Cast iron liners and forged pistons do not eliminate the need for a good lubricant. You still have a multitude of other things inside an engine that need to be lubricated well.

A good syn oil does a number things much better than a petroleum oil. your engine will run cooler, smoother and longer with a syn oil. Plus when you change the oil nothing will be left behind, unlike a petroleum based oil which leaves varnish and wax and dirt that it has accummulated making gunk. A good syn oil has no paraffins (which is a component of petroleum oil) to form varnishes or waxes.

Tom

Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety. Benjamin Franklin, US author, diplomat, inventor, physicist, politician, & printer (1706 - 1790)