xr4tic

basically, I'm running a tube from the inlet about 1/2 to 3/4 ways down, then fill it with stainless steel scrubber pads.

This should trap the oil in the bottom, but still allow you to run the air back into the turbo inlet.

I'd leave the PCV valve in there, it operates under vacuum only, but that's where you spend a majority of your time.

dingster

The issue when operating in vacuum is you'll pull in unmetered air throught the catch can breather. Unless you put a check valve in the line going to the catch can.

xr4tic

where it goes back into the intake pre-turbo.

Audiboy

During idle and cruise, there is very little blowby produced. So, a small amount of vacuum in the crankcase is required to help regulate the flow of blowby out of the crankcase and into the engine. Too much vacuum can cause seepage of the mixture through the rings and lower effective compression ratio as well as cause the engine to idle and cruise erratically. Oil can only be seeped through the PCV lines. At high loads, high rpms, there is a lot of blow bly produced. Hence, vacuum level is increased because the net result is still some small amount of pressure. This is when a vacuum pump is effective to keep the crankcase out of pressure.

This is why the turbo Audis have that 'PCV valve' between the intake piping and the crank vent. Without it, there may be excessive vacuum when not needed. But when a person chips the car, then that system was probably not designed to accommodate for the extra 'vacuum' caused by the more demanding turbos.

Audiboy

whadayamean illegal? officer, that's for my airconditioner. That filter thingy is for fresh air

xr4tic

which one are you talking about? The one pre-turbo, or the one between the intake manifold and the crankcase?

The one between the manifold and crankcase is only open when there is no boost in the manifold (we'll call it PCV #1)

The one from the turbo intake to the crankcase (PCV #2) should only be active under boost. As air is sucked into the turbo, then a vacuum is created in the turbo intake tube. More boost = more vacuum. How much vacuum, I don't know. It's less than what the engine produces while cruising, maybe 4-5 in. Hg.

From a performance standpoint, you don't want any vacuum in the turbo intake pipe, it raises the pressure ratio of the turbo, causing higher shaft speeds and more hot air.

It's times like this when I wish I had a Magnahelic differential pressure gauge

Audi2ptzero

I dont think that pump is moving the same abouts of CFM like a big turbo will. Our turbo might be causing a much higher vacuum at the crank case breather tube.

Alpha7

and a catch can "should" eliminate this?

xr4tic

which is, what, 1.5" or so?

I'm running a 3" tube, you might run even larger.

1.5" = 0.5625 sq in.
3" = 2.25 sq in.

Assuming same length and temp, the pressure/vacuum will be 4x less in the bigger intake tube (P=VT)

So yes, we're flowing more air, but not 4x as much, so we will have less vacuum in the intake tract (pre-turbo) than factory.

I'm not saying we should run a vacuum pump, as I don't think it would benefit our cars at all, but I am saying that big turbos don't necessarilly mean more vacuum.

xr4tic

more than likely it's just the crankcase breather sucking oil in.