[s-cars] Crank Case Pressure and Turbo Smoke?

[Cody Payne]

Dave and Gang,
    Thanks for the input.  
 
A few notes:
-1) Here is the picture of my Oil Return line.  Notice that it does
flatten out a bit towards the bottom of the slope..not sure if this
could cause the oil to back up in to the turbo?
http://forums.audiworld.com/s4s6/msgs/52685.phtml
-2) I checked the Crank case exhaust to Intake hose yesterday although
the car was not running I did not see a drop of fresh oil in the hose,
compressor housing, or Intercooler plumbing.  So not sure if I am
getting very much coming out of the Valve Cover.  However that could
mean that the PCV's are clogged or not doing their job just causing
crank case pressure.  I guess I could disconnect the exhaust port from
the valve cover and see if I feel any pressure there with my hand?
-3) Dave with that PCV mod (adding a 2nd PCV) sound like a easy test.
This would just prevent positive pressure going in to the VC when the
BPV opens.  Seems easy enough to try out and wont hurt anything assuming
I have the PCV oriented so only pressure can "leave" the VC and not
enter it from the Intake tract/hose
 
Let me know if I am on the right track and if the above Oil Return line
looks suspicious?
 
Thx Guys
 
Cody
 

	-----Original Message-----
	From: Djdawson2 at aol.com [mailto:Djdawson2 at aol.com] 
	Sent: Monday, February 21, 2005 11:02 PM
	To: Cody Payne; s-car-list at audifans.com
	Subject: Re: [s-cars] Crank Case Pressure and Turbo Smoke?
	
	
	In a message dated 2/21/2005 5:16:55 PM Mountain Standard Time,
cpayne at bconnected.com writes:
	
	

		Suggestion; if you have not already made significant
upgrade to you
		crankcase breathing system, do so."
		
		This is really something I dont understand too
well...nor know how to
		alleviate or measure to see if that is the cause
		



	Cody,
	The possibility of excessive crankcase pressure sounds feasible
to me.  On the higher capacity compressors, I have noticed that when
bypass occurs, crankcase pressure can become positive.  The crankcase
breather essentially runs from the crankcase to the back of your valve
cover, and then from the valve cover to the "MAF to turbo" hose.  Your
valve cover is not vented, it is really just a tube through the valve
cover that has no flow to the valve/cam area itself.
	
	When your engine is under load (producing significant boost),
and you let off the throttle... the bypass valve opens.  When the bypass
valve opens, a significant amount of pressure is "bypassed" back into
the MAF to turbo hose.  This also happens to be where the crankcase
ventilation also resides.  I believe that the sudden pressure in this
hose causes a pressure flow back into the crankcase.  This will
definitely cause smoke.
	
	You can very easily (and cheaply) test my theory.  Go to any
decent auto parts store and look through their selection of PCV valves.
Find one with an OD that is the same as the ID of the hose that goes
from your valve cover to your MAF/turbo hose.  These are usually under
$5.  Also get 2 hose clamps.
	
	Cut the valve cover vent hose, and install and clamp in the PCV
valve.  The PCV valve is really just a one way check valve.  Make sure
you install it such that the valve closes any time pressure is moving in
the direction of the valve cover.
	
	I think this may solve your problem.
	HTH,
	Dave