Re: 100 Octane VS 91 Octane
Interesting thread. The initial post claims 3 mpg improvement using racing gas. I've switched between midrange (89) and premium (91) and never noticed more than 1 mpg on either the roadster or my Audi A6. It's tough to drive exactly the same for two full tanks of gas and it does not take much variance in speed, acceleration, or even how much goes into the tank (before the pump shuts off) to make it seem like higher octane gas improves performance.
Sometimes the expectation of improved performance - by using higher octane fuel - is enough to skew the results, even unintentionally.
If the car is not knocking with premium, I'm not convinced it will run with more power with racing fuel. The reason they make that stuff is for high compression race cars, which we do not have.
IMHO, I could be convinced if someone held the variables more constant. Say 10 consecutive tanks of premium and then 10 of racing, and averaged the mpg. It could still be skewed, but might be more indicative of mpg.
I will go on record that I don't race my SRT6 or accelerate WOT very rarely, so midrange has been working fine.