Well I can tell ya some things I do know. AVGAS is aviation fuel, illegal to use on public roads and such because there is not a road tax on it and it is a leaded fuel. 100LL is 100 octane low lead. Now that 100 octane is the aviation rating. After research from what I could find if it were at the pump it would be around 103 octane. It is tinted blue, has a much longer shelf life compared to pump gas (lets thank E85 for making it worse), doesnt create as much vapors, has additives to prevent freezing... So anyone run it in their car? Pro's? Cons? I know people that have been using it for racing engines for years, but you also find a lot of info against it as well. But doesnt everything have someone to go against the grain and say not to do it or use it? So... what does Honda-Tech have to say?

 

Something to keep in mind when using aviation fuel for automotive use is that it's very vapor resistant. That is essential because of not only temperature changes but also dramatically lower barametric pressure as altitude increases. That can make it a little harder to tune the car for street driving on a cold morning.

It was used in older carburated race cars as a cheaper alternative to racing fuel but the problem is that it's meant for high altitudes (where planes fly) and not so much low level automotive use. Lead in the fuel will kill the catalytic convertor and oxygen sensor(s) in newer vehicles and is considered illegal because of lead content. The high-octane ratings are achieved by the addition of tetra-ethyl lead (TEL), a highly toxic substance.

The only AVGAS I would even consider running in a modern emission motor would be G100UL. It's similar to the older 100LL but unleaded. It's so new that pricing may be a factor compared to other alternatives out there as well as not being easy to purchase for the average person.

 

Yeah its tough to find GU100LL. I can stop by the local airport and see if they know where I can get a hold of it. What about mixing 100LL and 93 octane? Lead will screw up O2 sensors and catalytics but a race car doesnt have a cat so no worries there. I was wondering about a mix to dilute the lead content though. You figure if 100LL straight is no more than 2 grams of TEL per gallon. Which if I am not mistaken is much more than race gas? Anyways If you did a 50/50 mix with 93 pump gas you would get 1 gram of TEL per gallon and an octane rating around 97 octane if my calcultions are correct.

 

nothing wrong with running 100LL as long as your not running a cat and dont mind replacing your oxygen sensor more often. my car doesnt have a cat and after i tuned it i pulled the o2 sensor out completely. 100LL can in no way hurt your motor.
the only real downside here is the 76 gas station isnt getting its 9.99 a gallon for 100octance out of me anymore. local airport has the 100LL for 3.86 a gallon
you will also find people with much older race cars will run this gas because it does have some lead in it and has the higher octane rating.