Date: Wed, 27 Mar 2002 02:42:47 EST
Reply-To: FrankGRUN@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Frank Grunthaner <FrankGRUN@AOL.COM>
Subject: Windage Trays and Lubrication Issues (Air and Water Cooled)
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Stan and Matthew,
It is really quite frustrating that modifications such as K&N air cleaner
substitutions are pitched to the masses and quick and cheap power increases
(actual power increase is around 0.05 to 0.12% in an otherwise unmodified car
- difficult to measure!) while addition of a windage tray can return 5 to 10
"free" hp. I say free because no aspect of the engine combustion dynamics or
output stresses are increased. In fact internal stresses are actually
decreased. Your comments (quoted below) are essentially correct, but there is
even more to the story.
The oil in the sump and where it goes are critical issues for power output,
fuel economy and engine longevity. As Matthew points out, the crankshaft acts
as a gigantic egg beater. At very low rpm, the crankshaft is just agitating
the oil as it throws it around. But as early as 1500 rpm (depends on the
viscosity and film shear strength - which are in turn functions of
temperature and parent oil stocks) the oil wraps around the crankshaft much
like cotton candy on a spool. The crank can become a liquid encapsulated
object with slots cut out for the connecting rods and the main journal webs.
With higher rpm the oil is so strongly aerated that it becomes a milky foam.
This oil foam now becomes hard to pump with the typical gear pump, oil
pressure drops and crankcase pressure soars. Oil is thrashing on the cylinder
barrels, undersides of pistons - you name it .... and the reserve level
accessible to your oil pump pickup falls. Add moderate braking or 0.5G turns
and there is no oil under the pickup. Prescription for disaster or at least
short lifetime between bearing replacements.
There are several solutions (all mostly developed in racing, since these
effects get worse with higher rpm and temperature).
1. The best solution is a dry sump oil system. Here an external pump with
high capacity (actually organized into several pumping stages and externally
driven) is used to evacuate all the oil from the oil pan as it falls down
from feeding the galley, pistons and mains. The oil is removed from several
areas in a very small volume pan and pumped into a holding reservoir. The oil
is then degassed and pumped back into the engine. Dry sump engines also run a
higher quantity of oil (often 10 quarts or more). Solution good but
expensive. A Dry sump system for the VW I4 engines runs about $1400, and
costs about 10 hp (because of the work required to drive the multiple high
capacity pumps).
2. Carefully adjust the oil level. Cheap, can work, could be dangerous. If
you keep the mean oil level below the crankshaft arc, and above the oil
pickup tube inlet, and refrain from adventure, you can minimize the whipping
whirlpool. It will still be there, but less oil will be captured. Careful
measurement of oil temperature as a function of the static oil dipstick level
will show the onset of this problem. Unfortunately, that onset is far below
the factory recommended level (often 1 to 1.5 quarts below). The corollary
here is that if you overfill (by as little as 0.5 quarts), you can seriously
drop oil pressure, increase oil temperature (the aerated oil acts as a
thermal insulator and minimizes the thermal exchange in the oil cooler) and
blow out the crankcase seal with excess pressure.
3. Add a windage tray. A good windage tray provides a barrier between the oil
in the sump and the crankshaft lobes minimizing the amount of oil that can be
whipped up by that flying crank. This eliminates the work done by the engine
in overcoming the frictional mass and drag represented by the sheeting oil
(worth about 5 hp in the VW crankcase. In addition, oil pressure will be
higher, temperature lower and lubricity higher because of the lower level of
dissolved gas. However, there are still sheets of oil clinging to the crank.
In a good windage tray, like the VW one for the water-cooled inline 4
cylinder engines, a set of cutters (or scrapers) are formed into the tray and
run at a gap of about 1 mm from the crank lobes. The opening of these
scrapers is oriented so crank rotation is towards the scraper mouth. These
scrapers literally scrape the excess oil sheets from the crank lobes just
like a clay potter shapes his work on the rotating table.
3A. Many professional engine builders find that the functions of windage tray
and oil scraper should be separated and they use thick strong steel scrapers
to run with a 0.010 inch clearance to the crank. These are followed by a
windage tray with the extensive use of screen over open return paths. This
screen deaerates the oil before it drops back to the holding sump.
But this still doesn't treat the oil sloshing caused by starts, stops and
turns. With a boxer engine, these issues can become critical as large amounts
of oil can go to the pushrod tubes and the cylinder barrels.
4. This is handled by the use of baffles in the oil pan and, in some designs,
by trap doors which protect the area around the oil pickup tube entrance.
So, the best solution for the I4 crowd (Vanagons) with the engine mounted at
the Golf angle is to buy the windage tray (I've posted part numbers and
prices in the archives - VW dealer is around $90, but internet prices go as
low as $29). It includes a reusable rubber gasket. You will need longer
bolts. 1 hour operation including cleanup. I would also add a baffled oil pan
by Shrick. Aluminum and around $250+.
For the I4 crowd at the diesel mounting angle, buy the windage tray (note
there are benefits here for gas, diesel or turbo). Your diesel pan has two
small baffles to stop front to back or back to front oil movement. I find
this inadequate. As part of my turbo Audi 3A I am building a modified oil pan
with an internal hexagonal core. The core has 1 cm open zones and is 2 cm
thick. I am mounting it 1 cm above the pan floor with openings for a revised
oil pump pickup. On top of the hex core, I have mounted a 1 mm. open mesh. In
laboratory tests, the oil moves freely under the core to replenish the oil
pickup, but it doesn't slosh since its constrained within the hex cores
vertically. I have also prepared oil level sensors for the pan and will
calibrate the optimal oil level, probably reducing capacity in the pan by one
quart. I'm also adding the dual oil filter system with external
thermostatically controlled oil cooler from the Audi 5000T. Also keeping the
VW coolant to oil heat exchanger. I will make plans and drawings available
when I'm done for anyone who wants to fabricate their own.
For the air cooled crowd, the installation of the windage tray is harder
since it involves a case split. But I would add the 914 part at the first
opportunity. But there is another nice trick. (probably wont work with the
2.0 Air Cooleds but a clever man with time (is there anything else on the
Texan landscape???) One could add a 2.5 quart sump extension from the type 1
engine placing the oil pickup down in that extended sump. This will do two
things at least. First, it will reduce the engine case clearance by 3 inches.
I think this is now the lowest engine point, but only about a 1 inch
reduction in ground clearance. Second, If you keep the same amount of oil in
the crankcase, this will drastically drop the oil level (helps the windage
tray) and the small central fill will eliminate sloshing issues.
Just one more point. You can see it all! As I reported some time ago, I have
placed a borescope in the crankcase and watched all hell break loose in the
RV engine I'm currently using. It is my intention to video tape the results
as I calibrate optimal oil levels on the Turbo 3A, and "field test" the
baffled diesel pan.
Sorry for the length, got carried away again.
Frank Grunthaner
On Tue, 26 Mar 2002 06:57:28 -0500 "G. Matthew Bulley"
<gmbulley@BULLEY-HEWLETT.COM> writes:
> I've wondered the same thing. Having ripped apart and re-built a
> bunch of 914/912e motor, I was a little shocked to see no windage tray in
> the vanagon.
> My understanding of the function of the tray though went beyond just
> oil "sloshing" around, but was more to prevent the upper surface of the
> oil from forming "fans" of oil that followed the crank throws.
> These fans not only slowed the crank (if ever so slightly) but also
> created tiny foam bubbles in the oil, which essentially dropped the
> oil pressure/viscosity at the bearings. Why VW would eliminate it, one
> may never know. >>
In a message dated 3/26/02 6:35:37 AM, wilden1@JUNO.COM writes:
<< I would go along with your "fans" theory.
There is a hell of a lot of things going on in the internal engine
chamber that we don't even conceive of and will never be privileged to
see.
Stan Wilder
