[urq] Too much Crankcase ventalation?
benswann at comcast.net
Wed Sep 5 00:31:14 EDT 2007
Thanks for all the replies. Before going further, it would be good to know
more about the engine:
The engine installed in '83 Ur Quattro is MC-1 rebuilt with align-bored
block/crank with 1 size-over main bearings, piston assemblies balanced to
nearest gram. Reworked NF head 42I 38E valves and stock MC-2 cam has external
aux. water manifold. Intake manifold and throttle body are from WX engine,
dual-piece exhaust manifold, UrQ downpipe to 2.5" exhaust with free-flow cat.
K-24 turbo, Bypass valve is oriented to blowoff to turbo intake after filter
and forced air intake is being fabricated to fit car. Using stock UrQ
intercooler for now. Engine is being managed by separate ignition and EFI
computers - MAC-14 with dual knock sense ignition and most CIS components
deleted, and Megasquirt V2.2 EFI with MSExtra code pushing fuel through 38lb
injectors (for now). Engine is mated to 5000 Quattro transmission using
single-mass 3B flywheel setup. Engine has baffled oil pan from 7A.
Frankenmotor indeed, but intention is to put together a durable high-rev. 10V
I5 engine that fits car well and retains original look/layout as original
OK - back to the XS crankcase/camcover vent issue - this is surely what it is,
and Scott helped bring it to light with his questions. I'd rather not design
and implement a catch-can system yet although it is something possibly to
consider if I push boost over 2.5 bar. I would like to know how I can
regulate things so it just isn't trying to suck the outside in at idle or blow
insides out at full boost - slated to be 2.5 in the near future, but need to
do basic tuning first.
In answer to Scotts ?'s below re. how it is plumbed, it seems I my have things
a bit too simplified right now and I would not even consider present hookup to
be "PVC". Basically there is direct connection using a stock hose between cam
cover, intake manifold and crankcase. So I surmise that whatever manifold
pressure is, it is the same inside the camcover, and crankcase as well. Big
oversight I suppose or more like, just getting things to work as they should
after the car has been down for nearly a year.
As I explore my boxes of doodads and valves, I'd appreciate entertaining any
good suggestions on a simple means of having just a little vacuum in the
crankcase and cam area when under negative pressure and very little if any
postive pressure in the cam/crankcase area when under boost. Or perhaps there
should be just a slight bit of pressure made inside the engine - blowby etc.
that is allowed to vent, but be recovered "gracefully" into the intake. This
engine is new and should be very tight. The noise goes away when vacuum is
relieved in the cam cover area, so hopefully not to difficult..
Catch can recovery system is not outside the question of future mods, but
certainly outside the scope for the immediate needs as best as I can tell.
TIA for suggestions even on how to make a simple catch can and drainback.
From: QSHIPQ at aol.com [mailto:QSHIPQ at aol.com]
Sent: Tuesday, September 04, 2007 8:58 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 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
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. 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
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 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
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
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
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
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
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
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, 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
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. I'll
probably need to have someone drive as I make changes to the VE tables, etc..
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
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
some ventilation in the cam area, but this is too much. Ideas?
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