Oil Pump Dyno

[WConley]

Some of you guys may remember the spin test machine I built about a decade (!) ago.  We learned a lot about valvetrain dynamics, specifically on the 427 SOHC.  The machine is powered by a 5 HP electric motor on a variable frequency drive.  It is capable of spinning the camshaft up to 5,500 rpm, corresponding to 11,000 crankshaft rpm.  Here are a couple of pictures from back then:





Here's a YouTube clip of the machine starting up at low speed:
https://youtu.be/-Slp184d0sY

This is a typical clip of a high speed valve event test I did with the stroboscope:
https://youtu.be/XCRrONYwBk0

We learned a lot, and broke lots of valvetrain parts.  Since then the machine has sat in a corner of my garage, unloved    Well, it's now back for a second life!  I've built a fixture that bolts onto the spin machine which lets me run automotive oil pumps.  I use a SOHC stub cam on cam bearings in a frame.  The pump mounts to a removable block and engages the cam drive gear, just as on an engine.  Oil is recirculated into a reservoir pan.  Here are some shots of the latest configuration:





The two pictures above are from early in the build.  I've added temperature, flow, and pressure measuring instruments, an adjustable valve to set flow restriction, and a dyno torque measuring system.  The machine has evolved a bit as I figured out what didn't work    Now it seems to behave pretty well!

Here's what it looks like now.  You can see the pressure gauges, and the big "FML 250" box is for the turbine flow meter.  I went through three other types of flow meters before I finally got this to work!



Here's the dyno torque arm on the motor, and the display:




I also added magnetically mounted splash shields to help keep the oil where it belongs:



Here's a Melling M-57 HV oil pump for the FE, mounted on the drive block and ready to test:



Obviously there are a TON of details that I won't bore you with, but I'm happy to answer questions.  This has been a big undertaking...

So what does this thing do?  I can test an oil pump at any flow restriction and temperature I want, with any type of oil.  For the first test, I got a blueprinted Melling M57-HV high volume pump from Precision Oil Pumps.  I used conventional 10W-30 oil and set the hot idle pressure at 30 psi, corresponding to a quality new engine build.  (Thanks, Brent Lykins for that recommendation!)  Oh - Temperature is 200 degrees F.  Believe it or not, just running the machine up for several minutes will put that much heat into the oil.

Here's what the flow and pressure look like.  There is a bit of internal pump leakage at low speed, which is why the curves jump up off - idle.  I re-ran several times to verify this.  Also, notice how the flow breaks down at high rpm!  This is due to the pump cavitating and aerating the oil:



(Note that I've also attached the chart so you can read it better...)

I was surprised by the cavitation at the top end.  Here's something even more surprising.  This is the clear outlet line from the pump under normal operation:



Here is the same outlet line after the pump has been bypassing / cavitating for several seconds.  Those are air bubbles in the oil:



I don't know about you, but I don't like the idea of something like that going into my bearings.  To be fair, this is after several seconds at 7,500 rpm.  It does take some time for this much air to get into the oil.  Still, the flow curve drops off right away which shows that cavitation has started.

Anyway, this is what I'm up to!  More to come    I just got a POP standard volume M-57 pump to run.  I'll be doing a comparison of the standard and high volume pumps under the same conditions.  Fire away with questions!

[GerryP]

What are the chances that you can run that output through an oil filter?  I know the filter will probably go into bypass through much of the circulation but I'm curios to see if the addition of a filter -even in bypass- helps to reduce that aeration.

[WConley]

Forgot to mention - The M-57 HV pump uses 2.92 HP at 7,500 rpm.  The parasitic torque is fairly linear, rising only slightly as rpm goes up.  It's a little over 2 ft-lb at the crank.

Note that this parasitic loss includes the crossed gears that drive the pump.  They're pretty inefficient, but that is how it's done in our FE's.

[WConley]

What are the chances that you can run that output through an oil filter?  I know the filter will probably go into bypass through much of the circulation but I'm curios to see if the addition of a filter -even in bypass- helps to reduce that aeration.

Yeah it's possible to route through a filter.  I don't think this will take the air out, because a lot of it is dissolved in the oil.  I've noticed that the oil has to sit still in the pan for several minutes for the air to work itself out the top.

[GerryP]

I was thinking a filter, again even in bypass, would act similarly to a dry sump tank.  I clearly don't know that, but just curious if it helps.  I can't imagine an engine lasting very long with a mix like that.  I know endurance applications use a dry sump not only for superior oil control, but also for the benefits of that big tank.

[MRadke]

I got my limited cavitation training in a class put on by Waterous fire pumps.  They had a working cutaway centrifugal pump where cavitation could be induced in different ways.  The most obvious was lack of supply for a given impeller speed.  The lessons that were driven home were that a pumps capacity changes drastically based on pump rpm, flow and pressure.  A single stage fire pump rated for 1500 gpm at 150psi can quickly become a 750 GPM fire pump at 250psi, or deliver a greater than rated volume at an unusable pressure.

Do you feel that the oil pump is cavitating due to lack of supply, or lack of capacity to keep up with flow when the pressure relief opens?

[blykins]

That is downright slick. 

[WConley]

Gerry -  I think it's the time sitting still in the dry sump tank is key to getting air out.  There would be so little time sitting in the filter that I don't think we'll see much of an effect.

MRadke - These oil pumps are positive displacement, unlike the centrifugal water pumps.  I would guess that when the bypass plunger is opening it creates a very low pressure region in the inlet.  This lets dissolved air come out as bubbles.  Maybe a pump guru can chime in here...

[GerryP]

Well, there's no denying that is an awesome rig!

[MRadke]

Gerry -  I think it's the time sitting still in the dry sump tank is key to getting air out.  There would be so little time sitting in the filter that I don't think we'll see much of an effect.

MRadke - These oil pumps are positive displacement, unlike the centrifugal water pumps.  I would guess that when the bypass plunger is opening it creates a very low pressure region in the inlet.  This lets dissolved air come out as bubbles.  Maybe a pump guru can chime in here...

I believe that your theory on the source of the bubbles is spot on.  I've actually witnessed it in action. 

I realize the difference in the style of the pumps, yet I can help wonder whether a pump designed for higher volume, geared down to run at a lower rpm, might take care of the cavitation issue.  The issue of pumping the pan dry could be addressed with restrictors on the pressurized side of the pump.

[mbrunson427]

Bill, can I send you an oil pump to test? There's a local company that I have always had modify our oil pumps and it would be awesome to know whether it's worthwhile!

[WConley]

I realize the difference in the style of the pumps, yet I can help wonder whether a pump designed for higher volume, geared down to run at a lower rpm, might take care of the cavitation issue.  The issue of pumping the pan dry could be addressed with restrictors on the pressurized side of the pump.

I'm doing some other work on that very question.  Still to early to publish, but evidence is pointing to the bypass recirculation feature when the pump reaches its design pressure limit.

[WConley]

Bill, can I send you an oil pump to test? There's a local company that I have always had modify our oil pumps and it would be awesome to know whether it's worthwhile!

Mike - I think we could arrange something, though I'm not looking to be in the business of testing pumps.  It's hard messy work!  Shoot me a PM and maybe we can figure out your needs.

[MRadke]

I realize the difference in the style of the pumps, yet I can help wonder whether a pump designed for higher volume, geared down to run at a lower rpm, might take care of the cavitation issue.  The issue of pumping the pan dry could be addressed with restrictors on the pressurized side of the pump.

I'm doing some other work on that very question.  Still to early to publish, but evidence is pointing to the bypass recirculation feature when the pump reaches its design pressure limit.

The problem that you will have is that if the pump is making turns for 150 psi, and you have it regulated to 80, the volume of oil vented will exceed the capacity of the intake plumbing.  If the pump could be designed to give the desired volume and pressure of oil at the maximum intended rev, and not need to be bypassed, cavitation could be avoided.  Of course it would still need to provide the minimal pressure needed at idle.

[WConley]

The problem that you will have is that if the pump is making turns for 150 psi, and you have it regulated to 80, the volume of oil vented will exceed the capacity of the intake plumbing.  If the pump could be designed to give the desired volume and pressure of oil at the maximum intended rev, and not need to be bypassed, cavitation could be avoided.  Of course it would still need to provide the minimal pressure needed at idle.

Exactly    This is the nature of the other work I am doing.  You hit the nail on the head.