My only experience has been with Valvoline straight 40 weight racing oil. I used it because all of the other Mazda racers were using it. I never lost a bearing using Valvoline. Even when busy blowing Fiat engines to pieces on various racing oils, I never lost a bearing. I did break lots of connecting rods and even then the big end would still spin fine on the rod throw.

 

Then we got well and a sponsor helped us buy some store bought big name racing engines, and we lost both back to back. One on a warm up lap at relatively low revs. It turned out that Mazda switched sources on their race bearings, and added in no quality control, so a few million bucks later they went back to their original source. Of course we had the two part racing guarantee. I rebuilt both engines using used rotor bearings and never lost another engine. From the new engines on we used Redline racing synthetic in straight 40 weight at the insistence of the builder.

 

 We pre mixed Redline synthetic 2 cycle oil at one ounce per galon. 

 

We do not stress the oil, because I use 9,600 RPM rev chips. The bearings are over sized for the stress involved and all that is required is a supply of cool oil to carry away the wedge oil heat. The film strength is very high, but is not needed at anything below (probably) 8,500 RPM.  (about the stock redline)

 

The less obvious advantage of a synthetic is that you can over heat it and it is still oil. Not the stringy black  snot that dino oil becomes under heat stress.

 

If the OMP is still in service I would use straight  30 or 40 weight Valvoline racing oil. If you premix all of the fuel, you could use a 10W-30 racing oil in cold weather but watch for foaming and monitor the oil pressure at operating temperature. If it will not hold up after an hour or so, I would go back to a straight 30 weight racing in cold weather. It is cheap enough to change regularly where a synthetic might be painful to discard. Of course you can put the spent synthetic oil in one of those many cars you drive, to help justify the added expense. 

 

Although it might be a step down protection wise, If you premix, a synthetic street oil like Mobile one would be fine.  

 

Our record for RPM with no bearing damage was close to 14,000 RPM. Before rev limiters, boy wonder was going down the face of the hill at Road Atlanta and went for a 5th to 3rd gear downshift, and stuck it into 1st gear. With a dog ring Hewland it went right in and he didn't notice the problem until he let the clutch out. (you should not use the clutch with a dog ring trans) so when the car turned side ways and a dog in the pits passed out.

 

Then the engine quit and would not restart. The rotors had touched the irons when the crank took on an "S" shape, and the solid 5.5" clutch discs had exploded, and the clutch would not release. I took the engine apart and freed up the corner seal holes, sanded the irons and stuck it back together. No problems. If that had been a piston engine, they would still be sweeping it up. The tattle tale on the Smiths flyball tach was stuck against the back side of the zero peg.

 

I do like rotaries.

 

Lynn E. Hanover