I have been shopping for uncontaminated fuel (http://pure-gas.org/index.jsp?stateprov=TN ) and find that I can get 90 octane nearby. Which would be better? 90 octane uncontaminated or 93 octane with 10% ethanol contamination?

 

who sells 90 Octane ?, that sounds like an odd level, most places are 91,92, or 93 in premium.

I run Shell V-power as they don't use ethanol in that formula, which is 91 octane, but they do use ethanol in their lower octane fuels to get them past government requirements, I think that might apply to your region as well. I personally prefer a non-ethanol fuel for this vehicle as you will get better fuel economy and your fuel pump and injectors will be happier. In a stock or lightly modified S2000 you wont see any benefit from 93 octane at best, and you might even see a drop in fuel economy and power compared to a 91 at worst.

 

I prefer more ethanol... 85% of it to be exact. I don't run this car or any of my toy cars for MPG's, they all run on E85.

 

you boost guys are such show-offs lol, j/k

 

Maybe in your your location they don't but they do here in San Antonio, Texas

 

My S2000 isn't boosted . I use E85 as high octane fuel for the track that I won't have to worry about on 100F days for 20+ minute sessions. It also helps keep the motor cooler. The power gain is so minimal that you wouldn't be able to tell the difference, however, if I ever feel like building a higher compression motor, I could make use of the fuel.

Now my STi and SHO saw significant gains with E85.

 

Depends on your region. In parts of Canada you can get V-Power sans ethanol, but in other regions V-Power has anywhere from 10%-15% ethanol. That includes the states as well.