I like the synthetic oils, Mobil 1 is my personal choice. Even with synthetic, I loosen up the rod bearings on my Windosor's, get them to tight and they heat the rod big end. Last FE I did I went stock spec on all the bearings, broke it in on conventional oil and went to Mobil 1 after 2,500 miles. It's still going strong with great oil pressure some 10 years and 40,000 miles later....