Engine Oil Flow Requirement

[JohnC]

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.

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.

So, are we over oiling our motors?

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.

So when a 30GPM dry sump pump is bypassing 2/3 of its output, I wonder how much HP is actually being wasted?

How much oil flow does the motor really need?

 

[Ron Earp]

Enough to float everything.

All the race cars we race, including the ones for 13 hours at a time, run about 45-60 psi with RPMs that range from 5k to 7.5k. When rebuilt it isn't due to bearing wear, but the head needs freshening.

Ron

R

 

[Randy V]

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....

 

[Jac Mac]

1. Why do virtually all the pump manufacturers 'squirt' the bypass oil back into the pickup side of the pump- cant do much for the oil column to have a hi/pressure hose aimed at it on the way to the pump gears.
2. Most motors 'require' about the same pressure ---''' measured at the centerline of the main bearing's '''--- its only the restictions/corners of the oil galleries in the block & their layout that dictates what pressure a gauge in the factory location needs to read in order to supply the correct amount--remembering of course that one or more bearings will get less than others.

 

[Dave Bilyk]

Guys,
I find it difficult to believe that a pump with the flow and pressure suggested will use significant hp.
Physics suggests 30USgal/min x 50psi = 0.875 hp hydraulic power.
gear/rotor pumps would be fairly efficient, and even accounting for windage and losses in the input drive gear or pulley, my guess is the total will be no more than 2hp IMHO.
Anybody have any real data here?

Edit; If there are significant changes in engine output such as Randy's case, could it be that excess oil in the sump is being churned by the crank?

regards
Dave

 

[Keith]

Are we not also talking about putting uncessary "heat" into the oil with a higher pressure than needed, pump? Keeping the oil cool enough to do it's job is a difficult enough task in many performance applications, without adding to the problem unecessarily..

Or am I talking 'hot air?' :laugh:

 

[Russ Noble]

1. Why do virtually all the pump manufacturers 'squirt' the bypass oil back into the pickup side of the pump- cant do much for the oil column to have a hi/pressure hose aimed at it on the way to the pump gears.

That also struck me as bad practice, so I have chosen to return my relief oil to the tank, and in the case of the trans (no tank) dump it directly back through the sideplate. In both cases it has already been through the cooler/heat exchanger, so that should keep everything at a better temperature too.

FWIW I am using one stage of my drysump pump to move the trans oil. When I was testing my spraybar a brand new 4hp electric motor was really struggling to turn the pump at about half revs. I didn't have a pressure guage hooked up to the system but I would guess it was generating about 50psi. I then doubled the size of the squirter holes but never rechecked.

See photos in post #155 of my build log http://www.gt40s.com/forum/gt40-build-logs/16138-kiwi-scratchbuilt.html

 

[Jack Houpe]

Are we not also talking about putting uncessary "heat" into the oil with a higher pressure than needed, pump? Keeping the oil cool enough to do it's job is a difficult enough task in many performance applications, without adding to the problem unecessarily..

Or am I talking 'hot air?' :laugh:

Valid question! Does it? I have my doubts about the high pressure high volume pump not doing more damage than good my self.

 

[Jac Mac]

Valid question! Does it? I have my doubts about the high pressure high volume pump not doing more damage than good my self.

Spot on!!! It exagerates every 'problem' that the oil system can suffer from.
1. If you get into a situation where the pickup is uncovered it pumps 'more' air into the system which then takes longer to replenish.
2. The 'shock' loads of no pressure/lots of pressure during these periods put large loads on the pump drive shaft & gears.
3. On cold start with cold oil the 'system' simply cannot flow what the larger pump can supply even with the relief fully open at these times- Ive seen well over 100psi on oil gauges with guys that jazz the throttle- then they wonder why the dist gear & drive call it quits!
4. A system where a relief valve is in operation all the time will have aerated oil in it,plus the continous recirculation of the bypass oil within the pump creats unecessary heat. The pressure will then reduce the size of the aerated oil bubbles until the pressure drops which in the case of the bearings is somewhere on the rod bearing inserts surface -- thats the last place you need an oil film breakdown & why you usually see a spun brg as the first indication--- after your 'hero' driver has done a couple of extra laps to see if the 'problem' will fix itself.