Get 100 octane. Since 100 octane is usually unleaded it won't affect your O2 sensors or catalytic converters. You can run that 24/7 is you want to. Anything higher than 100 octane is almost guaranteed to be leaded. You can run a few gallons of leaded for a few passes down the track as long as you dilute it with a full tank of unleaded as soon as you leave the track.
Everything over 100 octane I've ever seen for sale has ALWAYS been leaded. I've heard of unleaded on the internet that was over 100 but I've never seen it or actually heard of where someone could tell me exactly where they found it. One of the things that increases octane is the lead in the gas. That's why anything over 100 is leaded. On a side note, you can make your own 100+ unleaded by adding toluene (117 octane) or xylene (118 octane) in up to 33% concentrations to 100 octane. If you're not relatively heavily modified (400+HP) you shouldn't need race gas. BUT, it might be a good idea if you're not a very good tuner, you don't have a datalogger, or if you're running hard for a long time (IE top speed runs or road racing with a BPU car). As far as how much extra boost you can run it varies depending on your car's health. Lastly...the only place that carries race gas at the pump on a national level is Sunoco. http://www.racegas.com/Racegas/gt100locals/default.asp
Other than that you best bet is to crack open the phone book and look for mom and pop race shops that carry it...or go to your local race track.
I'm also not 100% sure on this but like nytemyst, I think there is 104 octane unlead fuel. I think it was a Citgo that carried it but again, I may be wrong. My friend put this in his POS '88 Trans Am and both of us noticed a huge improvement. The engine sounded better and would also chirp the tires which never happened on his auto.
We have a few stations that carry 100 octain and one that carries 104 octain unleaded. I have never seen anything over that. I know 114 is leaded because most pro street cars at the track run 112 or 116 oct race fuel. Good luck.
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