Dyno is only an indicator . . . had my H-D FXRS on the rollers. Running 91 octane at sea level. We ran out of fuel, and refueled with same brand 89 octane. Picked up 4 hp . . . . . Since 89 is less expensive than 91, that would be cheap horsepower.Exactly, most dynos are too erratic to get an exact HP reading. There are so many variables going on and any of them can cause a significant difference.