[V8] V8 Crankcase Ventilation (PT/ABH)

[dsaad at icehouse.net]

It's deja vue all over again...

I think I wrote this exact
screed a few years ago!!
Ultimately I ended up replacing the rings -
which cleared (literally and figuratively) things up.
My car did all
the same things yours does - especially the cloud of blue smoke after a
long downhill decelleration.  In fact, the motor would die if I put
the clutch in after a long downhill.  I still have the problem where
if I park on my very steep driveway, I get a big blue cloud on
startup.  The rest of the time I think I am in the "normal"
consumption range. I havent checked it in a while but I suspect I use a
quart every thousand miles or so.  I think of it as a running oil
change :-)

Dave


> 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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