Unless they changed the rules, you can run "street" race gas (unleaded 100 octane from VP Racing and others) and take no points. I have found that if I am willing to pay the $50 extra for the fuel, the car definitely runs better. I was looking for the article I read a couple of years ago - in Australia, they tested a GT3 with regular fuel and 100 octane and measured a significant boost in power (15-18 HP, if I recall). The trick though is that you can't just show up with an empty tank and load it with race gas and go - your engine management system needs a while to get used to the "good stuff" (yummy...) and advance the timing to take advantage of the higher octane. If I am going to run in a major competition (e.g., David & Goliath shoot-out), I will run the tank down low, add about a half tank of 100 octane a couple of days before and drive it "spiritedly", then put in enough additional 100 octane for the actual race day. Zoom Zoom...
If your car is older and doesn't automatically adjust to the octane level, then obviously you would need to manually adjust for the fuel. Loading 100 octane in an engine tuned for 91 isn't going to do much (and could even cost performance, I suppose, since the slower-burning 100 octane is getting lit off "late").
One "beware" - going directly from 91 octane to 100 (and vice versa) may cause engine warning lights to come on (ask me how I know!). I now try to "blend" it in both directions. If they do come on, they should go out in a day or so - it is just that a drastic change in octane may result in a drastic change in the measured output through the cats and sensors.
A side effect is that the car really seems to run smoother on the 100 octane VP Racing - too bad I can't afford to run it very often.
I haven't run with 100 octane since early last year, but if I could afford it, I would always run it.
. Thanks.
