Both are correct. To maintain same reliability factor it has to be richer. If fuel volume is left the same, it can technically make more power if the air fuel is richer than optimal air fuel. Example, if a motor is calibrated to 12:1 air fuel, then you run E10 and it goes to 12.4:1, it generally will make more if that does not lead to detonation or go leaner than an optimal air fuel. In most cases, with aftermarket Supercharged motors, this pushes you just past the safety point on 91 which makes it potentially unsafe.Whipple says in a post above that "In general, the E10 requires the engine to run richer air fuel to maintain the same EGT temp, which results in slightly lower power, although very small %."
J
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