> 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

   Reeves

   I believe the are called "Spring loaded check valves".

   Joel


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