Too much Crankcase ventilation? - More

[QSHIPQ at aol.com]

Ben
I'll address this to you since you started it, but Claus and Dave's  
responses are in here as well.
 
First, a look at how the 20vt works.  Indeed there is PCV at the valve  cover 
Dave, at least on a 95.5 S6, I just looked.  It's the little hose  below the 
turbo intake breather hose connection at the back of the  valve cover.  It 
goes down to the vacuum valve at the crankcase, where  crankcase, valve cover and 
intake feed all converge at the crankcase '8  ball'.  According to TST 218, 
during high vacuum (idle) the PCV is drawn  into the intake via the ck valve at 
the intake manifold.  During low vacuum  or boost, the PCV is drawn into the 
inlet side of the turbo via the pressure  control valve.
 
This means that a larger turbo with the same size inlet pipe will have more  
vacuum pulling on the pressure control valve.  It also means that oil  
sloshing in the head and oil sloshing in the crankcase, has a really good chance  of 
getting sucked up at idle, just off idle, launches and at a higher than  stock 
boost level.  Not sure why audi mounted all this so low on the block,  it's 
really conducive to sloshing issues of both the block and the head  (guessing 
the head causes more oil issues than the block, since that 8ball  crankcase 
design on the block has been around a long time without issue).
 
WRT what to use for a modded/improved PCV, I would highly suggest the supra  
twin turbo app (don't forget the gasket) 1993-1998.  It operates per the  
website I provided, and it has a really good turbo shutoff action on it.   And, 
discounted, it's less than 10 bucks.  I noticed that the Mustang  supercharger 
boys use this valve as the 'standard' as well.  
 
For hookup on your 10vt Ben, I would consider putting this valve in place  of 
the stock urq pcv valve, and mount it above the valve cover somehow.  I  
would think you could machine up a simple block that would tie all this together  
with the stock system.  Since the supra twin turbo uses a really high  
compression ratio, I'd bet the match to the orifice of that PCV valve would be  
really good.
 
What may screw all this up, is the amount of vacuum present at the turbo  
inlet.  That's pretty key to making sure the breather is acutally breathing  air 
vs fighting an alternative vacuum source.  Claus, wrt octane vs oil  vapor... 
In a properly designed PCV system, there shouldn't be enough blowby to  make 
this significant.  And if you read the site I posted, if 70% of that  vapor is 
unburnt HC, you aren't affecting octane much at all.  IME, running  back to 
back PCV connected vs not, there appears to be no significant difference  in 
dyno output (read: just another run can result in the same change).
 
Martin, PCV is one of my interests along with the black mysteries of  Torsen 
operation.  Call me PCV boy if you want, but I really believe there  are very 
few that really understand how it works, more  specifically, how to work it.  
I don't see closed loop PCV as a bad  thing, and both Eaton and Magnuson 
advocate running PCV closed loop to carbon  treat the blades of the SC and put a 
coating of deposits in the plenum to screw  clearance.  I don't see why this 
theory also wouldn't hold true for a turbo  as well.
 
Scott Justusson
PCV Boy formerly known as Torsen Boy
'94 Landcruiser Supercharged with modified PCV 
 
 
 
 
 
 
 
In a message dated 9/5/2007 3:19:48 P.M. Central Daylight Time,  
benswann at comcast.net writes:

Thanks  Scott,



This is helpful in furthering my understanding.  I  thought I knew what a PVC
valve did and how the system functions - or is  supposed to.  I think by the
end of this I'll really understand.   Until the next time that is.



So any recommendation on which  valve to use - if you go to FLAPs there are at
least 50 different versions  of valves and even more variation when you get
into model, port size and  orientation.  Some are simple check valves and some
are apparently  much more.



We have to presume that I no longer have the proper  remnents of the UrQ 
setup,
and that the restriction would be significantly  different.  I checked out the
early TQ implementation and it works  because there is just a slight venture
vac. Used inside the metering  box.  With speed density, no such  port.



Ben


 



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