I always use Chevron premium (92 octane). I also have a speaker box with 2 subs (100 lbs) that I am pulling along. Yesterday was a cool cloudy day (after a big rain storm the day before), and last weekend was sunny and warm with good sticky track. Records were broke last weekend and the same guy was out again and ran .3-.4 under last weeks time. Every run that I ran I knocked off .07. I thought that I was running slower so I changed my dial in time and ended up breaking out, running the 16.84.