton Blowers and some TT cars. The installers leave the PCV system, add a PCV valve to the Passenger side between the manifold and cover, and call it a day. Sure, this keeps manifold pressure from entering the crank case and causing a bigger issue, but its also one less place for crank case pressure to escape (on a system that by design already has more blow-by then stock!), increasing the flow through the single PCV hose left. this increases port velocity, carrying with it more oil, and those systems eat large quantities of oil through the front end of the system.