Too much Crankcase ventalation?

Al Streicher streichea001 at
Tue Sep 4 22:47:45 EDT 2007

For some of us who don't understand how to measure "battery drain", could
someone please explain.

-----Original Message-----
From: quattro-bounces at
[mailto:quattro-bounces at]On Behalf Of QSHIPQ at
Sent: Tuesday, September 04, 2007 2:58 PM
To: quattro at; urq at
Cc: benswann at
Subject: Re: Too much Crankcase ventalation?

Congrats on getting it running, missed the actual fix, since I was
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,
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
your squeal may be  the seal whistle as it finds more free air source.
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
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
(PCV valve at manifold is closed).  This allows a mild vacuum  source under
boost, keeping pressure from building in the crankcase under  sustained
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
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,
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
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
breather, or add an additional breather until you get the right equalization
engine manifold vacuum to engine crankcase vacuum and/or restrict the size
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
become more significant as the amount of vacuum increases.  To this end,
can replace the PCV valve with one out of a later turbo car (an  upright
and valve type vs the diaphram type the urq uses).  Once  under boost
you need to make sure you have a constant low vacuum source  to keep
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
levels, it can increase the amount of air vs oil vapor.  But, as a  general
I run PCV closed loop whenever possible.  It's easy to run a  catch can,
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
definition a catch can would be catching more  than a properly designed
loop PCV circuit.

HTH and my .02

Scott Justusson
QSHIPQ Performance Tuning

In a message dated 9/4/2007 3:34:09 P.M. Central Daylight Time,
benswann at 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.
probably need to have someone drive  as I make changes to the VE tables,

Anyway, after  my first extended tuning session and the engine was on the
side, I  noticed a nasty squeal almost like a loose belt when the engine
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
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
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
I have the UrQ PVC hose setup, but so  much is removed of the CIS stuff,
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
some ventilation in the cam area, but this is too  much.  Ideas?


************************************** Get a sneak peek of the all-new AOL
quattro mailing list
quattro at
Watch this space for ads :)

More information about the quattro mailing list