Has anybody seen any evidence of oil pump cavitation
at RPM's greater than 4000 RPM?

-Richard wrote:

Since the oil pump is a displacement devise, it can not cavitate,

in

principle. However, if the intake is restricted to the point where

the

suction pressure is getting low enough for the oil to boil, it can

show

symptoms comparable to cavitation. Is that possible? I don't know.

It is

certainly easier to create cavitation in a restriction on the

pressure

side

of the system. We used cavitation for fuel flow control by

inserting

ventury

restrictions in the fuel line.
May be I am overlooking something here.

Richard Sohn
N-2071U
unicorn@gdsys.net
www.gdsys.net/WWWmembers/unicorn/-

Richard can you set up a stock oil pump and see if it can pump clean

oil

with out air at 6000 RPM? We have had one report wherein it was

claimed

the output of the pump was converted to froth above 4000 RPM.
I find that highly unlikely but it won't hurt to check.

Paul Lamar

Hey Paul welcome back, it has been rather quiet in e-mail land.

Am I missing something here, isn't the oil pump geared to one third

e-shaft

speed ?

John

Yes that is true. It is chain driven with a reduction. What ever RPM oil
pump speed
is what we are interested in. Sorry not to be clear about that.

Paul Lamar

Well, you'd better believe it cavitates, and in a spectacular way!  BTW,
the reduction ratio between the e-shaft and the pump is 1.5:1, NOT 3:1.
Up to approximately 4,000 shaft RPM, the pump pushes a flow of oil
increasing linearly with RPM (16 gal/min at 4,000 RPM) while humming
gently.  Oil is also being squirted out of the pin hole on the back of
the pump body to lubricate the drive gear and chain.

Then, quite suddenly, the sound the pump makes changes and it starts
howling.  The flow of oil remains at 16 gal/min for a while and then
slightly goes down with increased RPM.  No oil is being squirted through
the pin hole anymore but, on the contrary, air is being sucked in,
turning the oil downstream of the pump into froth.

The experience is perfectly repeatable. If these are not symptoms of
cavitation, then I'd be very curious to know what it is.

But we have some good news:  We took a '93 13B dual-turbo model pump
(Mazda had modified the pump with a passageway to feed oil through the
rear rotor) and fed it from the side of the pump with a second pick-up
tube.  It worked beautifully:  NO noise anymore, no air being sucked in
either, and 20-21 gal/min of oil flow at 5,400 shaft RPM

Francois Badoux

I highly doubt this Francois. Hundreds of race cars have used this pump
for 30 years and they rarely get BELOW 6000 RPM. Many in 24 hour road
races. If what you say is true the rotor bearings would be failing long
before 10,000 or 11,000 RPM. The typical redline for a race engine. I
think you need to look elsewhere. Perhaps the viscosity
or type of oil you are using. Even that is rather unlikely. Try
some automobile oil and see if you can repeat these results. Send
me a picture of your test rig. Who is doing this test?

Paul Lamar

If the above by Francois is true, even if only with some oils, it would seem that a quick solution would be to close the chain lube hole on the back of the pump and supply oil to the chain and gear from a downstream source?  Feasible or not, I don't know.

Bob Lemings

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