oil pressure 1

[golfpin]

how much oil pressure is sufficient, Chevy small block std oil system supposed to be good for 600 bhp does this mean more bhp more Oil press required or is it a function of bearing area related to revs therefore bigger inertia loads?
I was lead to believe that when running the VW water cooled 8 valve in Germany in one of he single seater categories that the oil pressure was reduced to 15 lbs/sq inch, less bhp drag from oil pump don,t know how valid this statement was source was pretty good. Does any one know what the oil press is in current F1 engines.

 

[MikeHalloran]

The oil pressure to support the bearing loads comes from something called "hydrodynamic lubrication". Google that. It's much, much higher than the oil pump pressure, and not directly related. Basically, if your oil pressure falls off at high rpm, you need a bigger pump, or less bearing clearance. What's really important is the oil pump volume; the pressure gage gives you a simple way to monitor that the volume is sufficient.

Reducing the pump pressure by fooling with the relief valve may not save much energy. Reducing pump pressure by using a smaller pump is a valid way to save energy, but you get to replace the bearings when you've gone too far, so it's a potentially expensive risk. The benefit is probably noticeable on a Vdub, not so much on a SBC.

I wouldn't want to go below the stock flow, because a secondary (maybe primary) function of the oil flow is to carry friction heat away from the bearings, and if you're messing with oil pumps, it's probably because you're increasing the power level and the friction heat.






Mike Halloran
Pembroke Pines, FL, USA

 

[romke]

oil pressure is not really that important. what is important is sufficient oil flow - which can be generated by a high volume pump at relatively low pressure. there is no relation of the oil pump pressure and the pressure in a bearing - which may actually be a few hundred times higher then in the feed line.

oil pressure gauges were introduced to watch the oil flow, because a pressure gauge was/is a much simpler device then a reliable flow gauge.

you may notice that oil pressure as shown by the pressure gauge will vary quite a bit with engine oil viscosity, oil temperature and engine speed. basically if you get sufficient oil flow to all the parts that need lubrication things will be ok. because less viscous oils flow easier they may have a favorable effect on cooling of bearings and on fuel consumption.

 

[TheBlacksmith]

Every so often, someone comes along and proposes reducing oil pressure to free up horsepower. From an engineering standpoint, since most oil pumps are positive displacement, this makes sense. However, the oil pump is a very small proportion of the parasitic drag, so reducing its power consumption by 50% may barely be seen and while the lubrication function is somewhat independent from oil supply pressure, you can compromise the cooling and cleaning aspects of oil. If you're after more horsepower, bigger gains can be had with an electric cooling fan that only runs when needed over a mechanical fan running all the time.

 

[Tmoose]

In the 1966 SAE paper 660342 "Chrysler Corportion's New Hemi Head High Performance engines" they spend over a page talking about the oil pump and lube system. "Work even prior to the hemi disclosed that a very considerable increase in pump capacity could be obtained by lowering the restriction on the suction side of the pump. This was accomplished by using a larger than standard pump suction pipe located in the normal location and adding a second pipe." ..... "This suction pipe was increased from 0.50 to 0.64 ID and the drilled holes (hole drilled in the block between the suction pipe and pump inlet) were increased from 0.547 to 0.688 which resulted in a 63% pump capacity increase."

On the face of that info all I can presume the gerotor pump was tearing the oil apart and cavitating badly.

 

[HPost]

Understanding that, in terms of engine lubrication, it is the resistance to flow that creates dynamic pressure.

It is flow x pressure that consumes power

Power consumed is a function of the overall efficiency of the pump.

Poor engine design can result in high pressure at the pump outlet and low pressure at the end of the gallery. This will just burn money.

The focus on fuel economy means that parasitic loses are not tolerated and a FE saving of just 1% is worth having.

Lowering the PV valves of bearings will allow for reduction of pressure, which will consume less power. Flow is becoming more important as it helps to remove heat from the pistons and bearings and as long the pressure is reduced in proportion, there are no FE penalties.

In reference to the pressure gauges. Most customers are ignorant of fluid dynamics and don't understand the relationship between heat and pressure. They got too concerned when the gauge didn't go "up" as high in the summer as it did in the winter. There were too many instances of false warranty issues relating to oil pumps. The solution, remove the gauge, fit a sensor and a bulb and just retard the engine and switch the "fault" light on in the event of a oil system event.

Never tell the customers what they don't need to know.

HPost
BEng (Hons) CEng MIMechE
Engine Design

 

[tbuelna]

The points made above regarding the importance of oil mass flow to specific components in the engine are excellent. The cooling provided by engine oil is just as critical as the lubrication it provides. With heat transfer from bearings/journals to the lube oil, it's the oil mass flow that matters rather than simply the oil circuit pressure.

The comments about the insignificant impact of oil pump drive losses are partially correct. For example, with a typical positive displacement engine oil pressure pump flowing 25gpm, lowering the discharge pressure from 80psig to 40psig would reduce the power consumed by the pump by less than 1hp. For a 500hp race engine that operates most of the time at WOT, this 1hp difference is not really significant. But for a small displacement production auto engine that operates much of the time at part throttle conditions while producing something like 20hp, that same 1hp difference could impact fuel economy by several percent. A 3 or 4 percent impact on the highway fuel economy of current production autos would be of great concern.

One issue with the typical positive displacement oil pumps used on engines is that they produce a fixed output volume per revolution and are driven at a fixed ratio of crank rpm. Since they must be sized to provide adequate oil flow at low rpm, their output at higher rpm is excessive. In order to prevent oil circuit pressures high enough to cause damage to filters, cooler cores, etc. the excess oil flow at high rpm is bypassed, which results in power losses. To address this problem many auto OEMs have begun using variable volume pump designs.

 

[Compositepro]

Tbuelna, thanks for the picture. That's a fascinatingly clever pump design, which I had not seen before. 25 gpm oil flow in a car engine seems really high. Is that a realistic number?

 

[golfpin]

Gentlemen thank you so much for all the interest and replies,
I am no more than a mechanic but it is I suppose the same could be said for Henry Royce. At this point I would like to throw a very curved ball across the plate. This is from personal experience, Merlees K8 8 Major a straight 8 cylinder generator engine with a 9 inch big end bearing width and big end journal diameter of about 12 inches, rev limit of 600 rpm ran with a an oil pressure of 75 psi. BHP I don,t know but it was a very large electric generator plant for mine in Mesapotamia.
Ruston Hornby tractor engine bore + - 5inch stroke about 7 inch runs with 25 psi bearing in mind [pun] that this motor was designed in about 193??? and runs on pre dinosaur oil my question is is there a relationship to bearing area, revs, and therefore inertia loadings. Another thought for those of us who are old enough 1948, [Chev comes to mind] and earlier cars the big ends were splash fed!!
Ronnie Harker in his book "The Engines were Rolls Royce" page 91 relates an experiment that was tried on the Roll Royce Merlin aircraft engine of 1943, they had been experiencing bearing problems and it was thought that it may have been as a result of the merlin engine cutting out under negative g. conditions [a well documented issue] Harker then went out and tested this by rolling the aircraft 156 times when the oil pressure would drop to zero, engine revs being 3600 this is about a 33000 cc engine, inertia loads? This test was followed by vertical dives with reduced oil in the tank which resulted in fluctuating oil pressure and using full throttle and boost, bhp probably in the region of 2000 [my guestimate depending on altitude] engine was stripped and found to be in "very good condition" quote.
comments?

with thanks golfpin

 

[MikeHalloran]

In 1978 I watched the pits during practice for a hydroplane race. One of the big name drivers would jump in the boat, fire the engine, go a couple hundred yards, then turn around and come back, yelling about no oil pressure.
... maybe six or eight times in a row.

I probably should have said something, but the whole crew was jacked up on adrenaline and didn't appear receptive to suggestions from the audience. They certainly were not receptive to suggestions from each other.

The engine, I forget if it was R-R or Allison, was equipped with a dry sump system, connected to a separator/reservoir tank by two long black hoses.
... of exactly the same size.

Clearly the hoses were crossed, so the engine was sucking oil from the top of the tank, until the boat got underway, then it was sucking air, etc.
I think they got it sorted out much later; the boat raced that weekend without a reported engine failure.


Which provides yet another data point to show that the _presence_ of lube oil at the point where the bearings inhale it is much more important than the pressure at the pump discharge. That's why splash lube works.

Here's a page that explains it in plain language:

http://www.marinediesels.info/2_stroke_engine_parts/Other_info/hydrodynamic_lubrication.htm

But Reynolds really just put the math behind it; someone else discovered the phenomenon that Reynolds explained:

http://www.marinediesels.info/2_stroke_engine_parts/Other_info/hydrodynamic_lubrication.htm

Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

.....25 gpm oil flow in a car engine seems really high. Is that a realistic number?

That 25gpm number was just for discussion purposes. As others noted above, engine oil flow is mostly based on cooling requirements. A rough estimate of the cooling provided by a 25gpm oil flow would be around 83hp, assuming a temp rise of 30degF, an oil density of 7.2 lbs/gal, and an oil specific heat of 0.65 Btu/lb-degF. 83hp (62kW) is definitely a lot of oil cooling capacity for most auto engines, but maybe not so for a 700hp race engine operating at WOT.

 

[bcs5274]

rule of thumb i was always told was 2 psi per 100 rpm

 

[pontiacjack]

"Rule of thumb" for typical automotive V8 engines is 10 PSI per 1,000 RPM.

 

[golfpin]

To all who took the trouble to reply my thanks, but would anybody care to comment on the Roll Royce story, surely someone out there has experience on the packard merlin.
Golfpin

 

[RossABQ]

What always strikes me in these conversations is that everyone recognizes the role of heat removal, yet comparatively few engines have oil coolers. Where is that heat being rejected? Radiative losses from the oil pan? (images of grimy, mud-covered oil pans come to mind) Contact with water-cooled surfaces in the engine? (not really "cool" surfaces, especially in the heads) It certainly seems adequate heat is going somewhere, based on the lack of problems.

 

[berkshire]

Ross,
Volvo recognized this problem in the 1960s, and fitted an oil cooler to their B18 series engines, this device was cooled by the coolant flow to the block, and also warmed the oil on a cold engine when the thermostat was closed.
The device turned out to be more trouble than it was worth, and was removed from later engines.
B.E.

You are judged not by what you know, but by what you can do.

 

[golfpin]

THANKS AGAIN TO ALL WHO WHO REPLY . MY QUESTION RE OIL/PRESS WAS PROBABLY SPARKED BY ANOTHER QUESTION WHICH INVOLVES 3 DIFF ENGINES OVER A PERIOD OF PERHAPS 20 YEARS ALL SUFFERED THE SAME DEMISE.

ENGINE1 1963 FORD 4 CYLINDER SET UP FOR LONG DISTANCE RACING NEW RODS SUITABLY MODIFIED [LIGHTENED BIGGER BOLTS ETC] AS WE THOUGHT WAS BEST O/P INCREASED OVER STD BY ABOUT 15 LBS FOR RUNNING PRESS OF ABOUT 60 LBS. CAR RAN WELL FOR ABOUT 4 HOURS CAME IN WITH A MISFIRE STRIPPED ENG AND FOUND NO 4 CON ROD HAD SNAPPED AT THE JUNCTURE OF THE CONROD BEAM AND BIGEND EYE. NO SIGN OF SIEZURE LOSS/LACK OF OIL IN FACT IF ANOTHER ROD HAD BEEN AT HAND COULD HAVE ASSEMBLED AND GONE ON RUNNING.

ENG 2 1974 FORD LOTUS CORTINA IN A SPORTS CAR, BUILT TO FULL RACE SPEC DRY SUMP ETC BRAND NEW VEGANTUNE RODS RUNNING IN AT ABOUT 6k BANG GUESS .. EXACTLY THE SAME AS THE PREVIOUS ENGINE CONROD SNAPPED AT SAME PLACE. NO SIGN OF SIEZURE OIL LOSS OVERHEATING.
FOR THE USA TEAM OUT THERE VEGANTUNE AT THE TIME WAS THE EQUIVALENT TO COSWORTH [IN TERMS OF PARTS] OR PERHAPS CARRIILO OF USA ... GOOD STUFF.

ENGINE 4 1998 350 SBC STEEL EAGLE RODS STEEL CRANK DRY SUMP ALL THE RIGHT GOODIES CONROD SNAPPED SAME PLACE; SAME, NO SYMPTOMS!
ANY THOUGHTS?
WITH THANKS TO ALL OUT THERE AND IN ANTICIPATION. GOLFPIN

 

[MikeHalloran]

Conrods live a hard life.
Racing makes it harder.
The failures you have described do not correlate to oil pressure problems IMHO.


Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

Usually rods breaking are from fatigue cracks initiating then progressing as the results of many 1000s of stress cycles (which don't take that many minutes at 7000 rpm). Are any of the surviving rods around, so you can have them mag particle inspected to see what might have been going on with them?

A rod breaking after 4 hours, or during run in?
I think the fellow doing your rod prep should stop numbering the rods by hack sawing notches in the I-beam. Or skip the high temperature HCl steam heat treatment prior to chrome plating.
Or maybe the crack(s) originated from one of the lightening holes he drilled in the beam web.

http://thumbs3.ebaystatic.com/d/l225/m/mH5-m8SUjC8dxL2qQpZNN7Q.jpg

Seriously, mag particle inspection of new and used parts can detect even small "indications" just waiting to grow to destruction.

 

[JayMaechtlen]

Ross
Some recent VW engines have water-oil heat exchangers.
For most engines, the oil splashed against inner surfaces of engine (and running down from head) exchange heat to the inner surface of head and block, which probably runs at or about coolant temp. So the engine inner surfaces serve as the oil cooler.
(at least, it seems likely to me)
cheers
Jay


Jay Maechtlen

http://www.laserpubs.com/techcomm