Our Hyundai vehicles have very high compression ratios but the only fuel required is an 87 octane, although the OM adds, or higher. I have read on various Forums that a higher octane fuel would 'burn cleaner' and is better for direct injection and other high CR engines. Why is this? P.S. the Turbo 2.0T gets high octane but the OM also states that 87 is all that's needed. My area: 87, 89 and 93 octane are available. Your thoughts.