[Mr. Lucky]

That's all fine, but at 19.5:1 compression ration, the engine will operate more efficiently on ethanol than 87 octane gasoline.

[from occupied ga]

but at 19.5:1 compression ration, the engine will operate more efficiently on ethanol than 87 octane gasoline.

As you pointed out you can't operate at 19.5 to one on 87 octane, so yes, but you'll still get better gas mileage at 10:1 on 87 octane than at 19.5:1 on etoh