Originally Posted By: Linctex
Originally Posted By: ZeeOSix
There are a couple of threads in this forum talking about the oil pump specs on Subaru 4-cylinder turbos, and the factory shop manual showing the pumps in those engines putting out something like 12~14 GPM. I'm sure that there are many factory stock high performance V8s on the road that put out way more than 5 GPM. My Z06 was rated at around 10~12 GPM max output. Something like a 4 banger Honda Civic will probably be putting out 5 or 6 GPM max.
It's been a few years since I have built racing engines, But I recall those numbers were always "bench test" numbers... and at "zero restriction" at that. I seem to remember all published Melling pump info was like that.
Meaning, stick the pump in a 5 gallon bucket of oil and spin it with a drill while it pumps through a 1/2" hose (at 0 psi, really) into another 5 gallon bucket. They'll move Many ,many GPM in this scenario, yes.
However, your "typical" engine, with typical tight bearing clearances (forget drag engines for a moment) - will NOT flow that much, no matter what the pump specs are. Like I said - - you physically can NOT drain and fill a 4-5 quart oil pan every 3-5 (20 & 12 GPM, respectively) seconds.
Keep in mind that when the pump is on an engine it can supply oil at 100+ PSI (whatever the pump releif is set to - some Subarus engines are around 140 PSI relief) in order to force it's positive displacement volume through the engine's oiling system. Also keep in mind that the total oil flow going through the engine isn't all flow to the main and rod bearings. Also, main and rod bearing oil flow volume is a function of both RPM and oil supply pressure, so that's why they can flow way more than you would think just due to pressure on a tight clearance.
All the oil that leaves the oil pump goes through the full flow oil filter. So in other words, the oil filter is seeing all the flow that supplies the engine's oiling system if the pump is not in pressure relief. Most high performance engines have larger oil sumps (6 to 8 quarts) to help keep the sump level at a reasonable level when the engine is at high RPM and the pump is putting out max flow.
If the oil pump is not in pressure relief, then all the volume leaving the pump is going through the filter and engine. Engines certainly can flow 10~12 GPM with hot thin oil. My Z06 was not in pressure relief at near redline, so the filter & engine was seeing all the flow. It wasn't a few GPM, but more like 7 GPM if you believe the Melling graph.
And bench testing oil pumps with no back pressure is very misleading data, as it won't show what the pump's internal slippage is. I suspect those Melling graphs are with some significant back pressure, and probably flow that was recorded on an actual LS engine. That why they knee over in the high RPM region.
Originally Posted By: Linctex
Oil simply will not flow by gravity into the pan fast enough to replenish the supply. I also know for a fact your crank doesn't move a gallon of oil every 3-5 seconds - the windage losses would be insurmountable. No one builds a windage tray or dry sump system (single stage) capable of evacuating an honest gallon of oil every 3 seconds. It just isn't realistic to expect an oil filter must flow 20 GPM... because your engine simply doesn't.
It certain can when it's hot and thin as water. And if the pump has a high pressure relief setting, it ensures that all the oil leaving the pump goes through the filter and engine. I like this old 1937 demo:
https://youtu.be/vz2p1SvuYjY?t=9m45s
