Oil weight reduction- ala Porsche Motorsport

[rsportvolvo]

Volvo, BMW and other manufacturers recommend a 15W-40/50 oil for extended high rpm use, i.e. racing. Unfortunately the extra protection comes with extra windage & pumping losses due to the higher viscosity oil. Porsche teams used to use Mobil 1 15W-50 for the GT3 Cup & GT3 RSR models, but they now use Mobil 1 0W-40. I first saw Posche Motorsport using Mobil 1 0W-40 oil with the Penske run RS Spyders. Now I see most Porsche GT3 teams with containers of Mobil 1 0W-40 in their paddocks. Does anyone have some tips for adjusting bearing clearances on older engines to allow the use of the lighter oil? Reducing windage & pumping losses is an area IT folks can exploit.

[Greg Amy]

Dunno about adjusting clearances, but we always ran Mobil 1 0W-40 in the ITA NX2000, starting way back in '01 or so...and I run 5W-30 in the street car.

No adjustments made...

GA

[rsportvolvo]

Would you mind sharing your bearing clearances? Do you run on the tight or loose side of the Nissan specs?

[mossaidis]

you want to be dead by morning? :)

[924Guy]

you want to be dead by morning? :)

LOL!

Depends on how creative you wanna get, doesn't it... ;) :p

[rsportvolvo]

I'm not trying to "steal" secrets or tricks, but just saying "I run it" is pretty meaningless if the associated bearing clearances are not included. Porsche and IRL cars run 0W-40, so I had references to begin with.

Let me rephrase my question as follows:

A generic car's owner's manual states the recommended oil for general use is 10W-30 or 10W-40. Said car is converted to an IT racer car with a 9/10th's build. Said engine will run 0W-40. During the engine overhaul should the owner stick to the tight side or loose side of the stock bearing clearances? How is the bearing clearance "sweet spot" determined?

I can provide some generic clearances for discussion purposes if they must be known before an answer can be given.

[924Guy]

I'd definitely say that the sweet spot would be... well... as loose as you can get away with, right?

FWIW, I run 40wt oil in my motor. Might be able to get away with a little less - never tested it out on the dyno. Still doesn't make that much pressure, anymore. Pretty well "worn out."

Seems to me that the tolerance for looseness, pun intended, would be rather engine-specific. I've heard that Chevy straight-sixes, for example, will be happy all day long with nothing more than 30psi/2 bar oil pressure. My motor, stock, before being built for racing, with maybe 160kmi, still had tight enough clearances to put out nearly 9 bar cold idle! Yes, no problems popping filters. Of course, that'll happen with a stock clearance of 8/10,000ths and dino oil! Utterly unnecessary for a race motor. Now it won't push more than 2-3bar hot and at high RPM to redline.

So far, it seems to have tolerated it. (knock on wood)

[markw]

Viscosity is rated at ambient temperature I believe. At operating temperature, they all pour about the same like water. Higher viscosity oil increases friction. Friction causes heat. Oil temperatures will rise because of this heat. I will give you my testimonial. I used to run 20-50 mobile one in the VW. At Daytona, I would see 260F oil temperature and luckily these were short races. This was with an larger external cooler. I talked about this with Redline at the Circle Track trade show. Their simplified explanation was that the additives and the viscosity were causing the higher temperatures. They suggested trying their 40WT racing and if the pressures still looked good to then try their 30Wt. Here is the testimonial part. With 40WT and no changes, the oil temperature dropped 20 degrees. Oil pressure remained as before. Next oil change switched to 30WT. Another 20 degrees oil temperature drop and hardly noticeable drop in pressure. We have used Redline 30WT in our GT cars ever since. I would not be afraid to try a lower viscosity oil. I would also not be worried about my bearing clearances even if your are pushing it to .003". Keep an eye on your oil temp and oil pressure. Less friction equal less heat and more hp. Sounds like a no brainer. As a reference, 10 pounds of oil pressure for every 1000 rpm will keep you together.

In my opinion, bearing failures are often more related to other problems, detonation and cavitiation. No oil can compensate for that type of mechanical problem. Good luck.

[Greg Amy]

Would you mind sharing your bearing clearances? Do you run on the tight or loose side of the Nissan specs?
Sorry, no idea. I could refer you to my engine builder but I'd suspect your chances are zero of getting that info...if that high. - GA

[loopracing]

Porsche first went 0W40 synthetic on the 993. I don't believe they changed any bearing clearances from previous models. The bottom end is basically the same since, right up to the GT3 models. They've stuck with 0W40 when everyone else went to 5W30. What they have changed is PCV systems, cam actuators,lifters, dry sump suction pumps. There's alot of extra machinery to lube in those engines compared to an L4 engine plus all of it it laying over sideways. Other considerations are oil intervals, emissions and preventing leaks. The GT3 has higher crankcase vacuum also. The mainseal will leak if it's not running.
I agree that running the optimum weight oil can reduce temp and increase HP. It doesn't necessarily help using synthetic. It takes more effort to pump 50WT than 30WT, which produces heat.
When i switched to 0W40 synth.(VW 1.8) from 10w40 regular, I noticed no diff in press or temp. However the valve train sounded like it was going to come apart. I surmised that solid lifter/cam clearances and lifter/head were too loose for synthetic. Plus synthetic still gets just as dirty, just as fast from blowby and condensation. Porsche has taken great lenghts with their PCV systems using cyclone separators, check valves, computer controlled valves even changing hose dia., all to manage oil mist separation and condensaion in the oil. Not to mention the cost/qt. of synth. Much more cost effective to use regular oil if possible.

[rsportvolvo]

I think I found the answer to my question here:

http://www.mae.ncsu.edu/courses/mae442/Tranmission/Journal%20Bearing.ppt#256,1,Tutorial%207%20-%20Design%20of%20a%20Journal%20Bearing

http://www.utm.edu/departments/engin/lemaster/Machine%20Design/Lecture%2026.pdf

My engineering time is free for my cars, so I don't see any reason to not pursue optimization.

Why would someone ever change oil weights and not adjust clearances to suit?

Also, the viscosity of the oil is just that, regardless of the oil type. Look at the specs and not the marketing labels.