Full synthetic flows much better than natural does at low temps and maintains viscosity much better at high temps.
It doesn't break down viscosity wise the same as natural does.
To compare the two is really talking apples and oranges with an engineering "interpreter" in between trying to translate.
The 20-50 was done at a time when essentially only natural oils were available.
There were variations in that such as full Pennsylvania grade like Penn State. To me that was the absolute best of any natural oil ever marketed to the general public.
It no longer exists as full Pennsylvania grade and now is just a blend.
The other was mineral oil which I don't know much about other than it is not compatable with the other oils.
I like Mobil1 full synthetic. It has been run in race cars for around 40 years now and has shown nothing but superior characteristics at every scientific comparison.
The "ice truckers" have different issues that even full synthetic doesn't solve but unless you are constantly running well below zero Farenheit Mobil1 will do you fine.
When you rebuild you want to maintain about 1.5 thousands clearance on your bearings. If you do, even 10-30 is fine.
It has to do with film strength of the oil.
Mobil1 likes to say that it just isn't oil, it's "liquid engineering". I can't say as I argue with that.
I think also that if your engine is having issues with wet sump oil cavitation then you should be running a dry sump system.
If that doesn't work for you, take up a different hobby altogether like hot air ballooning? There is no engine oil involved in that at all?
