[urq] Too much Crankcase ventalation?
djdawson2 at aol.com
djdawson2 at aol.com
Tue Sep 4 21:57:57 EDT 2007
I would agree that the noise you are hearing is air being sucked past seals.? Idle = high vacuum = noise.? Revs higher = low/no vacuum = no noise.
I guess recirculating crankcase gasses is an option, but I don't see it as a requirement.? A catch-can is an OK solution, but if you use the car aggressively, it will fill fast.
Even an AAN engine, with its windage tray, will push a very large amount of oil through the breather system during an aggressive launch.? No good.
I don't know if I'd want to make a project out of properly sizing the breather system.? To me, a good solution involves a breather device that allows the oil to return to the crankcase.
If you've built an engine with serious performance potential in mind, no matter how good the system works, you're going to be pushing a lot of oil through it... not just gasses.? To me it was only important to properly vent the crankcase, and return the out of control oil flow back to where it belongs... the pan.
Unless you redesign around some of the limitations inherent in the stock oil supply system, I think that a PCV approach will always leave you with oil in places that you don't want it... FWIW.
Dave
-----Original Message-----
From: QSHIPQ at aol.com
To: quattro at audifans.com; urq at audifans.com
Cc: benswann at comcast.net
Sent: Tue, 4 Sep 2007 6:58 pm
Subject: Re: [urq] Too much Crankcase ventalation?
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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