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PG, two of my runs have almost identical atmospherics, one with 91 and one with 105-octane. The 105 run lost about 10 hp.
I think my hp loss is about altitude. My dyno guys are forced induction guys, specializing in Subarus and Audis and they say that they get there best FI results with high oxygen fuels, like E85. They say that they typically get smaller gains even with non-ethanol high octanes, but still gains; however, the forced induction probably offsets the oxygen losses to a degree in that case.
I'd be interested to hear what your friend experienced with high altitude tuning says, if it's conventient and you get a chance to talk to him.
Still, I'll test my little theory by next week, I hope, mixing E85 with 91, right after I get a new baseline with 91 only. An 80/20 mix of 91/E85 will be less than 100-octane, but if it makes more power than 91 alone and 100 alone, then we know that oxygen is the issue. If that works, then I might try 50/50 to see if there are further gains, without deterioration in driveability.
Dave
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