Ah, but in an experimental aircraft running an experimental engine you can run any
oil you wish. If you are running a "certified" engine you must comply with the manufacturers recommendations or the FAA will spank you. Most if not all US certified, piston aircraft engines are of 1930s design although they have had many evolutionary changes along the way. It's just too expensive to certify a new or "revolutionary" aircraft engine given the volume of powerplants sold. When was the last time you saw a car running a magneto (other than at an antique car show)? Check your local airport and many of the bug smashers there use them.
So, in my experiemntal cobra with my experimental power plant
synthetic oil is A-OK.
