"AFTER ALL, IT IS AGAINST FEDERAL REGS TO USE SYNTHETICS IN A PISTON AIRCRAFT MOTOR DUE TO HUNDREDS OF ENGINE FAILURES USING SYNTHETICS."
This is a new one on me. Recip. aircraft engines did have problems with Mobil synthetics and the resulting engine failures and law suites when it was first introduced for aircraft use, but there's no blanket restriction by the FAA on synthetics. I've been using AeroShell 15W50 with AvBlend legally for several years without a problem. The 15 viscosity is great for lubricating on cold startup, but would be too thin at operating temps, so the 50 viscosity kicks in for maintaining pressure with the wide clearances required in an air-cooled aircraft engine.
I've been using Mobil 1 20W50 in my 427 so with good results. Such a thick
oil should only be used if
oil clearances are wide, otherwise I'd go with a 10W30 or whatever the engine builder recommends. But the 20 psi at 3,000 to 5,500 rpm at 90 to 100C was too low with 10W30, thus the move to 20W50.
Note that new production engines are tightening up clearances, which require a much "lighter"
oil, such as 0W30 or 5W30 so they will be lubricated on cold startup. Why the tight oil clearances? . . . so oil pumping loss will be lower, thus more power at the crank and less fuel out of the tank. Why loose clearances? . . . for engine cooling. More oil flowing carries more heat, which is not necessary for most street engines or many race engines with oil coolers.
