[V8] V8 Crankcase Ventilation (PT/ABH)

[Paul Jager]

Sounded to me like trying to work around a f - - -  up engine with valve & 
ring blow-by, poor valve stem sealing, just an old crusty (as in rubber 
seals) oil burning beast.

Having said that I gather crankcase ventilation has been the scourge of 
engine engineers, including the Porsche 928GTS motor which has unforeseen 
issues with oil consumption as well, I believe due to pre-ignition using 
less than 94 octane fuel, and under hard acceleration. Also directs oil 
vapors into the air intake due to elevated valve/head or crankcase 
pressures. Not sure which, don't really care, just add a liter of oil every 
3-4 tank fill ups. the S4 motors did not have this issue but they were rated 
less HP (lower compression ratio, octane spec).

PS -just got this month's Excellence magazine you can see the 90 Audi V8 
engine in a Porsche 965? prototype. I always said the Audi V8 is a Porsche 
backwards (end for end) both in configuration and "market" desire!


Paul aka - '93 Verboten.




-----Original Message----- 
From: Scott Justusson
Sent: Wednesday, October 03, 2012 10:22 AM
To: CavalloGT at gmail.com ; v8 at audifans.com
Subject: Re: [V8] V8 Crankcase Ventilation (PT/ABH)

Finally!  Good start on the track to improve PCV.  I've done quite a few PCV 
mods over the years, including to the v8.  I suggest that the real answer 
will be to use a standard PCV valve and eliminate the rear hose entry on the 
DS valve cover.  I'm convinced from day 1 that PCV on the v8 was a poorly 
designed afterthought.  Not sure it's all that much better on the I5 cars 
either, btst.  IMO/E there are two problems with the PCV system in the v8. 
Non regulated vacuum, and no protection from sloshing on steep declines, and 
sharp acceleration.

IIRC, I've seen some Audisport engines that actually had proper and common 
valves fitted to both  valve cover tops.

Good work, and a good start down the road to a fix here.  I really doubt the 
mesh in the valley cover will do much without revising the vacuum source, 
and or making a step plate design that prevents a direct flood of the air 
pickup.

Good post!

Cheers

Scott J
92 v8 4.2 ABT Chipped







-----Original Message-----
From: Professor GT gmail <CavalloGT at gmail.com>
To: v8 <v8 at audifans.com>
Sent: Tue, Oct 2, 2012 8:52 pm
Subject: [V8] V8 Crankcase Ventilation (PT/ABH)


We all know the CV (crankcase ventilation) system on these engines "blows"!
Really, the poor design of this system literally blows oil into the intake
stream as it does not have good separation/condensation characteristics.

Not a rant, just a fact.

So, in replacing the engine in my 91 Automatic car (engine going in this 
week) I
decided to do some experimentation with trying to improve it. Ultimately, I 
fear
the only way I will see marked improvement is with the addition of a
"catch-can",and possibly a PCV valve, but I don't want to go there unless my
first attempt (revision 01) doesn't yield the results I'm looking for.

The valley cover (the "labyrinth" as its called in the manual) does not have
much of a labyrinth to it at all, hence the propensity to allow excessive
amounts of oil to be drawn into the intake.

If you study the flow of the system, there are two main paths for vapors to 
take
on their way to the intake manifold:

1: when the throttle plates are closed (idle), vapors flow through the very
small hose at the back of the intake. It's the small hose that loops over 
the
intake where the air box connects, from the labyrinth on the left, to a
restrictor nipple on the right rear of the intake.

Just behind this port on the left side of the labyrinth is the large port 
that
connects to the left side cam cover. This connects the crankcase (blow-by 
below
the piston rings), to the cam covers (blow-by past the valve guides). The 
other
large and very pricey hose that rounds out the picture is the one that 
connects
the two cam covers together, to balance out crankcase blow-by pressure.

2: this path is through the large hose that goes from the front of the 
labyrinth
under the intake, to the throttle body. This path is used for everything 
except
closed throttle, and is of course a higher flow volume path.

Now, let me digress a bit: My stick car behaved as follows:
A) Let it idle for a bit and then immediately upon tipping into the throttle 
the
blue clouds begin!
B) After a long deceleration, upon giving it throttle, again blue!
In fact the mountain I live on is a .9 mile stretch from my house to the 
main
road, and its all downhill, so the throttle is closed 99% of the way down. 
When
pulling away from the stop at the bottom, you got it,  I'm the "bug man",
emitting clouds too thick to see through.

Okay, I concede this is symptomatic of a wheezing engine in need of repair, 
but
to a great degree, the CV system is a large contributor to this mess as 
well!

So lets analyze the situation for a moment. Under idle/decel, engine vacuum 
is
high. The small right rear port is the only one open to intake vacuum. So,
crankcase vapors, and lots of lubricating oil that could not properly drain 
back
to the pan, get sucked through this high vacuum port. This oil puddles on 
the
floor of the intake as even though vacuum is high, velocity through the 
runners
is low.

Upon opening the throttle, the increase in velocity then is able to pick up 
this
oil and pull it through the combustion chambers. The latent oil that was 
picked
up at idle and was coating the exhaust now also has the oxygen (with an open
throttle) to burn off at a much  higher rate: a perfect storm if you will to
spray the neighborhood for bugs! LOL!

The objective is to prevent, as much as possible, oil from being drawn up 
into
the intake. It's funny, because the CV system is designed purposefully to 
draw
IN crankcase vapors so they CAN be burned, versus venting them to the 
atmosphere
ala the days of the old "road draft tubes", prior to the early 60s and the 
start
of PCV (positive crankcase ventilation) systems, the very first emission
control.

Now, without pics it's hard to explain, but under the labyrinth sits a 
separator
plate. This plate (a piece of formed - stamped sheet metal), has the job of
being a baffle of sorts to separate the connection of the crankcase and cam
covers, to the labyrinth and the ports which feed vapors to the intake. Both 
the
labyrinth and the plate have to work together to separate these sections, 
feed
vapors, and try to condense oil from the vapors before they are fed to the
intake, and allow drain back to the oil pan.

One of the primary ways that this is done is through a complex of passages 
that
force the gasses to twist and turn about, so that condensation, AND drainage 
can
occur, and therefore theoretically only the finest of vapors gets drawn back
through the combustion chambers.

Funny, upon closer inspection I expected to see this maze of passageways in 
the
so called "labyrinth", but NOT! I think that must have been the point when 
the
Fräulein  distracted the engineer and things went awry!

This in my humble opinion is the biggest shortcoming with this system.

What I have done is used a material that should help separate these distinct
areas and allow better filtration and condensation of the oil in the gasses.
What remains to be seen is if it will allow adequate drainage of the
condensed/filtered oil back to the pan.

If not, this is where the catch-can and PCV valve would come into play. But, 
one
step at a time.

Ultimately, the addition of a complete PCV system may be what's needed, as 
the
PCV valve itself, by design is a flow regulator controlled by engine vacuum.
This would allow proportionally correct amounts of vapors to be drawn into 
the
intake based exactly on only what's needed.

For now, I added the stainless steel "filtering" material under the 
separator
plate in the valley, through the large hole in the center of the plate, as 
well
as up into the rear of the labyrinth where the small idle flow restrictor is
located. This is important as vapors off-idle to the large hose at the front 
of
the labyrinth are drawn through this point also. So this should cover 99% of 
the
vapors.

We'll see how well this first revision works before we go any further, if
necessary. The spark plugs in this donor engine tell me that the engine is 
in
pretty good shape, so I didn't bother taking any compression or leak down
readings before yanking it out. I do plan on doing that for baseline 
purposes
once it is in and running.

More to come.


Thanks,

ProfessorGT
(Sent from my iPhone4)
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