I think they might be using an oil pan or
oil sump on the turbo. We and other have had a lot
of trouble with oil drain back from turbo's. Particularly
if they are mounted low relative to the engine main oil pan.
Chuck Hurburt went so far as to to add an electric
scavenge pump to the turbo as I recall.
I also see a line going into the Porsche turbo oil pan that might
be a vacuum line. A bit of vacuum down here would help
scavenge the oil vapor from the turbo.
-- Paul Lamar ...No rotor no motor.
Porsche has always used a dry sump turbo approach, pretty much because
they had to. ( the turbos are mounted below 'oil level' and therefore
need to be scavenged) Conveniently, the flat six engine was already
dry sumped for its normal crankcase oiling, so adding a small scavenge
stage for the turbo was easy, schematically.
The 'vacuum line' labelled in the picture is just to normalize the
interior of the scavenge can. A breather. if you will. It allows the
oil to be sucked out the bottom without pulling too hard on the turbo
oil supply line.
As a point of interest, in the '87- 91 Callaway Twin Turbo Corvettes,
we also used a dry sump approach since we wanted to mount the turbo
very low in the car. (mostly for heat vs. fiberglass reasons...)
But without a suitable scavenge pump as part of the Chevrolet engine,
we built a small gerotor pump into the idler tension arm of the
serpentine belt system. The gerotor was about 1.125 inch in diameter,
but since it was spinning at 4 times crank speed, it scavenged the
little tanks beneath each turbo with authority. In other words, it
really sucked.
Reeves
Thanks Reeves. Very interesting.
-- Paul Lamar ...No rotor no motor.
Interresting solution Reeves! Do you ever have a oil backflow problem
with the engine off?
I'm interested in dry sumping my 20B and I'm concerned about the oil
level because the
tank will be located fairly high, (due to the necessity of firewall
locations). Have have you
ever had problems with your little pump due to
_low_ oil flows? Like a
customer that idles a lot.
Since it runs 4X crank I was wondering if you might have to feed it
something to keep the
OD portion of the Gerotor lubed. Thanks for sharing a really cool idea.
It should also show
owners of Calloway Corvettes that you are giving them some excellent
engineering for the
money!
Bill Jepson
No low flow problems, Bill.
My guts tells me there is always enough residual oil in the system to
lube the gerotor, in fact a good indicator is that none of those
systems ever lose prime even after sitting for extended intervals.
But, with a DS tank mounted high, you will have a tendency to drain
the tank and fill the engine, or the sump, pretty easily, in fact,
over a period of weeks of non use. ( You could preflight this level
check as a curiosity on the rate of seepage down due to gravity, I
suppose) But the real way to ensure against it would be to low
resistance check valve in the line from tank bottom to pressure stage
input. If it offered a few 'inches of water' level of pressure it
would be enough to fight gravity, and still not restrict running flow
in that direction. I've always wondered what the right term for that
kind of valve is....
Reeves
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