<<  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

Lynn,

Understood !

Would it be an advantage to have a very shallow sump with a couple of
depressions and pick-ups at the centre of these depressions - rather than a
flat plate?
I'm assuming it would !
George (down under)

 
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