Oil weight reduction- ala Porsche Motorsport

[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...

[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.