10psi/1000rpm rule and running lower viscosity oil

[XS650]

Originally Posted By: RangerGress
I reread the posts and found some confusion. I was testing the 10psi/1000rpm rule. I was not testing 10psi @ 1000rpm. I was testing the relationship, and doing so at 3k rpm.


Your only error is assuming that some ancient rule of thumb overrides what the engine designers recommend.

The only thing that such that such cockamamie ROTs prove is how tolerant engines are of abuses by clueless people.

Based on AEHass's judgment on automotive lubrication recommendations, I [censored] sure wouldn't let him anywhere near me with surgical tools in his hands.

 

[Steelhead]

is this Beemer a race car in competition to win or a protected garage queen?

 

[Doug Hillary]

Hi,
As others have said a rule of thumb is that – the Engineering rules of engine design overwhelm the thumb!

In a recent survey of around 100 engines from the same engine family I oversaw showed a remarkable similarity in OP readings beyond a hot idle!

The lubricants used varied from 10W-30 to 25W-70 in both mineral and synthetic form - the engine maker specifies either a 0W-40 or a 5W-40 synthetic

The oil pressure at idle varied from 22 psi to 50psi - this was an indication of flow! Synthetics showed a lesser pressure by an average of around 7psi and of course the lighter viscosities did too. The manufacturer specifies around 22psi at a hot idle and at least 73psi at 5000rpm - hot

At 4000 rpm all engines were above 60psi and very close to each other – the by-pass on these engines is set at around 118psi. The various viscosities had effectively no impact at all above around 2500-3000rpm

Engines with complex valve trains and other mechanisms will always need a higher pressure to circulate through the structures involved. The flow of course is the key to this – pressure is needed to deliver the lubricant – flow will always be constant per revolution of the engine

In modern heavy high speed diesel engines it is common to see 22psi at hot idle and 44psi at 1800rpm – the point at which they work most at!

In the end the Design Engineers determine the pressure and flow needed for suitable all round use – and I have never seen them use their thumbs!

I like them would be concerned that the lubricant used had the correct HTHS viscosity for the designed application!

Electrically operated and controlled supply and scavenge oil pumps are about to change the rules of the game. Constant OP may become a reality as needed and flow will be dependent on need too!

And the rule of thumb will remain just that – a rule for thumbs!

 

[AEHaas]

Where the "rule" is helpful is to show that it is your application that determines your needed viscosity. I do not run my Enzo at 200 MPH so the oil never gets very hot. In fact it is hard to get it above 180 F any way that I drive. This is with 0W-30 oil as opposed to the Ferrari recommended 10W-60. I get around 70 - 80 PSI at 4,000 RPM around town. I get less than 1/2 the wear rates as compared to my neighbor running the OEM oil in his Enzo.

In my Ferrari Maranello 575 the manual stated that 75 plus PSI at 6,000 RPM was the test point. Red line was at 8,500.

The oil lines in both cars are around 1 inch ID. We are talking about a huge flow.

Pressure has nothing to do with bearing protection. The pressures only function is to deliver oil so the bearing is kept wet. As I have shown excessive pressure limits the flow at the pop-off valve at a lesser RPM minimizing the maximum flow rate.

aehaas

 

[Steelhead]

since most mass production passenger vehicles engines use a wet sump lift pump suction system, higher oil viscosity can and does limit oil pump pickup and flow rates

oil flow rates are critical in hi pro engines for cooling purposes, especially of the pistons.

thin to win races

 

[RangerGress]

I've read all the posts carefully and I don't see any consensus emerging, nor guidance that I can use. Which is a complaint directed at the complexity of life, not at you guys who are educating me here.

Surely there is a concrete way of identifying the right weight of oil. Like if, under track conditions, I get 60psi at 4000 rpm, then that is assumed to be adequate oil flow. Then I would be, in this example, free to reduce oil viscosity until I get 60psi at 4000 rpm.

Or maybe some combination of oil pressure and HTHS? Is HTHS a better measure then Viscosity at 100deg C, cST?

Note that it is a stock motor, per the requirements of the class.

Steelhead: The race car is competition to have fun, not so much to win. It is somewhat limited by the skills of it's driver. It does ~15 races and ~60 track days per year. We finish mid-pack.

See
http://www.NASA.com
http://www.SpecE30.com

Positively the most fun an American (or Aussie) will ever have.

 

[Lazy JW]

Originally Posted By: RangerGress
.... it gets run pretty hard. I don't want to swap the motor every year, but I could probably live with putting in a new (junkyard) motor every 3 yrs....


Seems to me that most of the replies about "manufacturer's recommendations" are ignoring the fact that this car is being used pretty far out of the norm. If everyone strictly adhered to the manufacturer's recommendations there would never have been a "performance industry" for the hot rodders.

Since you are (as stated above) willing to give up a bit of longevity for a bit of performance just go out there and give it a whirl; just keep careful watch of your oil pressure and see what happens. Only you can decide if the tradeoff is worthwhile, but it seems that you are going about this in a logical, carefully thought out manner.
Have fun,
Joe

 

[Steve S]

Originally Posted By: Gary Allan
UOA.

Don't take offense to SteveS. I've heard rumors that he works here composing captions. It's just his thing ..

Not there but it is my thing. Gary knows about stuff like that.

 

[RangerGress]

I just did some reading on HTHS and checked a number of different oils re. engine wear. Let me throw this idea out for debate....

One must be cautious about applying motor oil and engine wear studies to race cars. Most engine wear occurs at start up. Therefore many studies that focus on engine wear end up orienting on start up conditions, even if that was a specified intent.

The life of a race car engine is not one of enduring grueling startups.

So we have to be careful to not allow the discussion to be skewed by ideas drawn from start up conditions oriented data.

That makes sense? That change the significance of any of the previous posts?

 

[RangerGress]

Originally Posted By: Lazy JW
Originally Posted By: RangerGress
.... it gets run pretty hard. I don't want to swap the motor every year, but I could probably live with putting in a new (junkyard) motor every 3 yrs....


Seems to me that most of the replies about "manufacturer's recommendations" are ignoring the fact that this car is being used pretty far out of the norm. If everyone strictly adhered to the manufacturer's recommendations there would never have been a "performance industry" for the hot rodders.

Since you are (as stated above) willing to give up a bit of longevity for a bit of performance just go out there and give it a whirl; just keep careful watch of your oil pressure and see what happens. Only you can decide if the tradeoff is worthwhile, but it seems that you are going about this in a logical, carefully thought out manner.
Have fun,
Joe


I'd like to be able to do exactly that. But no consensus is emerging that states something like "if you get 60psi at 4000rpm, then you're good because that's the most important variable. 50psi at 4000 rpm might be a little low tho". That's clear guidance that I can employ.

Instead I think that I'm being told that I should not over-emphasize the importance of oil pressure/rpm.

It's hard to decide on a trade-off when the variables are understood only poorly.

I also read here that low viscosity is at it's worse in low rpm high load conditions. The car is almost never <3800rpm. So maybe the concerns re. low viscosity oil apply primarily to inapplicable low rpm conditions.

 

[Gary Allan]

Quote:
One must be cautious about applying motor oil and engine wear studies to race cars. Most engine wear occurs at start up. Therefore many studies that focus on engine wear end up orienting on start up conditions, even if that was a specified intent.


Please keep in mind that 'startup" is an exploited misnomer for anything before "steady state". It's typically 20 minutes in most engines. As Doug Hillary might tell you, some of the higher end Euro's spend their whole life in "startup" in non track useage if they don't stray too far from the farm/station.

 

[Gary Allan]

Originally Posted By: Steve S
Originally Posted By: Gary Allan
UOA.

Don't take offense to SteveS. I've heard rumors that he works here composing captions. It's just his thing ..

Not there but it is my thing. Gary knows about stuff like that.


Hey, pal. Do you think you reach iconic member status without liabilities??

 

[Steve S]

What does iconic mean?

 

[TallPaul]

If you are going thin and lower OP, use Redline brand oil as it will give you the HTHS of the next higher grade. I would think that would be a buffer for the start up condition and what little low rpm operation the engine does see.

 

[RangerGress]

More research indicates that BMW now prefers HTHS >3.5. Some folks are saying that this is linked to the longer oil change interval. How could they be linked? HTHS go down over time? Maybe due to gas blow-by?

Hard to understand why I should care about oil change interval.

I haven't read anything yet about what BMW spec'd 20yrs ago for a 1987 car.

 

[Ken2]

Always keep in mind that Dr. Haas is a cosmetic plastic surgeon, not a mechanical engineer. Yes, he's a smart guy. No, he is not an engine designer, tribologist, or anyone else with specialty engine and oil knowledge.

Dr. Haas has some fixations with oil flow. While I haven't read all his writings, so far I haven't found anything about the hydrodynamic wedge of oil that develops in every rotating journal bearing. This wedge of oil has very high pressure and keeps the moving parts apart...the oil pressure from the oil pump does not. Yes, oil flow carries heat away, as well as any debris particles, but does not keep moving parts apart.

So, real Dr. Haas' writings, go to him for a nose job, but follow the advice of the engineers who designed your engine when you pick an oil for that engine.

 

[XS650]

Gary, you mispilled ironic.

 

[RangerGress]

Originally Posted By: Ken2
Always keep in mind that Dr. Haas is a cosmetic plastic surgeon, not a mechanical engineer. Yes, he's a smart guy. No, he is not an engine designer, tribologist, or anyone else with specialty engine and oil knowledge.

Dr. Haas has some fixations with oil flow. While I haven't read all his writings, so far I haven't found anything about the hydrodynamic wedge of oil that develops in every rotating journal bearing. This wedge of oil has very high pressure and keeps the moving parts apart...the oil pressure from the oil pump does not. Yes, oil flow carries heat away, as well as any debris particles, but does not keep moving parts apart.

So, real Dr. Haas' writings, go to him for a nose job, but follow the advice of the engineers who designed your engine when you pick an oil for that engine.


I would like to follow the advice of the engineers that designed my engine. But no one seems to know what the engineers advice is. All we know is what the committee of accountants, marketers and lawyers approved. Accountants will tell you the hard truth of $$, even if you look at things differently. Marketers will lie like a dog, and lawyers want to ensure that it's always your fault.

 

[mechtech2]

Like many of said, the '10 lb' rule is only a general guide.
I don't want or need 75 lbs of oil pressure when I redline my car.

An oil temperature gauge added to your present knowledge will be your best friend concerning your specific needs. And be aware that WHERE you put the gauge sensor is important.

 

[Lazy JW]

Originally Posted By: RangerGress
.....

I would like to follow the advice of the engineers that designed my engine.....


That would be easy if you were operating in the "normal" manner. You aren't, however.

Originally Posted By: RangerGress

...... and lawyers want to ensure that it's always your fault.


Ultimately, whenever you step out of "normal" operating methods, it is indeed "your fault". Ya pays yer money and ya takes yer choices.

I strongly suspect that 35-40 psi at full boogey will not harm a thing; I would be uncomfortable with less than 10 psi at hot idle (this comes from years of experience driving old junkers that were thoroughly worn out and generally overloaded). Oil pressure is highly over-rated.
Let us know how it works.
Joe