<<  Lynn,
 > Another thing I don't understand is - with a flat plate engine sump how
does
 > the scavenge pump keep primed without a sump to hold some oil. It just
seems
 > it will start sucking air at anytime ( considering attitude) and lose
prime.
 > George (down under) >>

The oil tank is mounted so that the oil level is higher than the pump. Oil
seeps through the pressure side of the pump and through the bearings to fill the
engine to the same level as the tank. How much side clearance is built into
the pump controls how much time is involved in that process. It could take a
week, or several months.

That is the long term storage answer. In the short term, the pump sections
are over sized by a very large factor. Although the pump elements would could
never get completely dry, even if they could, on startup, the scavenge section
(two pumps both larger than the pressure section) will evacuate the engine and
return all of the oil to the tank in just a few seconds. After a winter of
inactivity the race car will, on startup, have a hesitation of a second or less
before the oil pressure gage snaps to attention. The unprimed pump idea is not
a factor. Each of the three rotors in the dry sump pump are on the order of
six times the volume of both rotors in the stock oil pump.

In operation, the scavenge section is processing mostly air, there being only
the amount of oil available that would have been in the engine had the stock
pump been running at the same pressure. So the dry sump pressure section can
deliver no more oil than the stock pump for any pressure and temperature. The
flow is controlled by bearing clearance in both cases. At idle the oil pressure
could be quite a bit higher because the pump volume per revolution is very
much more than stock. You can also change oil pressure by adjusting the relief
spring screw, or changing pump RPM with a change of pulley tooth count.

Any oil pressure at idle is fine. Flat out 75 pounds with stock bearing
clearance through 8,000 RPM. I have 100 PSI from off idle (80 PSI) through 9,600
RPM. That with racing bearings and additional clearance beyond that. With the
stock pump we would start down the straight away at 85 PSI and at the end of the
straight be down to 70 PSI. Mostly oil foaming, and adding a ton of heat to
the oil very quickly.

Lynn E. Hanover

 
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