John,
You've touched on a number of key points here and you'll likely come up with a lot of different opinions.. Here you'll have mine..
I'd like to hear comments/opinions about an engine's "real" oil flow and pressure requirements? Some builders reckon a 30 GPM dry sump pump is bypassing around 2/3 of its flow at high RPM and pressure.
True about the bypassing... If you've ever watched the flow-rate on the bypass of the pump at Max HP, you'd be convinced..
Too, the old rule of thumb of 10psi per 1000 RPM isn't holding anymore. Apparently some NASCAR teams are running as low as 50psi to gain a few ponies.
Engine builders of "the day" like my old hero Smokey Yunick, used this as a rule of thumb given the quality and abilities of the oil, the bearings and materials..
So, are we over oiling our motors?
In a word. Yes.
Understandably, we want to have more oil pump capacity than the motor needs, just as we do with fuel pump capacity, but any oil that goes over the pump's relief (bypass) valve can be considered wasted horsepower.
B-I-N-G-O - you mentioned the magic words... Oil Pump Capacity. That capacity is measured in pressure.
We seem to, somehow, get carried away in the capacity department though... That excess capacity costs us in HP, Weight, Expense..
On some of the most powerful and championship winning engines and cars that I've worked on, they have oiling systems that are designed to carry "enough" capacity to bring things under control should there be a problem, but not enough to drive from here to China... Case in point was about 10 years ago we just finished dyno testing a new small block Chevrolet engine that carried a displacement of 435 Cubic Inches and produced 820 HP on 110 octane racing fuel fed through a single 4 barrel Holley carb. It had a Weaver dry sump system that carried 5 to 7 PSI at an idle and 35 PSI at 8,000 RPM on 10w30 Synthetic oil. It was refreshed after ~500 miles and the bottom end was *perfect*. BTW - it won ~100k in races..
So when a 30GPM dry sump pump is bypassing 2/3 of its output, I wonder how much HP is actually being wasted?
I don't think there is any one right answer, but we've picked up ~10% when we dialed down the pressure and disabled a stage in the pump.
How much oil flow does the motor really need?
I think a lot has to do with the comfort level your engine builder has with running closer to that "edge" in Pressure (capacity) and flow (carries away heat) in order to protect the bearings.. Remember that the dyno is a controlled environment. Controlled temperature and humidity. Very easy to build an engine that never leaves the dyno. So engine builders need to also be thinking about the environment, the g-forces, the part throttle loading, the numerous starts when the engine might be a little cold.. etc....
FWIW - I was at the store a couple of weeks ago picking up a fresh 6-pack of oil for my daily driver. 0w20 Mobil-1.. Another guy was picking up 6-packs of it.. Since it's a rather new blend on the market I asked him if he was just stocking up - he replied that this was just one oil change some spares.. I smiled and he said "Drysump"... They were dyno testing and had just finished with 5w20 and now heading for 0w20. They picked up another 30hp in dropping from 10w30 to 5w20 on a 600hp engine. No idea - yet - what they picked up or left on the table with the 0w20. I gave him my number..
It'll be interesting what they found..
BTW - We don't float bearings on oil by pressure but by the molecular structure of the oil itself....