[V8] V8 Crankcase Ventilation (PT/ABH)

Wed Oct 3 10:22:21 PDT 2012

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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