Steve Thomas
True Classic
which is why I was saying you don't want that
Turbo systems for X1/9's
- Thread starter Dr.Jeff
- Start date
Dr.Jeff
True Classic
Understood. If you consider what "and/or" is referring to, it was a comment on what it is capable of doing - for whatever reason. In other words something of a theoretical point. There may indeed be cases where a higher pressure might be desired. Perhaps not for a stock engine or whatever you may be thinking of, but nonetheless. However we are way off the point that was made about optional oil pumps to fit the SOHC.which is why I was saying you don't want that
Since pressure vs volume has been brought up again, it reminds me of a theory I posted once before (this came from one of the engineers I noted previously). The primary "resistance" that makes oil pressure in a engine is not the relief valve, but the engine's lubrication system beyond the pump - e.g. all of the galleries, bearing clearances, filter, and other points where pressure is lost as oil flows through the system. One illustration is the example of a extremely worn engine; resistance at the bearings is decreased and without added flow volume to make up for the oil loss, the pressure will drop. So the relief valve is actually a "bleed off" separate from the main oil supply going out of the pump. Much like the way a wastegate on a turbo relieves excess exhaust flow, the oil relief valve relieves any excess oil flow beyond what the system requires (assuming the pump provides more than required). In contrast, if the relief valve was located at the very tailend of a closed system (like a fuel pressure regulator) it would be different (which can be done on some engines' lubrication system).
With that in mind, increasing the opening threshold of the relief valve (i.e. higher spring pressure) manages the system pressure by way of allowing less excess oil flow to escape that system. The physics of that actually influences two effects of the overall system; pressure and flow (which are interrelated). When external accessories are added to the oiling system (such as a remote oil cooler, remote filter, and a turbo) they act like additional oil losses from the main galleries. There is now a greater demand for flow to maintain the desired pressure throughout the entire (extended) system at all times. Furthermore, the excessive heat that a turbo imparts onto the oil will reduce its viscosity causing additional pressure loss. Therefore, provided the pump has the potential to keep up, increasing the spring pressure on the relief valve can act to increase flow to the added external oil circuit(s) as well as the internal circuits. In other words help make up for the lost pressure caused by the added circuits (the greater the distance oil must travel, the greater the pressure loss) and increased heat.
But like any theory there are limitations; the increased relief setting could also cause higher than desired oil pressure when the oil is cold, at redline, and/or when there is not a lot of added demand. Obviously too much pressure will push oil past the seals. An externally adjustable oil pressure relief valve (as some engines have) would help to dial-in the 'sweat spot' for each non-stock engine build. But as has been stated several times, a higher volume of oil flow from the pump is the best answer. In the absence of a high volume pump we have to look at other means of protecting the modified, turbocharged engine. If for any reason increasing the relative rotation speed of the pump becomes too difficult to accomplish, then increasing the system pressure appropriately may help (affordably/practically).
Steve Thomas
True Classic
yep, relief valve only sets maximum pressure and has no effect otherwise. "relief" says it all.Understood. If you consider what "and/or" is referring to, it was a comment on what it is capable of doing - for whatever reason. In other words something of a theoretical point. There may indeed be cases where a higher pressure might be desired. Perhaps not for a stock engine or whatever you may be thinking of, but nonetheless. However we are way off the point that was made about optional oil pumps to fit the SOHC.
Since pressure vs volume has been brought up again, it reminds me of a theory I posted once before (this came from one of the engineers I noted previously). The primary "resistance" that makes oil pressure in a engine is not the relief valve, but the engine's lubrication system beyond the pump - e.g. all of the galleries, bearing clearances, filter, and other points where pressure is lost as oil flows through the system. One illustration is the example of a extremely worn engine; resistance at the bearings is decreased and without added flow volume to make up for the oil loss, the pressure will drop. So the relief valve is actually a "bleed off" separate from the main oil supply going out of the pump. Much like the way a wastegate on a turbo relieves excess exhaust flow, the oil relief valve relieves any excess oil flow beyond what the system requires (assuming the pump provides more than required). In contrast, if the relief valve was located at the very tailend of a closed system (like a fuel pressure regulator) it would be different (which can be done on some engines' lubrication system).
With that in mind, increasing the opening threshold of the relief valve (i.e. higher spring pressure) manages the system pressure by way of allowing less excess oil flow to escape that system. The physics of that actually influences two effects of the overall system; pressure and flow (which are interrelated). When external accessories are added to the oiling system (such as a remote oil cooler, remote filter, and a turbo) they act like additional oil losses from the main galleries. There is now a greater demand for flow to maintain the desired pressure throughout the entire (extended) system at all times. Furthermore, the excessive heat that a turbo imparts onto the oil will reduce its viscosity causing additional pressure loss. Therefore, provided the pump has the potential to keep up, increasing the spring pressure on the relief valve can act to increase flow to the added external oil circuit(s) as well as the internal circuits. In other words help make up for the lost pressure caused by the added circuits (the greater the distance oil must travel, the greater the pressure loss) and increased heat.
But like any theory there are limitations; the increased relief setting could also cause higher than desired oil pressure when the oil is cold, at redline, and/or when there is not a lot of added demand. Obviously too much pressure will push oil past the seals. An externally adjustable oil pressure relief valve (as some engines have) would help to dial-in the 'sweat spot' for each non-stock engine build. But as has been stated several times, a higher volume of oil flow from the pump is the best answer. In the absence of a high volume pump we have to look at other means of protecting the modified, turbocharged engine. If for any reason increasing the relative rotation speed of the pump becomes too difficult to accomplish, then increasing the system pressure appropriately may help (affordably/practically).
Bjorn Nilson
True Classic
I want higher pressure at low revs and a bigger pump would probably fix that. With UT gearing my car revs 3k rpm@110 kmh (68.4 mph). An oil pressure of 3 bar@3k rpm is to little IMO. When going far from home, it happens that I cruise at 4-4.5k rpm for hours (4-4.5 bar pressure) so more pressure/flow would be beneficial.
But this is also related to oil temperature/viscosity and my experience is that a (heavily) tuned UT engine constantly running at high revs/high temperstures works better with SAE 50 oil as this increases the oil pressure a little bit.