back in the early 90's i bought into a curcuit car. on our first major closed street curcuit race during qualifying we noticed our car was slower than similarly spec'd cars. it was the car not my driving! a lil investigation found the gas we were using was av gas(supplied by crew member). one of the big name racers had a lab of sorts in his trailer, so we took him a sample of our fuel. a qwik test confirmed our problem. "it's av gas" he said, "get rid of it". he showed us in a glass capillary 3 different components of our fuel make up. burnable octane @ the top was the good stuff, below that was the additives for carb icing for flying high alt's(this doesn't burn btw) at the bottom was water(fuel is hydroscopic{absorbs water}) fuel from airfields thats kept in underground tanks absorbs moisture & the octane boils off in the heat of the day. ever since i only buy proper racegas in a sealed drum. can't make gobs of power if 15% of your fuel mix don't burn!