No. Even in a 'Vette.. As long as you use only top-tier gas, the list of retailers recommended by almost every manufacturer -- no additives are needed. - http://www.toptiergas.com/retailers/
What are you trying to achieve? Octane is the measure of the "energy" a given amount of fuel can absorb before it will combust. (Compression) The higher this number the more performance, which usually manifests itself as more miles per gallon. You might get a slightly more responsive motor, and a few more horsepower, but you're not going to win any street races based on a couple of octane rating points.
Did you raise the compression?
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