octane levels

I can't think of a more shortsighted way to build an engine than to build it, and then find by trial and error after the fact which fuel is the least destructive. A true race engine had best be built with the exact fuel type in mind to take advantage of all the traits of that fuel. A street engine for the environment in which it will be living. You want the fuel that puts the most pressure on the piston for the right number of crank degrees(burn time) at the right time in crank degrees and is stable in vapor form during the cylinder fill and squeezing. Period. It's not just heat. It's stability during compresson. If the fuel can stay in vapor form until the spark lights it, you're golden. Whether that's 7.5:1, 10:1, or 15.5:1. Adding ethanol does add octane, however, the amount of ethanol must be much higher than 10% to reach a point of additional power produced. Alcohol has a bit less energy for a given volume than gasoline. So you need a lot more of it to do the same work. But, the octane rating on it is much higher, and the heat absorption of it is amazing. So you can run much higher compression ratios with it, and reap the benefits of more pressure at the right time. 10% ethanol actually replaces the gasoline molecules with less potent ones, so you are losing efficiency in an engine deisgned for gasoline. Your milage is worse on it because you are leaning out the A/F ratio and either the pc in your regular car, or your dyno guy has to compensate for it. But it does burn cleaner by the sniffer. By building an engine to make use of modern design and technology, you are not just band-aiding a built in problem of pre-ignition or detonation. You're designing those issues out so you can run common available fuel. BTW, the Ethanol levels are gogint o go up between now an 2012, IIRC up to 15%. So the builders that ignore fuel type/octane will have more issues coming as the levels rise. The best way to determine what fuel you will need is cylinder pressures. And static ratios mean next to nothing. One can build an 11.8:1 505 that runs 93 pump fuel and makes about 590hp; or one can build a 422 LA with 9.5:1 that runs on 87 pump fuel and makes around 430hp; or one can build a 12.5:1 440 that must run VP C12 that makes 480hp. The first two have dynamic compression ratios of 8.5:1 and 8.2:1 respectively. The last one has a dynamic of 10.1:1 and needs the race fuel to stay healthy. It's the interaction of piston, chamber, stroke, rod length, and cam intake lobe that gets added to the formula of static compression to figure dynamic. Play with the calc on kb-silvolite.com for some interesting relationships between parts choices. I'd rather fill a car with 87 at $4.25/gallon than C12 at $8.75/gallon. Not to mention being easier to find it at 10pm on a cruise night.