This is an excellent video of how the Palisade's Atkinson cycle engine works. Gas Direct Injection (GDI) engines (like Palisade) have a reputation of fouling the intake valves with carbon deposits because gas does not flow through the valve and cannot clean it. To me, Atkinson Cycle engines have less of this worry given the fact that some gas mixture DOES flow through the intake valve. I'm hoping the cleaning properties of "Top Tier" gas can do it's job of preventing carbon build up of the intake valves. YES....I think using "Top Tier" gas is important for Palisade owners (google Top Tier Gas).