This is something that's been tugging at my brain for awhile now. We all know the chart that shows what grade of oil is recommended based on the expected environment temperatures, but I've wondered if there are conditions that would change that chart.

My reasoning is this: oil basically serves four different purposes in the rotary engine

- lubricating the apex seals and providing compression via injection
- lubricating the eccentric shaft and thrust bearing
- cooling the rotors internally
- cushioning the synchronizing gears

I also know that each of these would prefer a different viscosity for best results. For instance, the higher the viscosity of the oil, the more protected the synchronizing gears will be; the lower the viscosity of the oil, the higher the thermal conductivity and cooler the rotors will run. That's a generalized assumption however, as I can't find any comparison data for the thermal conductivity of different grades (though I do know GroupIV POA synthetic oils transfer heat about 10% faster than GroupIII and lower mineral oils). All in all, the chart that shows the grade of conventional oil to use across different temperature ranges tries to balance out the needs of those four actions.

Here are my thoughts. Would that chart change if you removed something from that list, and didn't use conventional oil? In my case, my OMP is removed. Not deactivated, but gone from the system and all the ports are sealed. The only oil the apex seals see is Quicksilver 2cycle. GroupIV/V POA/POE oils have a much higher film strength than conventional oils as well, meaning more protection for the synchronizing gears.

So does this mean that someone without an OMP and running a high-quality (POA or POE) synthetic would want to run a lower oil viscosity when subjecting the engine to prolonged high rpms and other race-like conditions? I'm not talking 0W15 here, but rather one step down or so.

 

Some race teams reduce the VI with synthetic engine oil in order to pick up a couple of extra horsepower while maintaining adequate protection. Most endurance race teams, however, tend to use the same VI in order to get maximum protection. Downing Atlanta used 20W-50 racing oil in their endurance race car engines, even with no OMP. Some drag race teams run the engine with no oil. I think it all depends on your goals. A street car is probably better off with better protection and longer engine life vs. a couple of extra horsepower.