GSX1300...A couple of years back Motorcycle Consumer News ran a story about bike oils. Engineer in Ca. tested them in a V65 Sabre for viscosity breakdown. Tests were done @ 800 and 1500 miles. Oils tested were Mobil 1, Castrol Syntech, Castrol GTX, Spectro reg, and Honda Proline. This is to the best of my memory. The results were suprising in that the 'bike' oils performed the worst. Mobil 1 retained 92+ % viscosity if I remember correctly. Syntech little less (90), followed by GTX(~87), then Honda and Spectro(~70). Again don't quote me on the numbers. I have worked at bike shops for years and still run a business building performance bike engines. I can remember the Spectro rep coming in telling us how much better their oil was. Maybe back in the early 80's, but as car motors became more like bikes the oils changed to handle the RPM's. Of course there is the clutch/tranny argument also. BOTTOM LINE.... the only 'dino' oil I use to break in customers or MY bike engines is Castrol, Valvoline especially has broken down too quick in my opinion. As far as the synthetics go they are ALL good, it's personal preference, except in the case of Megacycle Cams, they believe Mobil 1 eats cams. I DON'T. Sorry for the long post but we could debate this forever!!!! And yes we have gained 2-3hp going from 'dino oil' to Mobil 1 on the dyno in back to back runs. Usually on the smaller motors with a higher redline( less reciprocating friction)...
Dave