On a stock car, there is no benefit to running 100 Octane. If you are in one of the unlucky places that only has 91, then do a 20/80 mix and you'll have about a 93 Octane blend. Anything over that is wasting money and not helping the car at all. It may even do harm over a long period of time. There is a reason it's called RACE GAS, you don'n need it in a stock street car.