Drysump pressure drop 2

[blamkin]

Morning folks, first post. I've spent a couple hours digging around and didn't see my question answered before so I thought I'd post a new thread.

I am racing an EProduction mazda miata in SCCA club racing. As the stock miata oil pump regulator is proned to problems, I've "made the plunge" and switched over to drysump.

On startup, I have adequate pressure - about 40psi at 2K rpm idle. As RPM increases, so does oil pressure- up to 75 or so when the regulator kicks in.

Here's my issue: After startup, letting the car idle for say, 60-120 seconds, the pressure starts dropping... down to say 15psi where I get chicken and shut it off. The oil temp is maybe 100-110 at that point - way before anything is warm.

If I let the car sit for 30 minutes, and try again- voila my oil pressure is back to 40 ... but then the dreaded pressure drop starts all over again.

My system is the following: four-stage TDC pump, two -10 scavenge lines from the pan, one -10 scavenge line from the back of the head (in the valley with the valve train). The pump section for the head scavenging is much smaller than the two pan scavenge sections. Each of those lines is about 18" in length.

There's a -12 line heading back from the engine compartment to the trunk area; that line enters the top of the 24x6 tank. Another -12 line returns along side that line back to the pump.

The pump outputs into a -10 line, into a filter, into a cooler, and into the block at the stock oil filter input location. Just above that input is the stock pressure sender location, where I have my current gauge attached.

After speaking with several people, I believe one of several problems are possible - but I am looking for input / thoughts / whatever learning I can get.

1) The tank lines are too long, too far away from the pump, or simply the tank is too low relative to the pump for it to suck oil from the tank.

2) The head scavenge line is never below the oil level in the head. Specifically, it's basically in free air as far as I can tell. This seems like it's just sucking air into the system (minimal oil) and is asking more as a vacuum pump. Unfortunately for me another several cars have this setup but do not have my problem.

3) Some other problem I haven't thought of.

Diagnostics I've done so far:

1) Removed the line going to the tank, and verified that the pump is sending oil down the correct line. Simply turning the pump at starter speed shows the lines are hooked up correctly...

2)... however when the car is running, there really isn't that much fluid coming out. Yes with 20 seconds of cranking I can fill a 1-qt bottle, but the stream doesn't seem that consistent to me anyway.

3) When the pressure has dropped, I removed the valve cover and ran the starter again. You can clearly see a few air bubbles coming out the oil galleys for the lifters. It's not foam by any stretch, but there are bubbles for certain.

Any and all direction is appreciated. Thanks for your time.

 

[Racer704]

Yes you could add a scavange line to the head but since we add it to the valley area more for help with vacum and its sucking ait and oil....the biggest problem is the vacum created with the vacum pumps also at idle..this scavange line is -10...i have no issues...I was giving all things to look at as i have been there done thst and have 100' of feet of line to prove it and alot of hours of work finding it.....

Pat if you have a suction to the top side of the of the area of return and it gets coverd with oil that said vacum will hold the oil from returning to the pan properly and the pump will over fill the top side of a the motor...

Having vents that stand up above any pooling of oil will help along with adding returns...Also I alwayas start and warm the engine with are vacum pump line lossend from the valve cover...I have also moved it to the liffer galley but this pump is a monster...it will pull 25 inches on a 750 inch nitrous motor going down track...I try to okeep the pump regualted at 15 to 18 as even with added piston squirters and coted wrist pins the little HP made from added vacum isnt worth on a nitrous motor....I also use the vacum reading from the pass to help tell me the seal of the engine from rings to gaskets....

 

[Racer704]

One more thing to add here thats been stated, I run an all aluminum motor with a billet block and main caps...in one minute and this is with heated and primed oil to 100 to 120 degrees are clerances X2 in the mains...

As long as i have 15 to 20 at idle and it has 70 going thru the lights i am fine...as long as there are no drops and spikes durring the run....pressure robds power and 10lbs per 1000 XRPm is fine....volume is whats needed more then pressure....I run alotg of oil to the top side of are motors because of the valve springs pressure of 400 to 425 at closed and well over 1200 open so are push rod cups and rockers needs as well as springs oil...I run a 9/16 taperd exhust push rod and if i could it would be 5/8....anyway going off track here of the original post sorry...

 

[patprimmer]

Racer.

This guy is running a Mazda inline 4.

It has no valley.

It has big oil returns.

It is DOHC so the need for lots of oil overhead is not there.

Two suction points in the sump will draw more volume than the one in the top, admittedly most of the oil will also be in the bottom and using that capacity to a greater extent.

I see no problem with that aspect. It is much more likely the positioning of fittings or the routing of lines so they bend and collapse under suction, or the air is still trapped in the oil as it enters the pressure pump pick up.

If it is air it is likely tank size/design at fault.


Regards
Pat
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[Racer704]

Pat I would agree,the suction and collapse of lines is something always over looked and the lack of adding the spiral core as its a pain is the butt.....tank design is something since he did say it was a old system he used at the start so it could be a poor tank also......

I guess we will se what happens when he finishes his lines....

Sorry for being stuck in the large V-8 world but the suction side is something I use to over look years ago and learned the hard way....even high end engine builders dont add the spiral core...learned that from Johnsons pumps...smart man....

 

[thruthefence]

Did you fabricate your own oil lines, or did you farm them out? If you did, (and I mean no disrespect here) did you use the proper assembly tools? With the mandril that enters the hose liner, as the fitting is assembled onto the hose?
(I'm assuming 'real' aeroquip style hoses.)

I have seen hoses that when screwing the fitting onto the hose,(without the mandril) the fitting cuts the liner, and raises a sliver of it up inside the hose, obstructing it.

In service, especially in a scavenge situation, the flow can get up between the liner layers, causing it to bulge out, cutting flow even more.

In the days of my youth, I was called upon to evaluate high oil consumption on a turbocharged aircraft. It was determined the oil was departing through the turbo exhaust. An expensive turbocharge change was accomplished. No help. The scavenge hose was inspected, by blowing air through it, which showed ok, but one of the old moss-backs suggested removing the fitting & inspecting the hose itself, which had indeed suffered a lining separation.

 

[evelrod]

Just a little I thought I might add...

I've been using braided SS hoses and AN fittings for many years. I've assembled them with the "proper" tool and "by hand" in the field when necessary. All I can say is that if you use skill and caution, barring a few punctures and loss of blood, proper connections are possible. Always double ck the job, either way it's done.

Collapsing AN -012 scavenge line? "You betcha"! (sorry, I couldn't help myself...too much cable news). On our current scavenge lines we use a 3/4" industrial item specifically designed for high temp suction/vacuum use in the oil industry. We had them made up by the local "Hose Man". A better option for the purpose, albeit not cheap.

Rod

 

[blamkin]

Folks, my problem appears to be solved.

After running 15 minutes, at 180* oil temp, I have 42psi of oil pressure at idle (about 2K).

Thanks John at AVIAID for supplying a great pump and being so helpful.

I guess I won't really know whether the pump was the fix, or if one of the other two changes I made was the real fix... I guess no one knows for certain.

If I run into any issues at miller this weekend, I'll consider adding the springs - if anyone has a suggestion as to where to buy such a thing I'm all ears.

...and thanks to everyone for their suggestions and patience.