how much oil pressure is too much?

[David Redszus]

Oil volume flow through the bearings is necessary to provide adequate cooling. The oil mass flow is given by:

M = CD * A * sqrt (p * P)

The flow area is a function of all oil flow orifices (bearings, spray jets, spray bars, etc).
The oil viscosity will affect the Cd value as will the geometry of all oil passages.
The oil density is a function of oil temperature and aeration for a given oil.
The pressure is the difference across any oil orifice.

The oil volume is dependent on bearing clearance and oil viscosity at the bearing operating temperature.
As bearing clearance increases, the flow orifice is increased allowing a greater outflow flow of bearing oil but with a resulting drop in oil pressure. Now it is necessary to increase oil pressure to maintain volume flow.

Assuming that bearing clearances are constant, oil mass flow will be determined directly by oil viscosity and with the square root of the oil density and pressure. Doublling the oil pressure will not result in twice the flow. The flow will increase by a factor of 1.4 not 2.0. Increasing oil pressure to 80 psi from 70 psi, will produce an incease in flow of only 6.7% (if all else remains unchanged).

Heat transfer is not the only parameter to consider. Bearing size, bearing loading, and rpm will determine the oil wedge that is required to maintain the film thickness necessary to keep rotating metal parts from touching each other.

Sliding surfaces are another story altogether.

It is important to take note of the oil temperature and oil pressure measurement location. Oil temperature should be measured at the point of entry to the bearings. Oil pressure should be measured where it is lowest in the engine oil circuit. Even better is to measure both in and out values for temp and press.

[rickseeman]

If you are still concerned, the old rule of thumb of 10 psi for every 1000 RPM has been a hot rod standard for decades and it has worked great. Many have found that with better control they can run far less than that and be just fine.

That rule is old school.
My premise is to consider engine torque over RPM. This means 10 psi for every 100ft/lbs of torque.

If I was to use the RPM based rule of thumb, I would have to run over 100 psi on a 10500 RPM Comp Eliminator engine!
With engines that turn 9700 RPM+, I have always set the pressure around 55~60 psi and never had a single issue.
Again, you have to consider the type of bearing, clearances and the oil pan design.

Torque? So on my mountain motor I need 120 psi? I don't think so and neither does Sonny. I think it has 40 psi.

[ap72]

If you are still concerned, the old rule of thumb of 10 psi for every 1000 RPM has been a hot rod standard for decades and it has worked great. Many have found that with better control they can run far less than that and be just fine.

That rule is old school.
My premise is to consider engine torque over RPM. This means 10 psi for every 100ft/lbs of torque.

If I was to use the RPM based rule of thumb, I would have to run over 100 psi on a 10500 RPM Comp Eliminator engine!
With engines that turn 9700 RPM+, I have always set the pressure around 55~60 psi and never had a single issue.
Again, you have to consider the type of bearing, clearances and the oil pan design.

Torque? So on my mountain motor I need 120 psi? I don't think so and neither does Sonny. I think it has 40 psi.

not to discount what you're saying but I'm sure your engine is built one hell of a lot better than mine, you probably spent more on the crank than I did on the entire engine, hell you probably spent more on just the oil pan.

Mine is just a mildly "souped up" LT1, 6500rpm max, cast crank, hyper pistons, hyd roller cam, King SI bearings- plain jane boring stuff that is NOTHING like the amazing machines some of you guys build and run. I have no ideas of ever winning a race with this thing, I just want it to give me 0 problems on the street.

[Kevin Johnson]

Heat transfer is not the only parameter to consider. Bearing size, bearing loading, and rpm will determine the oil wedge that is required to maintain the film thickness necessary to keep rotating metal parts from touching each other.

Don't forget the design of the oil passages in the crank. Depending on the design higher pressures could be needed as rpms rise. There are SAE papers on this particular aspect from GM. OP should be fine with heavy duty high volume high pressure pump if an OEM example can be found. At a minimum, I think he could expect that a GM engine combo using it has had a 50 hour durability test run on it.

Part of the problem is that when people read these threads there is a tendency to extrapolate too much to other engine designs. A good "paper" to read with respect to oil pressure in the crank circuits is the patent application for welded crankshafts by Mercedes (used in F1).

[racinnut15xm]

Which wet sump pump is everyone running for circle track stuff now days? I know a couple years back people had issues w/ the gears in some pumps, starting to gather stuff up to build a backup. Thanks

[900HP]

Which wet sump pump is everyone running for circle track stuff now days? I know a couple years back people had issues w/ the gears in some pumps, starting to gather stuff up to build a backup. Thanks

Melling select 10552c works for me (sbc)

[Olefud]

A good "paper" to read with respect to oil pressure in the crank circuits is the patent application for welded crankshafts by Mercedes (used in F1).

US Patent 6378396

[Kevin Johnson]

According to the present invention, the radial oil supply lines are located on the centrifugally inner side, overcoming the prejudice that oil delivery along the centrifugal force vector is necessary for proper lubrication. This aspect of the present invention stands in contrast to the crankshafts described in German Patent Document No. DE 195 36 349 C1 and European Patent Document No. EP 0 090 013 B1, whose oil supply lines each terminate on the centrifugally outer side of the crank journals.

[Fordracer347]

Mine is just a mildly "souped up" LT1, 6500rpm max, cast crank, hyper pistons, hyd roller cam, King SI bearings- plain jane boring stuff that is NOTHING like the amazing machines some of you guys build and run. I have no ideas of ever winning a race with this thing, I just want it to give me 0 problems on the street.

If I were building this engine I would use a standard M155 pump with a pickup to match and set at the right height to the pan. Your rotating assembly is fine. Standard clearances (0.002-0.0025) maybe even a bit less, 10-30 oil of your choice and you will have loads of fun street miles ahead with no issues

[nhrastocker]

Torque? So on my mountain motor I need 120 psi? I don't think so and neither does Sonny. I think it has 40 psi.

I should had been more specific...small block engines!!

I forgot when was the last time I worked on a big block...I enjoy the high pitch sound of a high RPM small block more.

[JoePorting]

If it ain't broke, don't fix it. Standard oil pumps have been working great on standard and race SBC's for over 50 years. Why mess that up? Your distributor gear will also like the standard oil pump too.

[ap72]

If it ain't broke, don't fix it. Standard oil pumps have been working great on standard and race SBC's for over 50 years. Why mess that up? Your distributor gear will also like the standard oil pump too.

"working great" is a relative term I guess. I use mostly moderate mileage used cores and every single one of them shows bearing wear. Not unusual catastrophic wear mind you, just the regular old "100,000 miles" bearing wear. I don't like that. My goal is to pull that engine apart at 100,000 miles and have the bearings look EXACTLY as they did when I pulled them out of the box. Good oil, good filter, good return, and good supply are my methods of getting there- the supply is what I'm trying to improve.

[900HP]

If it ain't broke, don't fix it. Standard oil pumps have been working great on standard and race SBC's for over 50 years. Why mess that up? Your distributor gear will also like the standard oil pump too.

"working great" is a relative term I guess. I use mostly moderate mileage used cores and every single one of them shows bearing wear. Not unusual catastrophic wear mind you, just the regular old "100,000 miles" bearing wear. I don't like that. My goal is to pull that engine apart at 100,000 miles and have the bearings look EXACTLY as they did when I pulled them out of the box. Good oil, good filter, good return, and good supply are my methods of getting there- the supply is what I'm trying to improve.

Excessive oil pressure won't help you with this. You need exact machine work and exact assembly. If you want the above you should also pre-heat the oil and coolant before starting and pre-lube the engine before cranking. Most wear is from start-up and cold oil. Once pressure comes up there is no metal to metal contact.

[ap72]

thank you for that tip. I may add an accumulator for that reason.

So to answer my original question it seems a 65lb spring is the max I would want to go?

[user-z68766209]

I'm looking at various high pressure springs for the standard sbc oil pump and I'm curious as to how high is too high? I know higher pressure means more parasitic loss but I'd rather trade that for dependability.

I see they have a 90lb spring... dare I venture that high?

If you do go that high with a wet sump...make sure you have a big pan and open up the oil retuns in the heads and block
good chance you could empty the pan and starve the pump.
Also IMO oil FLOW is key not pressure