Very well writen, but I would not consider 8.5 to 1 compression ratios (i.e. IO-550) to be high compression. The main reason why we use leaded gas in aviation is because of it's "cushoining" effects and cooling effects. Being a former Auto tech, the majority of engines produced today are 9.0 to 1 and higher. Motorcycle engine are 12.5to1 and higher. They all can run on 91 octane. The auto makers have figured out how to make power with unleaded fuels, and higher compressions mostly with valve timing. If you can get the valve timing events right, you can make just as much power on lower octane ratings, with higher compressions.

Also, aircolled engines tend to operate at higher tempatures than liquid cooled engines. Have you ever heard an auto "diesel" when it shuts down? This is basically due to the fact that either the timing was to high causing excessie heat in the cumbustion chamber, carbon on top of the piston and in the cyl. heads cumbustion chamber being red hot and continueing cumbustion, or the temp of the engine being to high, causing again, the cumbustion chamber to be to hot and not stoping the ignition cycle.

On to the catalic convertor issue. Don't run leaded gas in anything with a cat convertor. Like you have stated, it will ruin the convertors efficency, but the EPA is misguided. Remember what the lead does to the valves and seats? It cools them. So it does the same thing to the convertor. A cool convertor works less efficently than a hot one. But what it also does is plug it up. A pluged convertor simply won't let the exhaust flow.

Now, my opnion on a need for alternative aviation fuel. It simply is not needed. The lead 100LL fuel accounts for in the atmosphere is less than 1%. But, if they want to make it work, it can be done without completely re-enginering aviation engines. So what happened to all the auto's with the improper valves and valve seats. Some of them are still on the road. What about 100 (green fuel). It contains no lead, and we can still run it in our airplanes with no ill affects. It's a simple matter of octane.

What exactly is the affect of higher octane? In it's simplest terms, the higher the octane, the slower the burn. The higher the cyl. pressure (i.e. compression ratio), the faster the burn. So a compression ratio of 10to1 will require a higher octane, or if turbocharged (increased cyl. pressure and heat) will reauire a higher octane for a given compression ratio (8to1 non-turbo=87 octane, 8to1 turbo=93octane). The more pressure an engine makes with the cumbustion process, the more heat it makes, which we have already established will lead to detonation. If we increase the octane rating of the fuel (i.e. go to 130 octane), we should not need the lead in the fuel any longer. Take the lead out, the fuel gets less expensive. Increase the octane, it gets more expensive. Back to square one with price now.

In my opnion, there is too much thought going into our fuel, when the fix is rather simple. Increase the octane that is availible(which will cool things down), take the lead out, and the problem solved.

It's late, and I have much more to type, but it's time to stare at the backside of my eyelids.