My understanding is this: Once you install an intercooler the PCV air passage is blocked off, rendering the PCV useless, which just builds up pressure inside the crankcase until you blow a gasket. Hence this is why all intercooled 3800'* (that I have personally seen) use a breather on the front valve cover. This way gases can escape the crankcase. In addition to this I've been told adding a breather to an already functioning PCV system just adds unmetered air to the mix, causing high fuel trims.

Thoughts?

i'm so confused since reading this post! got one question!
1. do our cars have a breather, and if they do, where is it at?

It sounds like you're spot on with what you're saying. The best explanation I've found so far was at: http://www.autoshop101.com/forms/h63.pdf

Goes into good detail with pictures. A telling paragraph from the site was:

"Because PCV operation is factored into the proper operation of the feedback control system, problems with the PCV system may disrupt the normal air/fuel ratio balance. A plugged PCV valve will prevent the normal flow of crankcase vapors into the engine and can result in a richer than normal air/fuel mixture."

Which would mean to me that allowing fresh air into the crankcase may result in a lean condition.

All engines using a PCV system have to have some sort of breather. The TPI and LT1 V8 cars use an external hose to connect the valve cover to the throttle body. The 3800 vin C engines used a similar method. Starting with the 3800 TPI (vin L), the breather passage was cast internal to the intake manifold and throttle body. The Series II L67 and L36 also have this passage. If you were to block this passage off and leave the PCV system in tact, there is a good chance you could suck a seal or two into the engine due to the vacuum buildup at lower engine loads.

When the PCV/breather system on your stock 3800'* is functioning normally, the PCV valve will allow "metered" crankcase air flow to enter the intake manifold. This draws a small amount of vacuum on the crankcase. To replentish the "missing" air in the crankcase, air enters the crankcase the only place it can, thru the inlet breather passage in the throttle body, thru the intake, and into the engine. This air entering thru this passage in the throttle body registers in the MAF sensor. If you run an external breather then the PCV negative crankcase pressure gets replentished by unmetered air entering thru the breather.

People like myself who run a turbo (or external boost source) have to block off the integral breather passage otherwise boost pressure could enter the crankcase and blow out engine seals. People running the popular intercoolers under the supercharger typically have to use external breathers because the integral breather passage gets blocked off by the intercooler.

If you are not running an external boost source or a "sandwich" intercooler there is no reason to have an external breather. It adds no performance value to the engine. In fact, adding does present the possiblity of allowing another place for contaminents to enter the engine and get into the oiling system.

Hmmm. Could this be the reason why GM does not have an intercooler as an option?
It would disable the PCV system and put them out of emissions compliance.
I remember back in 1999 they toyed with the idea in a pre production SC & intercooled Buick Regal but it never made production.

So, if I understand correctly, adding a breather to the front valve cover is OK for a supercharged or turbo L67 but not OK for a NA 3800.

Sealed or vented, it makes absolutely no difference to the idle speed on my engine.
Purely cosmetic.....until I get an intercooler.

you probably dont run high enough boost pressure to worry about it. Otherwise GM would have a different system. (how many L67 with blown seals/gaskets ahve you found)???

I'm standing by the belief that you don't need a breather on an L67 unless you are IC'ed.

Hmmmm....this is stupid. It would be very easy to build an IC with the PCV passage. It'* just a hole.

I would have to agree 100%... You would think the money you have to pay for an IC it would be better engineered!

I think the INTENSE IC does not require modification of the intakes so the PCV system should remain intact. I emailed Scott about this for clarification. Most often you will see people having to do this when switching to an LS1 throttle body which does not have the passage for the PCV system. The PCV must be closed off and a breather used in this instance.