Too much Crankcase ventalation?
streichea001 at hawaii.rr.com
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.
From: quattro-bounces at audifans.com
[mailto:quattro-bounces at audifans.com]On Behalf Of QSHIPQ at aol.com
Sent: Tuesday, September 04, 2007 2:58 PM
To: quattro at audifans.com; urq at audifans.com
Cc: benswann at comcast.net
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
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
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
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
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
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
QSHIPQ Performance Tuning
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.
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?
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