Effect of viscosity on hydrodynamic engine bearing

[TKFD]

This is a great thread, and love how its getting down to the nitty gritty (tech term).

I have a question if I may. At the moment I am running 10W-40 full synthetic high ZDDP oil (Penrite 10tenths racing). After a hard run oil temps get to around 100degC (which isnt that high I know) and pressure drops from around 300kpa/44psi(warm) to about 200kpa/30psi (hot) at idle (1000rpm). Sometimes it drops a bit under 200kpa if I come straight off the track and let it idle and just sets off the low pressure 20psi warning light. It quickly restores after a cool down, and I have an oil cooler and on the cool down lap it drops quite a bit, so cooling is working. Ambient temps during cold months range 5degC - 20degC



Anyway, for the hotter summer months I am thinking using a heavier 15W-50. What do you think ?

The engine is a 347 stroker windsor roller cam with 0.0025" clearances (I think) and HV oil pump.

When cold at first start up it sits around 350kpa/50psi, when warmed its sits around 300kpa/44psi, and then of course hot after a run can drop to about 200kpa/30psi as stated. This is all at idle @1000rpm. Of course press goes up as rpm increase.


50psi at idle is still decent oil pressure, and the oil temp quickly recovers on cool down lap, so I don't think I have a problem or anything, its more extra protection during the hot summer months. My only concern is going to heavy, but I guess when it reaches higher op temps it wont matter.

I have read going to heavy is just as bad as going to light an oil. My understanding is:

Too High vis = poor cold start lube, increased drag, higher oil temps, loss of power.
Too Low vis = less high temp protection, durability and life. Lower oil pressure.

The type of racing I do is not sustained high rpm, its short speed events - 4 hard laps at a time, similar to qualifying laps I guess.

Thanks for any advice and guidance.

 

[ZeeOSix]

^^^ Yes, seen oil galley supply pressure is caused by the bearings not flowing all the oil volume the PD pump is supplying to the bearings. If the bearings could flow everything the pump put out, then the gallery oil pressure would essentially be at 0 PSI (1 ATM), neglecting any pressure loss from the flow in the galleries themselves and other components (assume they don't exist for this discussion).

The journal bearings are seen as flow resistance to the PD pump, even if the bearings are rotating and thereby "naturally" flowing oil. The main and rod bearings comprise the majority of the total flow resistance in an engine's oiling system. The flow resistance of other engine components on top of the bearing's resistance also contributes to the over flow resistance of the oiling system.

You fail to realize that the seen gallery oil pressure is a result of the bearing's "natural oil flow" while rotating, plus the additional side leakage oil flow through the bearing clearance due to the oil supply pressure being above 1 ATM. The graph you posted above is for non pressure fed bearing flow - it shows only half the story with a pressure fed journal bearing.

If the bearings only flowed just what the side leakage was due to their rotation, then the seen oil pressure would be even higher because the clearance for the pressurized oil to flow through would essentially look to be non-existent to the pump. It would mean that at a constant RPM and oil viscosity, the bearing would have the same side leakage no matter what the supply oil pressure was (which is what you still seem to believe, based on everything you've said in these discussions). Figure 8 above from the link you posted a while back proves that's not the case, as there is about a 50% increase in bearing oil flow volume by just raising the supply pressure by 14.5 PSI (1 bar), and keeping everything else constant.

How's that for "based on science" ... or better yet by experimental measurement? Constant RPM and constant oil viscosity (temperature) ... bearing flow goes up significantly as supply pressure increases.

What you say you believe in, and what you post never seems to agree ... why is that?

 

[Shannow]

YES, more pressure means more flow...always has always will.

NO, in spite of that, the design point is not to "jam" an oil pump's worth of volume through the bearings, it's to supply sufficient oil to meet their needs...your own papers state that "if" you can't control temperatures, add more pressure...the chart proves WHAT other than point A, more pressure flows more.

(I think I provided you with the link to the Ricardo papers)

 

[ZeeOSix]

TKFD - based on your use of the car, and the oil temps and pressures, I'd bump the viscosity up and try something like the Motorcraft® SAE 5W-50 Full Synthetic Motor Oil (used in the Ford GT and Ford Mustang Shelby GT-500, and also specified for the 5.0L Coyote engine if ran on the track). The 5W will help insure good cold start flow and protection, and the 50 on the hot end will give better thermal protection when the going gets rough.

Scroll down to the bottom of the page.
https://www.fordparts.com/Products/Chemicals-MotorOils.aspx

 

[ZeeOSix]

Originally Posted By: Shannow
YES, more pressure means more flow...always has always will.

NO, in spite of that, the design point is not to "jam" an oil pump's worth of volume through the bearings, it's to supply sufficient oil to meet their needs...your own papers state that "if" you can't control temperatures, add more pressure...the chart proves WHAT other than point A, more pressure flows more.

(I think I provided you with the link to the Ricardo papers)


Get away from the "design point" ... I could care less at this point, it's a whole different discussion so don't sidetrack. I'm just telling you that the claim that "you have always believed pressure fed bearings flow more than non-pressurized bearings" is not reflective of what you say over and over in these discussions. I gave 5 of your quotes (in blue a few posts above) from past discussions that pretty much indicate you didn't believe it then, and not sure you even really believe it now.

 

[TKFD]

Thanks ZeeOSix - you and Shanno need to buy each other a beer, lol.

Thanks for your suggestion on the Motorcraft oil, but don't like the grade spread (apparently oil has too much additives if spread too large), and I like the Penrite stuff as it has high ZDDP (2200ppm). Also, in Australia, we would never benefit from "W" anything below 10

However, I value your opinion about the upping the viscosity, and I have been tossing up whether to do it based on all the advantages and disadvantages. In the winter months would revert back to 10W-40.

Forgot to mention at full race speed (4500 - 6000rpm)on 10W-40, I think the pressure is around 450kps/65psi, which is pretty good, which makes we wonder if going 15W-50 is just a waste (of power). The concern is more when I get in from a hard run, the pressure drops significantly at idle (sometimes under 20psi) as the oil is hot. It does regain pretty quickly though.

 

[Shannow]

Originally Posted By: ZeeOSix
Get away from the "design point" ... I could care less at this point, it's a whole different discussion so don't sidetrack. I'm just telling you that the claim that "you have always believed pressure fed bearings flow more than non-pressurized bearings" is not reflective of what you say over and over in these discussions. I gave 5 of your quotes (in blue a few posts above) from past discussions that pretty much indicate you didn't believe it then, and not sure you even really believe it now.


Didn't mention it as it's SELF EVIDENT...never once have I said that the bearing block all flow that's not due to rotation...that's YOUR work.

You even claimed that I was claiming that they would suck oil from the sump up the oil pick-up which again I've not said.

 

[Shannow]

Originally Posted By: TKFD
Thanks ZeeOSix - you and Shanno need to buy each other a beer, lol.

Thanks for your suggestion on the Motorcraft oil, but don't like the grade spread (apparently oil has too much additives if spread too large), and I like the Penrite stuff as it has high ZDDP (2200ppm). Also, in Australia, we would never benefit from "W" anything below 10

However, I value your opinion about the upping the viscosity, and I have been tossing up whether to do it based on all the advantages and disadvantages. In the winter months would revert back to 10W-40.

Forgot to mention at full race speed (4500 - 6000rpm)on 10W-40, I think the pressure is around 450kps/65psi, which is pretty good, which makes we wonder if going 15W-50 is just a waste (of power). The concern is more when I get in from a hard run, the pressure drops significantly at idle (sometimes under 20psi) as the oil is hot. It does regain pretty quickly though.


You are running Penrite 10W40 racing, which has an HTHS of 4.49 according to my phone conversations with Penrite.

https://bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=3030303

HTHS is the actual viscosity that counts when it comes to bearing protection, as it's high shear (which it is on the loaded face), and 150C, which isn't uncommon in oil films.

In comparison, M1 5W50 has around the same HTHS (aka protection), as you say with a lot more polymeric VIIs, and their "Race" 0W50 only has an HTHS of 3.8.

So in terms of bearing protection, moving to these 5W50s isn't going to offer you anything whatsoever, and as you know, the Penrite Race oils are heavily additives (it's not 2,200ppm of zinc, that's too much, it's the other AW additives in it combined to 2,200ppm).

Penrite, in discussions have stated that their race oils are made to be mixed if you want to tailor make a viscosity, so you COULD start adding some 15W50 to it if you desired.

But I don't think you need to go there...their 4.49 HTHS is around 12 to 20% higher than most 10W40s and 5W40s respectively and on par with most 5W50s.

(For reference, Edge 25W50 is 6.1)

 

[ZeeOSix]

Originally Posted By: Shannow
Originally Posted By: ZeeOSix
Get away from the "design point" ... I could care less at this point, it's a whole different discussion so don't sidetrack. I'm just telling you that the claim that "you have always believed pressure fed bearings flow more than non-pressurized bearings" is not reflective of what you say over and over in these discussions. I gave 5 of your quotes (in blue a few posts above) from past discussions that pretty much indicate you didn't believe it then, and not sure you even really believe it now.


Didn't mention it as it's SELF EVIDENT...never once have I said that the bearing block all flow that's not due to rotation...that's YOUR work.

You even claimed that I was claiming that they would suck oil from the sump up the oil pick-up which again I've not said.


What are you talking about? ... you're just going in circles now.

And again ... my comment about the bearings sucking oil out of the sump was SARCASM to get a point across. I never said you claimed that, but used it as a sarcastic example because of your continuous claim that the bearings only "suck" off the galleries as needed to make up side leakage.

But again ... what I've shown is that they flow MORE than just their "natural" side leakage from rotation when they are pressure fed. I think you're so confused at this point you just spin in circles in these discussions.

 

[TKFD]

Thanks Shannow. Good advice.

So it seems that continuing to use Penrites 10tenths 10W-40 even for summer months is the best choice. I do change it half way through a season, and I change oil filter every race, and therefore cycle through new oil (600ml?) each of these times, so engine is always provided with fresh oil.

I am now actually thinking about getting a bigger oil cooler. Current one is a 19row, I'm think of a 30row, and could even use a fan, but they can be a PITA. That way I could run a 5w30 in winter months.

thoughts?

 

[ZeeOSix]

Originally Posted By: TKFD
Thanks ZeeOSix - you and Shanno need to buy each other a beer, lol.


I'd actually buy him a beer if I ever had the chance, regardless of how we both seem to come across in these threads.

Originally Posted By: TKFD
Thanks for your suggestion on the Motorcraft oil, but don't like the grade spread (apparently oil has too much additives if spread too large), and I like the Penrite stuff as it has high ZDDP (2200ppm). Also, in Australia, we would never benefit from "W" anything below 10

However, I value your opinion about the upping the viscosity, and I have been tossing up whether to do it based on all the advantages and disadvantages. In the winter months would revert back to 10W-40.


Yes, the additive package is something else to consider. I was just showing that Ford specifies this viscosity of oil for their high performance cars because they know people take them to the track and push them to their limits. Specifically the use of a higher viscosity (50) while at full operating temps.

For instance, the BOSS 302 Mustang and also the Mustang GT 5.0L (436+ HP) can run 5W-20 for normal street driving, but Ford specifies the 5W-50 synthetic for track use. Tells you something about how they believe the thinner oil isn't going to do the job in a track environment.

Originally Posted By: TKFD
Forgot to mention at full race speed (4500 - 6000rpm)on 10W-40, I think the pressure is around 450kps/65psi, which is pretty good, which makes we wonder if going 15W-50 is just a waste (of power). The concern is more when I get in from a hard run, the pressure drops significantly at idle (sometimes under 20psi) as the oil is hot. It does regain pretty quickly though.


What's the oil temperature when you see 65 PSI at 5000~6000 RPM? If the oil temperature is close to the max you ever see, then the 10W-40 might be about the right viscosity for what you're going. If the oil temps are getting much hotter than when you see 65 PSI at 5~6K, then bumping up to a xW-50 would give you some added assurance of safe bearing oil film thickness when really pushing it.

You said it has a HV oil pump, but based on the oil pressure and temperature of 100C (212 F) with 10W-40, the pressures you've seen are really close to my Z06 with thinner 5w30 Mobil 1 full synthetic. I think the stock oil pump in the LS6 might put out ~12 GPM at redline, not totally sure ... so maybe your HV oil pump is performing similar, but seems your pressure should be higher unless the oil was really hot, like around 250 deg F or above.

What's the maximum oil temperature you've ever seen after a long track run? Maybe your oil cooler isn't as effective as it could be.

 

[TKFD]

I'd like to be there when you guys share a beer, would be a debate non-the-less, lol.

Yes agree the race/track use is not the norm, and hence why I am questioning (myself) the oil choice, and it does make sense that race/track use = higher viscosity, but as you know its not quite as simple as that, as I am learning.

I don't think Ford Racing go to the depth that us racers go to WRT oil choice, so that 50wt for track use I reckon is their "safe bet" claim (well that's what I would do), and nobody would go wrong using 50wt.

Temps are not that high considering - a bit over 100degC during winter. Basically the same in summer (maybe a little bit more) but reaches it quicker and takes longer to cool down, which isn't a surprise.

Maybe my answer is getting a larger oil cooler? The added bonus is a little bit more oil volume, even though its a 7 litre pan anyway.

 

[TKFD]

I am thinking of going from 19 row to a 34 row, and decided to not go with fan, as they can restrict flow at speed. Also I have got twin radiator thermos fans that come on most times which would act as such anyway.

 

[userfriendly]

Who would want to talk shop when there is beer to be drank? After the first 6 or 7, you look for things in common.
Not until after 12 or 13, you start to argue the finer points and minor details.

 

[TKFD]

 

[Ducked]

Originally Posted By: ZeeOSix
Originally Posted By: d00df00d
Don't bother, Shannow. You've made your position abundantly clear. Anyone who has the wherewithal to follow this conversation should be able to discern your meaning.

So do you think journal bearings flow more oil as the supply pressure goes up? Or do you believe they will only flow what leaks out the sides regardless of the supply pressure?


These are not mutually exclusive, as you imply. They are both intuitively true.

EDIT : Oops. Got to the end of the thread and it seems to have spun down a bit, so please ignore the above superfluous comment, if you weren't going to anyway.ENDEDIT