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Royal Purple HPS. It contains the elevated levels of Zinc and Phosphorous to give the high film strength needed to properly lubricate the valvetrains.
Plus it's a full synthetic and it comes in the 20W50 recommended weight.
First time I put it in the car it ran smoother...no joke...having oil with the correct film strength is a big deal...you can add ZDDP (that's the compound name..don't ask me what it all stands for) to any oil..but I prefer this cause it's simpler...plus it's made for the older engines like ours that need it..great stuff.
I'm thinking it should protect well in cold starts given 10w, about 1000 ppm of Zinc, and other cold-start wear protection compounds. Then when hot it should flow about the right amount while protecting parts adequately.
I couldn't find ZDDP specs for the Ligui Moly 10w-60 when I looked the other day at their web site. Provided that the ZDDP is in the 'just-right' window as reported above, I 'spose it should work fine. I would double check the various other certifications and make sure they're consistent with what the engine spec is per factory. 60 weight seems a bit over-kill maybe. I'm sure, though, that you've thought about flow rates versus pressure at the engine's designed operating temperature of ~196F. On the flip side, we know that there's too much oil flow at high rpms.
This answers one of my other questions:
Originally Posted by ptuomov
I've got ball bearing turbos that are cooled with engine coolant, and an electric auxiliary water pump and an electric oil scavenge pump that run for a period after engine shut down, so I'm thinking that these turbos don't put any additional requirements on the engine oil. Just based on common sense.
Since you've got after-run for coolant and oil you shouldn't have to worry (much) about the oil getting heat-soaked after shutdown. Obviously, bay temperatures shoot up after shutdown since there's no active cooling (modulo your pump's after-run.)
I'm reminded of a story from a factory Audi tech about A4s in the mid-2000s: They had a big oil line that ran behind the engine and over the exhaust manifold. This led to serious oil sludge issues since - I assume - there was no after-run for moving the oil around after shutdown and the oil got heat-soaked.
Also, isn't ZDDP something that gets consumed by cold starts and metal to metal contact? That is, as long as there's a high enough concentration which may not have to be very high at all, the extra ZDDP is just going increase the required oil change interval? That's a question, not a statement: I don't really understand all these issues as well as I'd like to.
Based upon some papers I skimmed a couple of years ago, the ZDDP actually reacts with the base oil (or grease) and 'goes away' with time. None of the papers I found provided enough data on how long it takes for me to form something that could easily fit in this context. I was, at the time, mostly interested in forming an opinion of the state of the grease in all of our seal bearings (which was: no ZDDP after 20+ years.)
Of course, the higher heat and additional load from making more power add to the oil requirements but not directly in terms of turbocharger lubrication. Common sense tells me that the oil will likely run hotter if the rod bearing loadings under compression are three times higher than stock and the engine makes three times as much power. That's why I'm kind of thinking that SAE 60 hot viscosity might be the right pick.
Add in how much of that power gets turned into heat before it gets turned into heat on the pavement through the wheels. I don't recall if you've increased oil cooling capacity? I assume you've got some oil temperature monitoring capability?
No matter what data, papers, or other wisdom that might shed light on this thermo issue, I'd want to change the oil early and often. Possibly coolant too.
Used oil analysis' will likely shed light on how the oil behaves over time and allow the loop to be closed.
I think (but do not know) that ZDDP gets consumed when there's metal to metal contact in a mixed or worse lubrication regime. The exact way it gets consumed is a bit of a mystery to me, but I think that ZDDP decomposes under simultaneous heat and pressure and the resulting zinc phosphate layer acts as a sacrificial (softer) metal coating. This should happen, for example, on the lifter and cam lobe at low rpms. The phosphorus and zinc continue to exist in the oil even after ZDDP has been consumed, but just not as ZDDP, and possibly zinc is not in suspension anymore. If this is true, then isn't it the case that more ZDDP would be providing longer protection but not better protection. Furthermore, if my speculation is right, elemental analysis of oil such as mass spectrometer "burns" the ZDDP, zinc, and phosphorus at something like 10,000 F using plasma and by my logic one can't tell the difference between available ZDDP and already consumed ZDDP and the resulting zinc and phosphorus. Thus, I don't know how to measure the depletion of ZDDP.
By the way, my current opinion is that the oil test data on the page maintained by "540 Rat" is very relevant for mixed and worse lubrication regimes, such as camshafts-lifter interfaces. However, for bearings that are intended to be mostly in hydrodynamic lubrication regimes, such as rod bearings, my current thinking is that the correct (hot) oil viscosity is more important than any test results from tests that mimic the mixed lubrication regime.
The reason why I'm wobbling between lower viscosity and higher viscosity oil is load-bearing ability vs. cooling. Viscosity*bearing speed / bearing pressure is a design value for bearings such as rod bearings. If I am increasing the peak load on the bearing by say 50% (the average load is going up by a lot more), then to keep the bearing as far from mixed lubrication regime as stock I'd have to also increase viscosity by 50%. One probably will have to take some more risk, but clearly the higher peak loads on the engine point towards higher that stock oil viscosity.
Offsetting this load consideration is that higher viscosity oil causes more friction and more heat in the bearings. At the same time, the flow rate is going down and heat transfer from the bearings thus also down (for a given temperature differential). With higher viscosity oil, oil will be running hotter and the bearings hotter yet. So cooling is an important problem: I'll have to be able to cool the oil in order to run high enough viscosity that can protect the engine.
You asked about the cooling system. As of now, there aren't many cooling system modifications. Both the free-flow intake upstream of the compressor and the free-flow exhaust downstream of the turbo help cooling. The engine is "fuel cooled" at full load like all turbo cars were until the GDI-VVT cars. And there will be a big-*** oil cooler in the stock GT cooler location that will be correctly ducted to the airflow. The feature of adding a thicker aluminum radiator is protected in the fan shroud design, but I haven't done anything on that yet as I believe that air flow thru the radiator is a bigger problem for 928 that the radiator size per se. Finally, I'm just going to "improve" cooling by simply running the engine somewhat hotter than stock.
There's one more viscosity related question. Higher viscosity oil drains slower to the sump. The engine oil pump also ingests oil from the pickup at a lower rate if oil has higher viscosity. It's probably a wash in normal situations. However, when the car is under severe g-load, perhaps the oil can't drain to the sump. In this case, I am thinking that higher viscosity oil has a longer lifeline under those high g-forces because the oil pump sucks the sump dry slower.
By the way, me figuring out this stuff is very much work in progress. For anyone reading this, consider the possibility that I'll flip flop again like this guy when I learn something unexpected:
Here's a post by a person on speedtalk.com who makes sense to me on the topic of oil viscosity:
Re: Symptoms of too high or too low motor oil (hot) viscosity
Postby mekilljoydammit » Thu Jan 12, 2017 9:55 am
I'm going to basically keep this at a high school level - IE, this is what affects what and why, but leaving out the math. I hate doing appeals to authority, especially when I'm setting myself up as the authority, but when I was doing the R&D stuff we had 3-4 people with doctorates and years of experience in the field doing the simple version of the computer code to figure out this stuff. The code they came up with got increasingly less accurate the closer to the limit things were loaded to, and that's much simpler scenarios (more mechanically complicated designs, sure, but basically static loads) than we're seeing in engine bearings. I may have picked their brains as much as I could, but I don't know nearly as much as they do, so I'm not going to pretend I'm up to coming up with mathematical solutions, you know?
Knock does interesting things actually - I think I've seen examples where the top (piston side) rod bearing was the one damaged! If the bearing has to shift relative to the shaft all of a sudden, there's going to be a sudden pressure drop on the unloaded side where air will come out of suspension and the oil may drop below its vapor pressure - cavitation in other words. Then when things catch up, the oil collapses all those bubbles and the water hammer effect erodes material away... in addition to the possibility of breaking through the film on the other side, of course.
Air entrainment is a huge issue too, but I do really agree that oil temperature is something that needs to be controlled. Too far in either direction on hot viscosity (that is to say, viscosity of what's actually getting to the bearings) can lead to runaway situations - too thick and there's too much heat generation, not enough flow to pull heat away, and localized hot spots kill your bearings, too thin and the film gets too thin, there's excess heat generation and hot spots kill your bearings. Fortunately, in the real world, viscosity of oils that you would put in your engine don't vary enough to produce really disastrous effects - for applications where you're not on the ragged edge, going a bit too thick will just mean that it gets a little hotter, the viscosity comes down and it self corrects, albeit at a little more friction than optimal, too thin may mean that it doesn't heat up quite as much, etc. As a rule of thumb, I'd prefer to err on the side of too thick for stuff that's getting flogged (I come from an amateur roadrace background) because of the next issue.
See, the next issue is rod bearings. First, an ideal bearing looks like a crank setup - fed from the side, everything goes out. In this situation, engine speed has no bearing (ha!) on oil flow, and actually if you have thin oil (thinner than you'll see on any car) you can get away with incredibly small supply pressures if the flow is enough. The problem is rod bearings are fed from the crank. By the nature of the drillings, the oil has to fight centrifugal force to get to the center (most cranks) or a bit in from the journal (Cosworth style drillings) and that reduces the effective pressure. Worse, if the effective pressure at the part of the drilling closest to the center of the crank gets below the vapor pressure of the air/oil mixture you're actually feeding everything, you just starved your rod bearings completely. Intuitively you might think that centrifugal force flinging out to the rod pins would help, but it's kind of a "you can't push a rope" thing - or more scientifically, once you get below the vapor pressure, it's not liquid anymore. This is why, btw, Formula 1 does things like feeds the crank from the nose, and why they were experimenting with hollow cranks with big oil reservoirs in each main.
If I was Roush or Cosworth or someone and was trying to do this, what I'd do is have a bunch of thermocouples embedded in any bearing I could get to, plus in the path of the oil coming out of the bearings, then do endurance testing at high loads - race track simulation on an engine dyno at realistic oil temps ideally. Make sure nothing is getting too hot during the test and then do a test program with teardowns between each rebuild distance and stepping oil viscosity to the minimum that will avoid wear. What I do for race stuff in the real world where I have to pay for it is run somethingW50 and go bigger on the oil cooler.
Originally Posted by worf928
I couldn't find ZDDP specs for the Ligui Moly 10w-60 when I looked the other day at their web site. Provided that the ZDDP is in the 'just-right' window as reported above, I 'spose it should work fine. I would double check the various other certifications and make sure they're consistent with what the engine spec is per factory. 60 weight seems a bit over-kill maybe. I'm sure, though, that you've thought about flow rates versus pressure at the engine's designed operating temperature of ~196F. On the flip side, we know that there's too much oil flow at high rpms.
Based upon some papers I skimmed a couple of years ago, the ZDDP actually reacts with the base oil (or grease) and 'goes away' with time. None of the papers I found provided enough data on how long it takes for me to form something that could easily fit in this context. I was, at the time, mostly interested in forming an opinion of the state of the grease in all of our seal bearings (which was: no ZDDP after 20+ years.)
Add in how much of that power gets turned into heat before it gets turned into heat on the pavement through the wheels. I don't recall if you've increased oil cooling capacity? I assume you've got some oil temperature monitoring capability?
No matter what data, papers, or other wisdom that might shed light on this thermo issue, I'd want to change the oil early and often. Possibly coolant too. Used oil analysis' will likely shed light on how the oil behaves over time and allow the loop to be closed.
when hot pressure is always from 3 bar on, no more valve lifters noise after winter hibernation, car sometime uses oil, sometime not(up to a liter every 1000km, sometimes a liter every 800kms, sometimes 3000kms and I need to refill 0,5 liter.....randomly), with liqui-moly engine is not oil thirsty (worst scenario 1 liter after 1000kms, 350 high speed on german autobahn when I went to Porsche museum last summer).
Zddp content should be about 800-1000.not much, but good.
I use liqui moly 10w60 on my '92 GTS. when hot pressure is always from 3 bar on, no more valve lifters noise after winter hibernation, car sometime uses oil, sometime not(up to a liter every 1000km, sometimes a liter every 800kms, sometimes 3000kms and I need to refill 0,5 liter.....randomly), with liqui-moly engine is not oil thirsty (worst scenario 1 liter after 1000kms, 350 high speed on german autobahn when I went to Porsche museum last summer). Zddp content should be about 800-1000.not much, but good.
Liqui Moly Synthoil Race Tech GT1 10W-60 will be going into my turbo car after the break-in oil is out. Now, importantly, any negative experiences with Liqui Moly 10W-60, either experienced personally first hand or heard second hand stories?
when hot pressure is always from 3 bar on, no more valve lifters noise after winter hibernation, car sometime uses oil, sometime not(up to a liter every 1000km, sometimes a liter every 800kms, sometimes 3000kms and I need to refill 0,5 liter.....randomly), with liqui-moly engine is not oil thirsty (worst scenario 1 liter after 1000kms, 350 high speed on german autobahn when I went to Porsche museum last summer).
Zddp content should be about 800-1000.not much, but good.
Siscogts my 928 does same....harder I drive...it will use some. If I keep it below 4,500 it hardly uses anything...if I spend a lot of time over 5k I can go through a good bunch.
Sorry: e-mail notifications of new posts are intermittent at best.
Originally Posted by ptuomov
I think (but do not know) that ZDDP gets consumed when there's metal to metal contact in a mixed or worse lubrication regime.
I agree: I think this is the case, but do not know for certain. I am more certain that ZDDP will decompose over (long) time regardless of mechanical gyrations.
The exact way it gets consumed is a bit of a mystery to me, but I think that ZDDP decomposes ... If this is true, then isn't it the case that more ZDDP would be providing longer protection but not better protection.
Except for the references you supplied above that indicate that too much of a good-ZDDP-thing is, like many non-ZDDP things in life, not good at all.
Furthermore, if my speculation is right, elemental analysis of oil such as mass spectrometer "burns" the ZDDP, zinc, and phosphorus at something like 10,000 F using plasma and by my logic one can't tell the difference between available ZDDP and already consumed ZDDP and the resulting zinc and phosphorus.
But, hey, it's good enough for Generic Drug Manufactures to prove equivalence so why isn't it good enough for you? ... Opps. Wrong soapbox.
Thus, I don't know how to measure the depletion of ZDDP.
One might speculate that the ZDDP constituents, once 'consumed' by whatever process, might have an effect on the other oil-analysis-measureable characteristics of the oil. I would further speculate that the guys at Blackstone might have something to say on this topic. I know for a fact that they're happy to talk on the phone about oil, analysis, and thick streams of metal bits flowing through 928 engines. If you talk to them report back...
By the way, my current opinion is that the oil test data on the page maintained by "540 Rat" is very relevant for mixed and worse lubrication regimes, such as camshafts-lifter interfaces. However, for bearings that are intended to be mostly in hydrodynamic lubrication regimes, such as rod bearings, my current thinking is that the correct (hot) oil viscosity is more important than any test results from tests that mimic the mixed lubrication regime.
Ok. Do we (you) know the correct viscosity for our bearings? Or do we simply assume that the engineers at Porsche in the early 70s got it right (enough) and that 50w is the higest viscosity we should run? And that the hot viscosity of a 50w oil in 197* is more-or-less the same as it is 40 years later?
But, let's add more force...
The reason why I'm wobbling between lower viscosity and higher viscosity oil is load-bearing ability vs. cooling. Viscosity*bearing speed / bearing pressure is a design value for bearings such as rod bearings. If I am increasing the peak load on the bearing by say 50% (the average load is going up by a lot more), then to keep the bearing as far from mixed lubrication regime as stock I'd have to also increase viscosity by 50%.
Is it a linear relationship? Does a 50% increase in bearing load require a 50% increase in viscosity? Nature abores a vacuum. And, in my expierience, linearity.
I'm not a tribologist. I didn't even stay at a Holiday Inn last night. The best I can do is to ask questions.
One probably will have to take some more risk, but clearly the higher peak loads on the engine point towards higher that stock oil viscosity.
Why is it that my 991TT uses 0-40w oil? The bearing loads are significantly higher than a stock 928 running x-50w.
So cooling is an important problem: I'll have to be able to cool the oil in order to run high enough viscosity that can protect the engine.
I'm convinced that you need more oil cooling that a stock 928 simply because you've got more opportunities outside of the engine bearings to heat the oil. And because you've got 2x or more the amount of heat to remove from the engine bay. I'm not convinced that you need 60w oil (that would further exacerbate your cooling requirements due to flow vs. temp, etc.)
And there will be a big-*** oil cooler in the stock GT cooler location that will be correctly ducted to the airflow.
Hmmm... I would expect nothing more than a slightly-less-than-medium-assed-sized oil cooler given the constraints of the stock GT/GTS location.
The feature of adding a thicker aluminum radiator is protected in the fan shroud design, but I haven't done anything on that yet as I believe that air flow thru the radiator is a bigger problem for 928 that the radiator size per se.
Air flow can be traded-off, a little bit, by HEX surface area. But, yes, the 928 is 'cooling limited' in the front. I have mild issues with the twin-screw in certain speed/rpm/ambient regimes that could be fixed with either cooler air, or more air (or more rpm.)
Finally, I'm just going to "improve" cooling by simply running the engine somewhat hotter than stock.
Hmmm... how much hotter?
There's one more viscosity related question. Higher viscosity oil drains slower to the sump. The engine oil pump also ingests oil from the pickup at a lower rate if oil has higher viscosity. It's probably a wash in normal situations. However, when the car is under severe g-load, perhaps the oil can't drain to the sump. In this case, I am thinking that higher viscosity oil has a longer lifeline under those high g-forces because the oil pump sucks the sump dry slower.
I have a feeling you might be far out on the margins here. How much slower does 50w flow in a normal engine than your (prospective) 60w oil running in a hotter-than-stock engine? There's already massive oil flow through the engine - unless you've done something to restrict it.
Thinking further about it.... your 2.20 rear end means you're not getting the same coolant flow rate as my GT. It doesn't necessarily help to have more air or more HEX area, if the coolant can't run through the system fast enough.
Here's a post by a person on speedtalk.com who makes sense to me on the topic of oil viscosity:
Some sense yes. But, as many questions as things that might turn into answers.
Ok. Do we (you) know the correct viscosity for our bearings? Or do we simply assume that the engineers at Porsche in the early 70s got it right (enough) and that 50w is the higest viscosity we should run? And that the hot viscosity of a 50w oil in 197* is more-or-less the same as it is 40 years later?
I think that the hot viscosity number is measured at 100C/212F and it has basically been the same standard for a long time.
The SAE grade 60 has a viscosity range of 21.9 - 26.1 mm^2/s. Grade 50 has range 16.3 - 21.9 mm^2/s. LM 10W60 is right at the middle of the range at 24.0 mm^2/s.
I think that newer oils have better or equal high shear high temperature behavior in that they maintain a higher viscosity at 150C. So my guess (not a fact) is that one would not need to go higher viscosity grade because of that changing high temperature specification.
Originally Posted by worf928
But, let's add more force... Is it a linear relationship? Does a 50% increase in bearing load require a 50% increase in viscosity? Nature abores a vacuum. And, in my experience, linearity. I'm not a tribologist. I didn't even stay at a Holiday Inn last night. The best I can do is to ask questions.
I think the idealized formula says its proportional. Given the physical bearing attributes, such as journal roughness, bearing roughness, bearing length, radial clearance, journal diameter, eccentricity, etc. the lubrication regime depends on the Hersey number. Hersey number is (bearing speed * absolute viscosity) / pressure. To me, and I'm not a tribologist or even a garden variety mechanical engineer, this suggests that 50% increase in load will require 50% increase in viscosity to restore the Hersey number and the previous x-axis on the Stribeck diagram.
So it seems to me that if you increase the peak load by say 50%, and if the engine was previously well matched with the oil, some increase in the oil viscosity might be in order?
Originally Posted by worf928
Why is it that my 991TT uses 0-40w oil? The bearing loads are significantly higher than a stock 928 running x-50w.
I don't know. Different physical bearing dimenstions?
Originally Posted by worf928
I'm convinced that you need more oil cooling that a stock 928 simply because you've got more opportunities outside of the engine bearings to heat the oil. And because you've got 2x or more the amount of heat to remove from the engine bay. I'm not convinced that you need 60w oil (that would further exacerbate your cooling requirements due to flow vs. temp, etc.)
The first priority is to protect the bearings. Once that's done as efficiently as possible, then the next step is to remove whatever heat needs to be removed. The question here is not whether I want to protect bearings but what's the most efficient way to do it. How close to the limit is the SAE 50 oil in the stock engine? I don't know the answer. But once that answer is found, then it's time to add whatever cooling is needed to control the oil temperature.
Originally Posted by worf928
I have a feeling you might be far out on the margins here. How much slower does 50w flow in a normal engine than your (prospective) 60w oil running in a hotter-than-stock engine? There's already massive oil flow through the engine - unless you've done something to restrict it.
Van Rossum’s drainage theory says that the retained volume is proportional to the square root of the ratio of kinematic viscosity to total drain time. So that gives one some idea how long the drain takes if say the heads fill with oil in cornering. Of course, I think it's more of a gas flow problem than direct oil flow problem, so this is pretty much irrelevant in my opinion...
In terms of the pump demanding oil, assuming that the relief valve is cycling it should be about inversely proportional to viscosity. So if SAE 50 oil has viscosity of 19 and SAE 60 oil has viscosity of 22, the flow rate is about 16% faster? This assumes the same temperature. That I mean as a ball park starting point?
These aren't answers, these are just demonstrations that the magnitudes _could_ be large enough to be relevant.
Hello,
Thank you for all these information!
I used to use Elf evolution 900 5W40. But I realized :
- looks to be too thin,
- not a huge oil consumption but I found a lot of oil in my intake, a lot of knocks during knock count...
However, I did not notice any evidence of wear while removing cam covers and oil pan.
So in addition to incorporation of Greg Brown baffles (crankcase and cam covers), I'm changing my oil.
Greg recommend Brad Penn 20W50 or Torco 20W50. Most of you use Mobil 1 15W50. Some of you (and someone I know that is always beating most cars on track with its old stock S2) are using 10w60...
Not easy to choose... but I can't convince myself to put 20w50... It was what I was using on my first car... and it is the only one I ever saw smoking blue... After that I only used synthetic oil... Too hard for me to go back mineral so far... one day maybe...
So, Brad Penn : 40° viscosity : 159, 100° viscosity 20 and HTHS 150° : 6.2
Torco : 40° viscosity : 189, 100° viscosity 21.3
So I checked all 10w60 oils available here and the mobil 1 10w60 extended life caught my attention :
- 40° viscosity : 153, 100° viscosity 22.7 and HTHS 150° : 5.7,
- synthetic but regular ZDDP (1300),
- in conclusion this oil looks good for the 928 : important characteristics very close to 20w50, 100° viscosity in the lower side of the tolerance, so very close to 20w50 upper tolerance (close to torco so thick enough but not too thich), good zinc level.
I did use torco tr 1 20 50 but when ambient temps get above 95 the oil pressure lite came on at times,,,,,switched to amsoil 20 50 and pressure always 2 bar no matter the temps and have stuck with it for the last 7 yrs....
Liqui Moly Synthoil Race Tech GT1 10W-60 will be going into my turbo car after the break-in oil is out. Now, importantly, any negative experiences with Liqui Moly 10W-60, either experienced personally first hand or heard second hand stories?
Today my 3rd oil change, keep on putting liqui moly 10w60. I removed valve covers for new tensioner pads and new powder coating on covers. Camshafts look to be in good conditions, no unusual wear, no pitting. Maybe 3 oil changes in 6 years and 14 k kms ( + I added 6 liters,cause gts oil ingestion) and 60 weight is really overkill, I cannot tell something about long term protection of this oil.