[urq] Too much Crankcase ventalation?

[QSHIPQ at aol.com]

Ben
Congrats on getting it running, missed the actual fix, since I was  perplexed 
staring at the non-run status on my visit earlier this  spring...  WRT PCV, 
by default, on several add on turbo/supercharger  systems over the years, I've 
been initiated fully into this mysterious  dark world of vacuuming 
dynosuar-scum we call PCV.  First, that's a  lot of vacuum!  I thought 14in with my 
re-gifted blue urq was a  lot.  I suspect you are actually creating so much that 
your squeal may be  the seal whistle as it finds more free air source.  Let's 
look at the stock  system, then look at what EFI does to it.
 
The stock urq uses a combined breather/low vacuum setup with a manifold  
valve.  When the urq is not under boost, the PCV routing goes from the  crankcase 
to the head, and then directly into the manifold.  When the urq  is under 
boost, the PCV routing goes from the crankcase to the head, and then to  the igloo 
(PCV valve at manifold is closed).  This allows a mild vacuum  source under 
boost, keeping pressure from building in the crankcase under  sustained boost 
load (trailer/mountain/high GVWR).  
 
Looking at the above, with a stock urq you have a maximum vacuum of  14in at 
idle at sea level (most urq's IME see around 12in - I have the euro  head and 
cam which puts it higher).  Ok, that's baseline, now add in EFI  with the 
stock PCV...
 
What did you do with the breather/low vacuum line with the EFI setup?   My 
guess is that with increase vacuum, you need to increase port size on the  
breather, and possibly decrease port size on the manifold valve.  What  I've 
learned over the years, is that slight changes to designed PCV vacuum  sources can 
really affect how the PCV works or specifically doesn't.  For  instance, many 
times I've seen restrictors inserted into the igloo breather  line, that 
actually caused too much pressure in the system.  The last one I  saw this with on 
an urq, actually blew oil out the turbo seals because the  pressure was too 
high on the gravity return of the turbo oil.  Here, you  are experiencing the 
opposite problem...
 
With vacuum too high, you will overload the breather line capacity, and the  
vacuum in the crankcase and head will be excessive.  You equalized the  
breathing by removing the oil cap, which means you need to either add a bigger  
breather, or add an additional breather until you get the right equalization of  
engine manifold vacuum to engine crankcase vacuum and/or restrict the size of  
the PCV valve ID at the intake manifold.  I tend to favor chasing smaller  
vacuum feed ports to larger breather ports first, because vacuum leaks tend to  
become more significant as the amount of vacuum increases.  To this end,  you 
can replace the PCV valve with one out of a later turbo car (an  upright ball 
and valve type vs the diaphram type the urq uses).  Once  under boost however, 
you need to make sure you have a constant low vacuum source  to keep negative 
pressure in the crankcase, without blowing oil out the valve  cover gasket.
 
Ben, it's a dance for sure, but the very last thing I would do, is go catch  
can.  IMO/E, that's an 'nth' power mod on a full out race car that has  
optimized VE in every other respect.  Or, if you are running really high  boost 
levels, it can increase the amount of air vs oil vapor.  But, as a  general rule, 
I run PCV closed loop whenever possible.  It's easy to run a  catch can, it's 
harder to design a proper sized PCV system.  In my opinion  catch cans are 
mostly used to avoid the harder design of doing it  properly.  Which means by 
definition a catch can would be catching more  than a properly designed closed 
loop PCV circuit.
 
HTH and my .02
 
Scott Justusson
QSHIPQ Performance Tuning
Chicago
 
 
 
 
 
 
 
In a message dated 9/4/2007 3:34:09 P.M. Central Daylight Time,  
benswann at comcast.net writes:
am finally able to drive the Ur Quattro that has  the new engine with
Megasquirt - Yeah!.  Engine is balanced MC-1 with NF  head.  I am now tuning
it, so it will get better and better, but  starting way rich, and trying to
figure creative ways to tune since I don't  have ready access to a dyno.  I'll
probably need to have someone drive  as I make changes to the VE tables, etc..
Ideas?



Anyway, after  my first extended tuning session and the engine was on the warm
side, I  noticed a nasty squeal almost like a loose belt when the engine  was
idling.  I feared the worst as it seemed to be coming from the head  and
sounded a little like a metal machining noise, but went away when I  gunned 
the
engine.  Oil level was good - still on the Havalone break-in  crap.



I pulled the oil cap and the noise went away with a release  of some serious
vacuum.  I repeated this experiment only to conclude  that there is so much
vacuum on the head at idle, that it is probably  evacuating the cam bearing or
something to that effect.  If I left the  cap loose, the noise did not come
back, each time I tightened the oil cap,  the noise cam back in a few seconds.
I have the UrQ PVC hose setup, but so  much is removed of the CIS stuff, there
is fairly much a direct draw into the  Intake manifold and the engine is
pulling a good 18-20 lbs of vacuum at  idle.



So just seeing if there is any solution to this.  I  would expect I should 
have
some ventilation in the cam area, but this is too  much.  Ideas?



Ben
 



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