Originally Posted by 1Bear

Below is a write up from a gentleman on the SilveradoSS site and I would imagine it would help several members here as well. One item to note is the usage of a PCV made to see boost. It's a little lengthy, but I still recommend people read it.

This last week I've been researching and ordering a TON of PCV valves trying to find one that incorporates a built-in check-valve so boost pressure is not allowed to enter the crankcase. You gotta be a man free of embarrasment to stand at the Oreilly's counter and blow through a bunch of PCV valves as the parts guys are staring at you. Anyways after looking at lots of aftermarket and OEM pieces I have found ONE that for sure seals completely, the Ford OE PCV valve on the supercharged T-Bird, available only at the Ford parts counter as FoMoCo PN E5ZZ-6A666-A for $10; you must get the actual OE FoMoCo valve, the aftermarket Autolite equivalent does have a check valve but WILL NOT seal out boost. I have read that the OE PCV valve used on the Toyota Supra is also a positive one-way PCV valve but I haven't ordered one to give it a test. The FoMoCo valve is a direct replacement on the '03+ LS motors.

At present our recommended PCV system configuration for FI/nitrous-equipped LS motors is:
1) replace the empty OE PCV valve with the Ford one;
2) install a catch can between the PCV valve and the intake manifold;
3) remove the fresh air PCV hose (passenger valve cover) and cap both the valve cover and throttle body nipples;
4) use a breather-equipped oil fill cap, allowing fresh air for PCV under vacuum and blow-by venting during boost.

These 4 steps positively remove any chance of oil vapor entering the intake manifold provided your catch can is up to the task, and it can all be done for 100-150 bones. This is an essential mod on ANY forced induction or nitrous engine to prevent increased detonation risk due to oil ingestion; on NA motors this will keep the intake manifold and valves from totally gunking up with tar deposits.

Installing a catch-can between the PCV valve and the intake manifold is a common mod in almost all gearhead circles; but that's only a job HALF DONE - what most don't realize is the PCV system REVERSES FLOW DIRECTION at WOT on a N/A motor, to be exact the ONLY setup where the PCV circuit will not reverse direction is on a positive-displacement blower (Radix/TVS) where the PCV valve is plugged into the intake elbow, just behind the throttle body and ahead of the rotors themselves (there is always significant vacuum available there). Because of this reversal of PCV flow, instead of crankcase gasses being sucked into the engine via the PCV valve, the PCV valve will temporarily be admitting fresh air and crankcase gasses enter the intake manifold through the throttle body nipple, and the problem will be made worse if there is excessive blowby pressure.

If you ever wondered why the hell the back of your throttle body looked like the Exxon Valdez spill, now you know why - because during WOT the factory PCV system reverses and oil vapor pours in from the passenger cover. Likewise, on a turbo/centrifugal application the boost pressiure in the intake manifold is transmitted via the PCV plumbing and pressurizes the crankcase, blowing oil vapor out every gasket & seal & ejecting the oil dipstick, and the bottom-half of the motor gets nasty looking and begins leaving drip spots everywhere you park...

DO leave the PCV system installed and functioning, without it your engine oil life will only be 1/3rd of normal and your engine wear will go up significantly due to increased crankcase contaminants.

Mr. P.

From what I read, this is how you have your PCV system plumbed right now:


And here is what is happening when you mash your foot to the floor:


At a minimum, I would install the Ford SVO Motorcraft PCV valve, like so - you'll still be feeding blow-by into your compressor but at least you'll stop pressurizing the crankcase, and it will retain smog-legality:


If you want to do this setup and be totally emissions-legit you can use a second catch-can instead of a vent on the passenger-side of the motor, but you need to use a large capacity catch can like the Lingenfelter unit or similar (uses 5/8" or 3/4" hoses). You HAVE TO USE A SECOND CATCH CAN, whoever thought you could tee all the crankcase plumbing into one catch can has not realized that doing so just eliminates any draft/crossflow in the crankcase i.e. doing that stops all PCV action - check it for yourself, draw a diagram and you will see what I mean. Here is an emissions-compliant catch-can install which will still keep oil out of the intake, remember the second (fresh air) catch can must be high volume to handle the high-RPM blowby:


Now, if you want to remove ALL chance of oil ingestion, you might consider re-plumbing and adding a vent:


And the operation of the same setup under boost (not emissions legal because of the vent) -

Originally Posted by JCunningham

I wish the pics still worked