how much oil pressure is to much?

[David Redszus]

If you use an internal bypass, any free air from the sump has a longer and greater opportunity to enter solution. When the air enters solution in the oil the oil will behave as a fluid rather than an emulsion or mixture of air bubbles and oil -- providing that the pressure on that system is continued sufficient to keep the dissolved quantity of air in solution.

Well said. And of course, when the oil reaches the crankshaft passage ways, it drops in pressure releasing the gas in solution.

[Kevin Johnson]

If you use an internal bypass, any free air from the sump has a longer and greater opportunity to enter solution. When the air enters solution in the oil the oil will behave as a fluid rather than an emulsion or mixture of air bubbles and oil -- providing that the pressure on that system is continued sufficient to keep the dissolved quantity of air in solution.

Well said. And of course, when the oil reaches the crankshaft passage ways, it drops in pressure releasing the gas in solution.

It depends on how much air is in solution. If there is a 1 bar drop in the passage (say) but the remaining net pressure is sufficient to hold the gas in solution then it will not evolve. If you are constantly at a level of maximal volumes of gas driven into solution then there is a design issue with the sump. It might be because you are being forced to use a sump that was never intended for high g-forces or you could be on the cusp of needing a dry sump. Suspension and tire advances over the last 50-60 years push many designs well past their limits.

[Billzilla]

This is probably worth a new thread instead of sidetracking this one but ....
I have sometimes wondered what the lowest pressure/volume of oil you could get away with is. It's based on two-stroke engines, which have the lubricating oil mixed in with the fuel and it seems to lubricate the bearings & surfaces in a pretty haphazard fashion. I'm the first to admit I don't know a lot about two-stroke engines but I'm guessing they have a fair bit lower BMEP than a good four-stroke and so wouldn't tend to hurt the bearings as much anyway but there's still far less lubrication going on than in a four-stroke.
Or am I wrong?

[exhausted]

I just want to point out that it is possible to have oil pressure and no flow at all...

The fact that a engine continues to run and not seize up is proof that you have flow, but unless one has a oil flow meter, you really do not know jack.

And in a perfect situation (as David is pointing out) you do not want to have to bypass internally at all as it is wasted energy, read power.

[Kevin Johnson]

http://www.google.com/patents/US6763797 Instrument that with sensors on the slide and have no bypass and computable real time flow volume.

[David Redszus]

http://www.google.com/patents/US6763797 Instrument that with sensors on the slide and have no bypass and computable real time flow volume.

Let us suppose a main bearing of 2.20" diameter, and a bearing clearance of .003"; oil supply pressure is 74.7 psi and oil sump pressure is atmosphereic (14.7psi), and the oil has a viscosity of 6.0cSt. The oil flow orifice area would be .0207 sqin per bearing.

Now it is possible to compute the volume of oil that can be pumped through the engine (at least the mains), at any given oil pressure and viscosity. The same can be computed for cam bearings, rod bearings, etc.

An oil pump that is supplying more oil volume than can be accomodated by the engine oil flow capacity is simply wasted and turned into heat and aerated engine oil.

[Brian P]

This is probably worth a new thread instead of sidetracking this one but ....
I have sometimes wondered what the lowest pressure/volume of oil you could get away with is. It's based on two-stroke engines, which have the lubricating oil mixed in with the fuel and it seems to lubricate the bearings & surfaces in a pretty haphazard fashion. I'm the first to admit I don't know a lot about two-stroke engines but I'm guessing they have a fair bit lower BMEP than a good four-stroke and so wouldn't tend to hurt the bearings as much anyway but there's still far less lubrication going on than in a four-stroke.
Or am I wrong?

Two-stroke engines have completely rolling-element bottom ends. Ball bearings and roller bearings require only trace amounts of oil and it need not be supplied under pressure. The piston rings are lubricated by the oil mist.

Four-stroke engines that have rolling-element bottom ends don't require pressure lubrication, either. Traditional Honda single-cylinder motorcycle engines are like this. They have an oil circulating pump, but no appreciable pressure. The camshaft is supported on ball bearings, and the camshaft has a central oil passage that is fed from the oil circulating pump, and there is an oil-squirter hole on each cam lobe that coats the rocker arm with oil just before the cam lobe starts pushing on it. Oil spraying everywhere in the cylinder head is enough to lubricate the rocker pivots and the valve stems.

Honda four-stroke singles are normally very durable engines.

[Belgian1979]

If you use an internal bypass, any free air from the sump has a longer and greater opportunity to enter solution. When the air enters solution in the oil the oil will behave as a fluid rather than an emulsion or mixture of air bubbles and oil -- providing that the pressure on that system is continued sufficient to keep the dissolved quantity of air in solution.

Well said. And of course, when the oil reaches the crankshaft passage ways, it drops in pressure releasing the gas in solution.

Thus you need a higher pressure to prevent this from happening and that you loose some power because of that is not relevant in view of better oiling of the crank and rods ?

[Belgian1979]

Besides parasitic drag, what other problems am I going to have if we try running this engine the way it is?

Excessively high oil pressure will increase pumping losses. But there is much larger problem with excesive oil pressure; oil aeration. When the pressure relief valve opens, oil is returned to the sump in a very aerated form. This reduces the oil density, reduces the thermal transfer properties of the oil and becomes a form of oil starvation. Even if the oil pressure is maintained.

It has become standard practice to run oil pressure readings into a data logger and plot against engine rpm. The oil pressure should increase linearly with rpm. When the pressure curve flattens, the oil relief valve is dumping oil and the aeration process has begun.

Excessively high oil pressure has never helped an engine. Using the right oil viscosity at the right temperature is the life blood of an engine.

[cadamzak]

Will cam bearing orientation change the oil pressure? If so how much of an increase can you see by this?

[Kevin Johnson]

Will cam bearing orientation change the oil pressure? If so how much of an increase can you see by this?

When you dropped the pan and pulled the pump to check the pressure relief valve spring, what was the free length, wire diameter and number of coils? Could you see any color marking on the spring? Any spacers added?