I have ran as much as 11.8 on a 383 L-t1 fuel injected combo, that was tuned. It also had enough cam, enough gear, and a stick, with a sharp owner, that understood how to drive it. Which means, don;t lug the engine. Light cars, loose converter, steep gears, all help. More cam, that reduces cylinder pressure, all help. The biggest killer, is if you lug the engine at low rpm. Depending on the application, aluminumn heads, 10.5:1 is no porblem at all. 11.5 is about max, for a car thats a but more radical, if the owner understands a few rules, and, might add a bit of race gas, or low lead 100 octane aviation fuel at certain times. If its a "true" street car, where you never plan to race it, then, I would actualy run less compression, say 9.5:1, and tune it on 87 or 89 octane. That way you can run any fuel you may come across.
I have ran E-85 on 13.5:1, with no issues. Typicaly, the difference in octane, rating, or, the amount of ethanol, in the fuel, is less only in the winter, when its cold, and no one is driving their race/street cars anyhow. Its typicaly around 70% then. If you set your tune up a bit on the fat side, which, doesn;t hurt power nearly as bad as gas, then, when you have a batch that might be a bit lower in ethanol, you have a safety factor built in. Or, buy it in barrells. I know racers who do that. They just buy drums.
Frank
Advanced Performance
www.get-ap.com