Where are the gas stations that sell 93 octane... The previous owner of my car says that it is progamed to the 91 octane map, but in the owners manual it specifically says not to run 91 in a STI. Obviousley i'd prefer to run 93 and reprogram my map.......
Two things: First, if your car is mapped specifically for 91 octane it will be just fine running that as long as it's a decent tune. Secondly, the OEM STI maps are compatible with 91 octane since that's all that is available in many parts of the country. There's a tremendous amount of adaptability in the OEM maps as well as on a good reflash of the stock ECU. You shouldn't have any problems with 91 as long as the tune was done by a competent tuner.
If you're really concerned with knock prevention methanol/water injection is likely more effective and cheaper than mixing race gas with your 91. I run 27psi daily on 91octane with methanol/water injection
I do miss Michigan though... 94 octane at every sunoco