Get 100 octane. Since 100 octane is usually unleaded it won't affect your O2 sensors or catalytic converters. You can run that 24/7 is you want to. Anything higher than 100 octane is almost guaranteed to be leaded. You can run a few gallons of leaded for a few passes down the track as long as you dilute it with a full tank of unleaded as soon as you leave the track.