oil pressure drop question

[Belgian1979]

I'm getting the impression you know what my engine is about since you bring up the Chevy 302 CAN AM (wasn't that one dry sumped ?). Anyway this is a short stroke/big bore combo that is made to run 7500 rpm, maybe even more.

That aside, is not the reason why I'm running the HV pump. I have an extensive oiling system as you can see from my first post. I've experienced first hand that getting everything filled required a lot of volume (especially the accusump). That aside I also run roller lifters with the pressurized bearings and valve spring oilers, so I do need extra volume.

I ran a new test today with the oil level lower than usual. This time the oil pressure stayed put. So it seems it was caused by windage, due to a to high level of oil. I got some wrong instructions from Canton as to the actual content of the pan. They said 7qrts at first, than 6 qrts. Today I ran a little under the 6 qrt mark and it seemed to have helped.

On the other hand, actual running pressure is 60 psi, so this is also the pressure that the accusump is at when I fill my tank. However since I have idle pressure at 40 psi hot, it seems the accusump equilizes to this pressure dumping some excess oil in the pan. It noticed that upon driving off from some extended idling that the oil pressure was fluctuating some, then when the accusump had filled again it was stable again. I might even need to drop the equivalent amount of oil to avoid this.

So far so good it seems.

 

[Belgian1979]

Actually it was oil frothing from the oil level being too high. Now I still need to strike a balance with the accusump.

 

[OVERKILL]

Originally Posted By: Belgian1979
I'm getting the impression you know what my engine is about since you bring up the Chevy 302 CAN AM (wasn't that one dry sumped ?). Anyway this is a short stroke/big bore combo that is made to run 7500 rpm, maybe even more.


I don't believe so, no. The Chevy 302 in the '69 Camaro had a somewhat traditional oiling system, though I'm not intimate with the details on that one unfortunately. However, given the engine's usage profile, I think it is a good reference point for somebody building a high RPM SBC, as that was that engine's purpose and they saw great success with it.
Quote:

That aside, is not the reason why I'm running the HV pump. I have an extensive oiling system as you can see from my first post. I've experienced first hand that getting everything filled required a lot of volume (especially the accusump). That aside I also run roller lifters with the pressurized bearings and valve spring oilers, so I do need extra volume.


Not that it is identical, but the SBF builds (and the very limited number of SBC builds) that I've been involved in have primarily all been roller. However, you've gone a bit above and beyond those with your spring oiler setup and I'm not sure as to the volume requirements of such a system. Most guys in SBF land do step up to an HV (SP) oil pump when running a supercharger that shares the engine oil. Though it has been debated as to whether this is really necessary or not.

I would be interested in seeing the behavior of your system with a stock volume 302 pump (which I believe was the same volume as the regular SBC pump, but higher pressure). Not that it is going to happen of course, but it interests me nonetheless as to what the behavior of this package would be like. I say this because depending on how much oil is going out the bypass, there may really be no difference.

Quote:
I ran a new test today with the oil level lower than usual. This time the oil pressure stayed put. So it seems it was caused by windage, due to a to high level of oil. I got some wrong instructions from Canton as to the actual content of the pan. They said 7qrts at first, than 6 qrts. Today I ran a little under the 6 qrt mark and it seemed to have helped.


That's fantastic news and does indeed sound like it is pointing to windage. Please keep us updated on this.

Quote:
On the other hand, actual running pressure is 60 psi, so this is also the pressure that the accusump is at when I fill my tank. However since I have idle pressure at 40 psi hot, it seems the accusump equilizes to this pressure dumping some excess oil in the pan. It noticed that upon driving off from some extended idling that the oil pressure was fluctuating some, then when the accusump had filled again it was stable again. I might even need to drop the equivalent amount of oil to avoid this.

So far so good it seems.


Interesting. I've no experience with the accusump. With your pan setup it almost sounds like overkill........

 

[Belgian1979]

Yes, the accusump can be considered to be overkill, but I added it for Insurance. I think during this oil pressure issue it has been of good use to me, preventing possible engine failure already. So, I'm still glad I have it, although I need to still strike a balance in oil levels.

As for bypassing, yes. I think all pumps are bypassing oil. In essence you need overcapacity in order not to starve the engine. There is more however. If the pump creates vacuum when pulling oil out of the pan, you have a potential cavitation risk. The bypass in these pumps exit to the inlet side, so in essence they supercharge the inlet side (put it on higher pressure) Its the same as using a booster pump to prevent cavitation. So actually the bypassing is not such a bad thing after all.

To note is that not all roller lifters are equal. Some have oiling to the roller some do not. If you do have oling to the roller you've added 16 extra leakage points.

After all things are done and looking at what I found out, my thinking is that with a higher volume pump and some more leakage points in my engine the pump certainly has its place. It will surely bypass more oil, and although heating it up a little more (which is why I have the oil cooler) will actually help it reduce cavitation since it will put the inlet pressure at a higher point.

I'm no engineer though, so I could be wrong.

 

[OVERKILL]

Actually, most stock-style pumps aren't bypassing unless the oil is cold and thick, or you are romping on it. The bypass on the Ford 302 is ~65psi IIRC and even with 0w-40 in the sump, when the oil was good and hot, it would only get up in that range when you were wound right out.

The bypass is simply there to deal with excess volume that can't be forced through the engine at a given head pressure, that is, the pressure at which the relief starts to open and operates the bypass.

In many HV pump situations, there is so much extra volume that it cannot be bypassed and so it artificially elevates oil pressure as a byproduct. This is how you can have an HV/SP SBC pump running at 70PSI when the bypass is 55psi. There's no advantage to this scenario, as you are just thrashing/heating the oil unnecessarily.

The goal with a setup like yours that is far from stock is to find the right balance between the required volume of the system in order to keep everything lubricated and the point at which you are just moving the oil around in the pump because it can't go through the engine. This is often why high performance (stock) engines simply have elevated bypass pressure whilst retaining the stock volume. This is sort of a tangent of the 10psi/1000RPM rule. If you are spinning it to 7,500RPM, you probably want a bypass setting north of 70PSI. Now of course that's a guideline really, but in application, it does seem to be somewhat adhered to.

With respect to lifters, I can only assume you are speaking specifically of the solid roller variant, which is quite right. There are a couple of different types with different oiling (or the lack thereof) setups. My builds have all been hydraulic roller, so the leakage is most certainly present in all of them. I think you may be over-thinking this part, as the roller SBC's and the hydraulic flat tappet SBC's, which all leveraged a stock volume oil pump, would have had more lifter leakage than your solid roller setup IIRC.

The one exception with your engine seems to be the spring oilers. As I said earlier, I'm not familiar with the volume requirements of this system, and it is most certainly another leakage point that isn't factored into the stock oil system design. So this may in fact potentially warrant additional volume.... But we don't really know for sure.

Anyway, keep me posted! It sounds like a great setup

 

[Belgian1979]

Well the story continues. I was chasing the reason why the accusump was dumping oil into the pan at higher oil pressures. I thought I had the epc valve with the 25/30 rating, but after a lot of discussion I seem to have the 55/60 one. Since I ordered the part a long time ago, I do not know if it was my choice or not, so I'll have to assume it is.

Anyway, with regards to the oil pump bypassing, I'm going to add this : I witnessed a test on a positive displacement pump in an oil reworking facility for my job. It was a very big pump and the setup of that pump is similar to what is used on a SBC pump, in the sense that the bypass opens at 5 bar towards the inlet side. This unit had both pressure gauges on the inlet as on the outlet side. We were closing a valve as to test the vibrations under certain conditions and evaluating readings among which the pressure on the inlet side. Usually they were around 0,1 to 0,3 bar. When the bypass valve opens you can see that the pressure actually goes up. I talked to the engineer that was doing the tests and he explained to me this was done to help reducing cavitation. Now the motor on that pump had a frequenty regulated input so it's power output could be regulated something which you don't have on an oil pump on a motor. But an oil pump, certainly at elevated rpms will Always bypass oil. The bypassing itself only has one drawback and that is that it will heat up the oil some. In essence to avoid cavitation, which is a lot worse than to have oil bypassing, bypassing more is not so bad. Like I said previously it functions as a booster pump.

 

[Shannow]

Sometimes the simple things can get missed

Maybe ???

Quote:
Also, I've noticed that oil pump driveshaft engagement has become an increasing problem. With everybody making trick-of-the-week intakes and different distributors, I've noticed some cars having trouble because the oil pump shaft isn't getting the engagement it needs. During mock-up, I will have the intake on the engine and bolt on the distributor. Then, I flip the engine over and check for total engagement of the oil pump driveshaft. Be sure to have some end play. The common complaint when this is a problem is, "It has 60 psi of pressure, then when the engine gets up in the rpm, the oil light comes on." Look at the ends of the shaft. It will be shiny from riding up on the end and not turning the oil pump--bad news!

Read more: http://www.circletrack.com/tipstricks/139_0306_engine_oiling_tips/#ixzz2jvD8BndJ