If you went from a stock tune car running 87 octane to a custom tune running E85, you may pick up 30 whp. But if you upgrade from a custom 93 tune to a custom E85 tune, you will see less than 10 whp gained. E85 on both N/A and boosted cars is more for safety because it's a higher octane fuel (E85 is around 110 equivalent IIRC). But you will also drop your MPG down about 25-30% over 93.
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