The gas in Phoenix is SO bad (anti-smog additives, etc.). In my previous track car (Audi A4 1.8 turbo, chipped to the point it ran with the 300 hp vette's and porsches altho the quattro helped !!!) I ran 50/50 with 100 octane unleaded and it really made a difference.

Now, with the Xfire chipped, they opened a Valeo carwash right by my office in Scottsdale, and next thing I know they sell 100 octane unleaded at 6.50 a gallon. Run 25% a lot, and 50/50 when we went to the track a couple of weekends ago. It does make a difference in the response, and really smooths out the engine in the last half of the rev range. It even sounds different !!!

Ran the same in the RS4 to get rid of a stumble in the middle range that Audi says is normal -- at 50/50 it is gone, even running 104 Octane Boost didn't do the same as the racing gas.

i just wish the station wasn't so close, it's too tempting.....................